THE NEWS MAGAZINE OF THE ESRF - ALSO AT http://www.esrf.fr/info/science/newsletter

E U R O P E A N S Y N C H R O T R O N R A D I A T I O N F A C I L I T YOCTOBER 2000 N° 34

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A Magnetic Force Microscopy image of the magnetic domains in GdFe2 thin films (top left);the diffraction image from these domains as taken on beamline ID12B (centre); and a Fraunhofer

image illustrating the nearly perfect coherence that can be obtained with soft X-rays (bottom right).In the background is the 2-D powerspectral density of the MFM picture.

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New Director General from 1st January 2001, K. Witte, PAGE 2.Hungary Joins the ESRF, K. Witte, PAGE 3.ESRF Hosts its 10th Users' Meeting, M. Cooper, PAGE 3.Beam Instability Workshop, D. Goodhew, PAGE 4.Review of the Latest Proposals for Beam Time, R. Mason, PAGE 4.ESRF Workshop for Industry: Powder diffraction on Pharmaceuticals, J. Doucet, PAGE 5.Open Days, C. Argoud, PAGE 5.Workshop on the Structure and Dynamics of the Liquid and Glassy States, D.T. Bowron, PAGE 6.Paul-Erich Zinsli, New Chairman of the ESRF Council, K. Witte, PAGE 6.32nd and 33rd Meetings of the Council, K. Witte, PAGE 7.HERCULES Celebrates Its 10th Anniversary, J.-L. Hodeau, PAGE 8.

Hard X-ray Holography at the ESRF, M. Belakhovsky, G. Faigel, S. Marchesini, M. Tegze and O. Ulrich,PAGE 11.Magnetic Speckles with Soft X-rays, J.F. Peters, M.A. de Vries, J. Miguel, O. Toulemonde and J.B. Goedkoop,PAGE 15.First Observation of Molecular Vibrational Excitations of Water with Inelastic X-ray Scattering, C. Halcoussis,T. Abdul-Redah, H. Naumann, G. Monaco and C.A. Chatzidimitriou-Dreismann, PAGE 17.Pressure-induced Landau-Type Transition in Stishovite, D. Andrault, G. Fiquet, F. Guyot and M. Hanfland, PAGE 19.Small-angle X-ray Diffraction Study of Monoolein under Pressure: Stability and Energetics of Pn3m and Ia3dBicontinuous Cubic Phases, P. Mariani, M. Pisani, C. Ferrero, A. Cunsolo and T. Narayanan, PAGE 21.Generation of Short Pulses of Hydroxyl Radicals by Synchrotron Radiation for Time-resolved HydroxylRadical Footprinting, M. Roessle, E. Zaychikov, L. Denissova, M. Wulff, F. Schotte, M. Hanfland, B. Sclavi,C. Badaut, M. Buckle and H. Heumann, PAGE 24.X-ray Imaging with Sub-100 nm Spatial Resolution at 4 keV, B. Kaulich, R. Barrett, M. Salomé, S. Oestreich andJ. Susini, PAGE 27.

In-Vacuum Undulators, P. Elleaume, J. Chavanne and P. VanVaerenbergh, PAGE 29.

A Virtual Tour into the Heart of a Synchrotron, PAGE 32.

Photography by:

C. Argoud, S. Claisseand C. Jarnias.

The ESRF Council has appointedProfessor William G. Stirling as DirectorGeneral of the ESRF to succeed YvesPetroff from 1st January 2001, for aperiod of five years.

Professor Stirling is Professor ofExperimental Physics (Condensed MatterPhysics) at the University of Liverpool.His current research interests include X-ray investigations of the magneticstructures and phase transitions ofmagnetic materials (bulk, thin films andmultilayers), which are among the coreactivities of the ESRF. Professor Stirling

has worked on these synchrotronexperiments at ESRF, NSLS, HASYLABand Daresbury. In collaboration withProfessor M.J. Cooper of the Universityof Warwick, Professor Stirling directs theUK CRG beamline, XMAS.

Bill Stirling is well acquaintedwith the Grenoble research environmentsince he worked at the ILL from 1973to 1987 and was a member andchairman of the ILL Scientific Councilfrom 1992 until 1997 and subsequentlyhas served on the ILL SteeringCommittee.

NEW DIRECTOR GENERAL FROM 1ST

JANUARY 2001

NEWSLETTER

IN BRIEF

EXPERIMENTS

REPORTS

MACHINE

DEVELOPMENT

EVENTS

Professor Stirling (left) explaining theresearch carried out on BM28 -the British XMAS CRG beamline -to Sir M. Jay, British Ambassador toFrance during his visit to the ESRF inNovember 1998.

On Thursday 10 February 2000,an arrangement was signed inGrenoble between the Department ofScientific Affairs of the HungarianMinistry of Education and the ESRFconcerning the scientific use ofsynchrotron radiation at the ESRF byHungarian scientists. The signaturetook place at the occasion of the10th ESRF Users' Meeting. Thearrangement was signed by ProfessorGábor Náray-Szabó (Head of theDepartment of Scientific Affairs ofthe Hungarian Ministry of Education)and by Professor Yves Petroff

(Director General of the ESRF).Also present during the signingceremony was Professor Denes LajosNagy, Chairman of the HungarianSynchrotron Radiation Committee.The arrangement came into effect on1 July 2000 and has been concludedfor a duration of two years. It isexpected that during this period it willbe replaced by an arrangement on thelong-term use of synchrotron radiationwith a consortium CENTRALSYNC,assembling scientific organisationsfrom the Czech Republic, Hungaryand Poland. Professor Gábor Náray-Szabó (left)

and Professor Yves Petroff (right)

HUNGARY JOINS THE ESRF10 February 2000

NEWSLETTER IN BRIEF

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??????????ESRF HOSTS ITS 10TH USERS' MEETING10 February 2000

The ESRF hosted a very successfulseries of meetings around the 10thUsers’ Meeting last February. On 8 and9 February, a workshop on FastStructural Changes was coordinated byHeinz Graafsma. The aim of theworkshop was to investigate thepossible scientific progress that couldbe made if current detection limitationswere overcome. The Plenary day(Thursday 10 February) was followedby two workshops, one on SelfOrganisation at Surfaces andInterfaces, coordinated by DetlefSmilgies, and the other on ChallengingProblems in Structural Biologycoordinated by Soichi Wakatsukiand Gordon Leonard. Each ofthem attracted approximately 100

participants, and this helped to ensurethat the total number of participantsover the five days exceeded 400. Sincethis was the tenth Users’ meeting -although “Users” meetings actuallystarted before any beam appeared - theUsers’ Organisation decided to offer aprize of 10 000 FF, twice the usualamount, to the winner of the YoungScientist Award. Richard Neutze, whocurrently works at the University ofUppsala, won the prize this year. Hepresented results covering picosecondbiology, picosecond chemistry, andsimulations of the potential forfemtosecond X-ray imaging. ThePlenary session talks also included fourother highlights from ESRF-basedresearch. Eric Dooryhee described

the fascinating detective work doneon tiny amounts of cosmetic eye-shadow taken from ancient Egyptianartefacts; Anders Liljas surveyed thecrystallographic studies of ribosomesand ribosomal subunits; RainerLuebbers discussed inelastic nuclearscattering studies of α and ε iron atpressures up to 42 GPa, and CarloMeneghini described XAFS work ondoped perovskites displaying colossalmagnetoresistance. Over seventyposters were presented in a livelyafternoon session. This was followedby a preview of the CD-ROM onsynchrotrons and synchrotron radiationby Dominique Cornuejols. Recentresults from the Medical Beamlinewere featured in a short talk by BillThomlinson, who shared a briefsession in which industrial users fromUnilever, L’Oréal and Aventisdiscussed the value of synchrotronradiation studies to their Research andDevelopment. Our thanks to all thosewho helped make these days such asuccess.

The next Users’ Meeting will beheld on Monday 19 February 2001.

M. Cooper

Dr Richard Neutze,who received the 10th

Users' meeting YoungScientist Award.

K. Witte

BEAM INSTABILITY WORKSHOP13/15 March 2000

60 participants from 19 laboratoriesfrom around the world attended theworkshop from Monday through toWednesday, 13 to 15 March. Thesubject of beam instabilities concernsmost machines and there have beenhuge developments in understanding thecontrolling techniques for theseinstabilities over the past ten years. Theworkshop was therefore an excellentopportunity to get up-to-date on thesecritical issues and to raise a number ofquestions of interest to the ESRF, forexample, understanding instabilitymechanisms, use of feedback,minimisation of impedance… Theworkshop was organised into plenarysessions in the morning and workinggroup discussions in the afternoon. Thetwo working groups dealt with “highintensity per bunch” and “multibunch”.The workshop was a frank success andseveral proposals were forthcoming:the establishment of mailing lists,

crossed participation from severalfacilities for measurements of commoninterest, benchmarking the impedanceof a few typical components withmodelling software, installation of

a test impedance in a machine,standardisation of key hardwareelements etc.

D. Goodhew

Proceedings of the workshop are available on-line:http://www.esrf.fr/machine/myweb/machine/Workshop/BIW/BIWhome.htm.

NEWSLETTER IN BRIEF

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785 new applications for beamtime arrived at the User Office for theMarch 1st deadline. Proposals camefrom labs in Europe, the USA andJapan, and from as far afield as Brazil,Korea and South Africa. A total of12 529 shifts of beam time wererequested for the current schedulingperiod, from August 2000 to midFebruary 2001.

The distribution of proposalsacross major scientific areas for thisreview round is shown in the figure

below. The nine Review Committeeswhich met on 27 and 28 April 2000selected 364 proposals (46.4%) whichwere allocated beam time totalling5 904 shifts.

R. Mason

REVIEW OF THE LATEST PROPOSALSFOR BEAM TIME

Surfaces and Interfaces 8 %Chemistry 14 %

Hard Condensed Matter:Elect. & Magn. Properties 16 %

Hard Condensed Matter:Structures 19 %

Materials Eng. & Environmental Matters 11 %Life Sciences 16 %

Methods and Instrumentation 7 %Soft Condensed Matter 9 %

The ESRF was pleased to welcomea dozen participants for the workshopdedicated to the characterisation ofpharmaceuticals by powder diffraction.The aim of this meeting was to give theparticipants an opportunity to discoverthe facilities of the ESRF and itspotential in this important and highlyspecialised domain. Participants camefrom major European companies,such as Servier, Novartis, GlaxoWellcome, Boehringer, Pierre Fabreand Laboratoire Fournier, as well asfrom smaller companies or universitylaboratories working in this field.

The programme began withscientific presentations: P.F. Lindley,Research Director, presented an outlineof the ESRF, in which he explained theproduction of synchrotron light and theinterest of the third generation sources.He also showed the reliability ofthe beam, an important parameter

for industrialists, and described thedifferent beamlines and their status.Then, A. Kvick, Head of the DiffractionGroup, and A. Fitch, scientist in chargeof BM16, gave two presentationsdedicated to the description of ID11 andBM16 beamlines and their use in thestudy of pharmaceutical powders. Theyexplained that the brightness and highresolution of the ESRF beams allowmore information to be extracted frompowder diffraction than when using aclassic X-ray laboratory source. TheESRF powder diffraction setups permitthe measurement of the utmost high-resolution data for solving crystalstructures, for quantitative phaseanalysis or real-time studies. Suchprecision is of prime importance in thestudy of polymorphism, stability duringstorage and structural changes thatare induced either by temperature,hydration and other physico-chemicalparameters, or after industrial processes

like milling, drying, grinding andtableting. Important also is the ability tomake a highly accurate comparison ofthe crystalline forms of a generic drugwith that of its original form. Finally,of great interest to the participants wasthe possibility of determining thecrystalline structure from small crystalswith dimensions as small as 10 µminstead of powders, which considerablyincreases the chance of success.

After a guided tour of the facilities,the Industrial Co-ordinator gave a brieffinal presentation. He described thevarious access modes to the ESRF thatare offered to the industrialists andgave an outline of a future service forpowder diffraction on pharmaceuticals.

Following this workshop, the ESRFhas received requests for analysis fromhalf a dozen companies.

J. Doucet

ESRF WORKSHOP FOR INDUSTRY:POWDER DIFFRACTION ON PHARMACEUTICALS

29 March 2000

NEWSLETTER IN BRIEF

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The ESRF, ILL and EMBL openedtheir doors to the public on the 20 and21 May. Almost 1400 visitors came to

discover the three research facilities.They were not disappointed as the staffwho participated in these open days did

their best to make it a very enjoyableand interesting occasion for all. In factsome of visitors who came on Saturdaywere so enthusiastic that they askedwhether it was possible to come backon Sunday as well. The programmeproposed at the ESRF permittedvisitors to discover the variousanimated areas at their own pace, and,for some, half a day did not seem to beenough for a complete visit. Afterdiscovering the storage ring from theroof of the tunnel, our visitors wereinvited to learn about the secret of theresistance of spider silk on ID13, toadmire the protein structures studied onID14 and to listen to the explanationsgiven by the staff of the MedicalBeamline (ID17).

C. Argoud

OPEN DAYS

20-21 May 2000

Visitorsgathering

around thescale model of

the ESRF.

On Monday 22 and Tuesday23 May, the ESRF played host toa workshop on "The Structure andDynamics of the Liquid and GlassyStates: X-ray and complementarymethods". Approximately 80participants united by a commoninterest in the science of structurallydisordered condensed matter systems,enjoyed a workshop programme of 20oral presentations and a lively poster

session with over 30 high qualitycontributions. Throughout this event,emphasis was placed on activeaudience participation and theprogramme was thus constructed togive ample room for lively scientificdiscussion and debate. It was pleasingto note that through the additionalsponsorship provided by the LiquidMatter Network of the UK Engineeringand Physical Sciences Research

Council and the Gruppo Nazionale diStruttura della Materia of the ItalianConsiglio Natzionale delle Ricerche, aconsiderable number of youngscientists, students and postdocs wereable to attend this event. In fact, youngscientists accounted for approximately25% of the total workshop participants.

The scientific conclusions drawnfrom this workshop were wide rangingand highlighted several of thepossibilities now raised by thepowerful instrument suites of thirdgeneration synchrotron sources.However, perhaps the most importantmessage that the participants wereurged to take away with them, was thatprogress in this complex field ofresearch can only be made through aholistic experimental approach - inparticular (and by no meansexclusively) through the combinationof neutron, X-ray and computationalmethods.

D.T. Bowron

WORKSHOP ON THE STRUCTURE AND DYNAMICS OF THE LIQUID

AND GLASSY STATES22/23 May 2000

NEWSLETTER IN BRIEF

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Since January 1, 2000, the ESRFCouncil has been chaired by Dr. Paul-Erich Zinsli, from Switzerland, whowas elected by Council for a period oftwo years at its 31st meeting on June7 and 8, 1999. He succeeds Georg vonKlitzing, Chairman in 1998 and 1999.

Paul-Erich Zinsli, 56, has beenHead of the Swiss Delegation to theESRF since 1988 and Vice-Chairman ofthe ESRF Council from 1998 to 1999.

He is a physicist by training and

did research in gamma-ray detectors,time-resolved and low-temperaturespectroscopy and molecular dynamicsat UCLA and at the University of Bern.In 1980 P.-E. Zinsli joined the FederalOffice for Education and Science inBern where today he is the DeputyDirector. His responsibilities coverresearch policy and planning as well asthe financial support of nationalresearch institutions, of internationalorganisations (CERN, ESO, ESRF, ILL,...) and of international programmes(EU-Programmes, COST).

In international organisations, P.-E. Zinsli represents Switzerlande.g. in the Steering Committee ofILL, in the OECD Global ScienceForum and in EU Fusion ResearchCommittees.

The new Vice-Chairman of theESRF Council is Robert Comès,Director of the Laboratoire pourl'utilisation du rayonnement électro-magnetique (LURE).

K. Witte

Dr Paul-Erich Zinsli,New Chairman of the

ESRF Council.

PAUL-ERICH ZINSLI,NEW CHAIRMAN OF THE ESRF COUNCIL

32ND AND 33RD MEETINGS OF THE COUNCIL1/2 December 1999 and 5/6 June 2000

At its two most recent meetings,the Council decided several itemsof importance for the scientificand organisational future of thefacility.

Scientific matters and arrangementswith third partiesAs reported earlier, the ESRF hasrebuilt its Multiple WavelengthAnomalous Dispersion (MAD)beamline (BM14) at an insertiondevice location (ID29). The Councilendorsed Management's proposal fortransforming beamline BM14 into aCRG beamline with a view to keepingit in operation as a MAD beamline forprotein crystallography, and recoveringits construction costs for the beamlinerefurbishment budget. Given that twogroups were interested, one from Spainand one from the UK, the Councilendorsed a collaborative agreementbetween these two groups: for atransition period of two years, duringwhich a further bending magnetbeamline for macromolecular studieswill be installed, the Spanish and theUK CRGs each obtain 50 % of thebeamtime at BM14; afterwards thenormal distribution of 1/3 for ESRFusers and 2/3 for CRG users will be re-established at each of the two new CRGbeamlines.

The Council noted the planned transferof the powder diffraction facility fromBM16 to an insertion device whichwill permit an increase in performanceand, at the same time, provide thesecond bending magnet beamline forthe above mentioned CRG groupsmentioned above.

The Council agreed that medium-termarrangements on the use of the ESRFmay be concluded with institutes fromPoland and Hungary for a period of twoyears, along the lines of thearrangement concluded with theInstitute of Physics of the CzechAcademy of Sciences (the arrangementwith Hungary was signed on 10thFebruary 2000 and came into effect on1st July 2000). It approved the

extension for a further five years ofthe contracts with the CollaboratingResearch Groups SNBL, D2AM,GILDA and IF, concerning theoperation of the beamlines BM1,BM2, BM8 and BM32 respectively.

With a view to a better continuity in thestaffing of the beamline teams, theCouncil raised the maximum number ofpermanent scientific appointments from30 to 35. In addition, the Council agreedthat some flexibility be introducedbetween the numbers of posts for fixed-term scientific appointments (beamlinescientists, post-docs, thesis students,altogether about 120).

Legal, procedural and financialmattersThe Council noted the scientific usemade of the ESRF over the six recentallocation periods, concluded thatthere was a significant and lastingimbalance between scientific useand contributions, and decided witha qualified majority (the Nordsyncdelegation voting against) thatcorrective measures were appropriate.To prepare such corrective actions aworking group has been established(which had its first meeting on 14September 2000).

Based on its industrial policy statementof June 1999, the Council adopted newguidelines for the use of the ESRF byindustrial companies and newguidelines for licence agreements.

The new French legislation concerningthe reduction of the working time hadled to in-depth discussions betweenManagement and staff on the workorganisation. The Council endorsedby majority the agreement on theimplementation of the 35-hour weeklegislation that the Director Generalhad signed with two Unions, andconfirmed at this occasion that, inaccordance with §12.1 of the ESRFStatutes, a close link should bemaintained between the salaries of theESRF staff and those of the FrenchCommissariat à l'Energie Atomique.

The Council took note of the finalaccounting of the construction period(1988-1998) and of the finaladjustments of contributions betweenFrance, Germany, Italy and UKresulting therefrom. It approved, withthe Italian delegation abstaining, thebudget for 2000, providing for anexpenditure of 436 245 kFF (66 505.12kEuro) in payments and requiringMembers' contributions of 404 000 kFF(61 589.40 kEuro).

The Council asked Management toremove the contribution of the ScientificAssociate Portugal towards previousconstruction costs from the incomefigures in the budget and the medium-term financial estimates but appealed toDelegations to maintain their shares inthese Portuguese back payments ontheir accounts for a possible later userwith a view to an expansion of theexperimental programme. It took noteof the correspondingly revised medium-term financial estimates for the periodfrom 2001 to 2005 and agreed theprinciples for the utilisation ofadditional income (e.g. from the sale ofBM14 and BM16) embodied therein(i.e. re-investment into the beamlineprogramme).

Appointment of Directors andChairpersonsThe Council• elected Robert Comès as its Vice-Chairman for the period from 1stJanuary 2000 to 31st December 2001;• appointed William G. Stirling asDirector General for the period from 1stJanuary 2001 to 31st December 2005;• approved that the appointment ofDirector of Research from 1st October2001 (in succession to Christof Kunz) to30th September 2006 be offered toFrancesco Sette;• approved job descriptions and adoptedprocedures for seeking candidates forappointment as Machine Directorfrom January 2002, as Director ofAdministration from February 2002 andas Director of Research (succession ofPeter Lindley) from June 2002.

K. Witte

NEWSLETTER IN BRIEF

ESRF - OCTOBER 2000

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NEWSLETTER IN BRIEF

ESRF - OCTOBER 2000

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The H.E.R.C.U.L.E.S. (HigherEuropean Research Course for Users ofLarge Experimental Systems) coursehas been running now for ten years.Since the beginning of the project in1991, more than 1200 applicationswere received, from which over 700participants were selected. Theparticipants were either Ph.D studentsor post-doctoral scientists who uselarge-scale neutron or synchrotronradiation facilities in their research.The high number of applicantsdemonstrates that this trainingprogramme answers a need expressedEurope-wide. The participants actuallycame from 18 European countries(Figure 1). The opportunity toparticipate in the course has been givento non-European candidates since 1998for the Biological session and from thisyear for the Physics and Chemistrysession. This enabled the particpationof students from China, the UnitedStates, Brazil and Argentina.

The success of the six-week coursecomes from the careful balancebetween lectures from internationallyrenowned experts, practical work at thelarge-scale facilities (about 40% of theprogramme), tutorials with localscientists, a poster session and visits tothe installations. Since 1991 eachsession has welcomed an average of 70

participants, of whom over 80%followed the training full-time, whilethe remainder attended only thelectures and classwork (Figure 2). In2000, there were 65 full-timeparticipants, 44 in Physics-Chemistryand 21 in Biology, and there were also12 part-time participants.

Each year the lectures were givenby about 60 European speakers, whoare leading specialists in theirrespective fields. An additional 100research scientists and teachers tookcharge of the practical sessions andclasswork. Most of the teachers camefrom the local scientific communityand represented a wide range ofnationalities, since several of the large-scale facilities or host laboratories,such as the ESRF, ILL and EMBL, aremultinational (Figure 3). In groups of4, the participants received 50 hoursof personalised training. It was anexcellent opportunity for participants toestablish contact with the scientists atthe large-scale facilities, and hence tobecome familiar with the potentialexisting there.

On the tenth anniversary of theHERCULES course, the associatedHERCULES X Euroconference tookplace at the ATRIA World Trade Centerin Grenoble and at the ESRF/ILL site,between 6 and 9 April 2000. Specialthanks go to I. Anderson (ILL) andV. Guerard (CNRS) for their precioushelp in the organisation of this event.More than 200 HERCULES students,

both past and present, participated inthe conference. By bringing togetherthese young scientists with carefullyselected key-note lecturers and localresearchers from the large Europeanfacilities (ESRF and ILL), theconference provided a unique trainingenvironment emphasising the latestdevelopments and applications in thevarious fields, some of which are notyet covered by the course.

EUROCONFERENCEPROGRAMME

The programme of the conferencewas structured to highlight the impactof fundamental and technologicalbreakthroughs in research centred atlarge scale facilities using synchrotronradiation and neutrons. Internationallyreputed scientists gave plenary lecturespresenting the state of the art and recentdevelopments. There were five majorthemes: Macromolecular biology,Magnetism, Imaging and Coherence,New Techniques, New Instrumentationand Industrial Applications. All of theoral sessions were well balancedwith contributions from both seniorscientists and former HERCULESstudents. This was a very good way ofgathering together confirmed and newexperts. The plenary lectures werecomplemented by poster contributionscovering a wide range of researchtopics including: Materials Science,Environmental Science, Surfaces and

HERCULES

CELEBRATES ITS 10TH ANNIVERSARY

10261

26 28

49

85217

113

1991 1992 1993 1994 1995 1996 1997 1998 1999 2000

60

50

40

30

20

10

0

A Phys Chem.B BiologyPart time

Fig. 2: Distribution perdiscipline and type ofparticipation.

ILL-ESRFFranceGermanyGreat BritainOthers

Fig. 3: Origin ofthe lecturers.

GermanySpainGreat BritainItalyFranceOther EU countriesEastern countriesOthers

Fig. 1: Numberof participantsper country.

NEWSLETTER IN BRIEF

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Interfaces, Soft Condensed Matter,Disordered systems. Each poster sessionwas introduced by parallel "clipsessions" in which participants brieflypresented their contribution.

The conference started with a shortwelcoming address by C. Feuerstein,President of Grenoble ScientificUniversity, in the presence of severalpersonalities such as H. Curien, pastFrench Minister of Research, an EUrepresentative, the Mayor of Grenoble,and representatives from varioussponsoring scientific institutions. Then ashort history of HERCULES waspresented from both the inside, byJ.R. Regnard, Director of the courseand Chairman of the HERCULES XEuroConference, and the outside, byY. Petroff, Director General of theESRF.

Chaired successively by P. Day,H. Curien and D. Raoux, the scientificsession of the first day opened withthe latest developments on medicalsynchrotron research by W. Thomlinson(NSLS and ESRF) who also presentedthe first real experiments performed atthe ESRF in collaboration with theGrenoble Hospital. Then applications ofsynchrotron radiation in magnetismand imaging with coherent X-raybeams were introduced successivelyby M. Altarelli (Director of ELETTRA-Trieste) and P. Cloetens (formerHERCULES scientist and formerESRF Young Scientist Prize Winner).

F. Mezei (HMI-Berlin) also explainedwhy we need neutrons in the 21stCentury, and M. Mezouar, aHERCULES scientist, presented thelatest results obtained at the ESRFunder extreme conditions. On thisand the following day, a largeposter session made it possible forall former HERCULES participantsto present their work. This first dayended with a session dedicated tonew instrumentation and techniqueswhich was presented by two formerHERCULES participants: P. Høghøjand M. Krisch, who spoke aboutmultilayers for neutrons and inelasticX-ray scattering, respectively.

The morning of the second day wasdedicated to industrial applications. Anoverview of applied and industrialresearch at neutron and SR facilities wasgiven by J. Doucet (ESRF and LURE),followed by examples of investigationson biological molecules of industrialinterest, presented by F. Winkler(Hoffman La Roche and Paul ScherrerInstitut). J. Webster (Mat. Eng., Univ ofSalford) and J. Pannetier (Corning SA)described applications of neutronsand synchrotron radiation to residualstress measurements and to industrialproblems in chemistry. This industrialsession, chaired by Y. Petroff, endedwith a presentation by F. Comin (ESRF)

Some official attendees at the HERCULESX Euroconference: (from left to right, first

row) H. Curien, past French Minister ofResearch, C. Feuerstein, President of

Grenoble's Scientific University, Y. Petroff,Director General of the ESRF,J.R. Regnard, Chairman of the

Euroconference, (second row) R. Maynard,Ministry of Education, C. Kunz, Scientific

Director of the ESRF, J.X. Boucherle,Grenoble City Council, J. Baruchel, co-

Chairman of the Euroconference.

HERCULES XEuroconference

attendees takeadvantage of theposter sessions to

renew or createcontacts and

collaborations.

NEWSLETTER IN BRIEF

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on the first ESRF beamline dedicatedto industrial semiconductor applications,and by R. Simon (HERCULES scientist)on a customer oriented SR source:ANKA.

The imaging and coherence sessionwas introduced by two HERCULESscientists: J. Susini and T. Weitkamp,followed by G. Grübel (ESRF) and G.Schneider (Univ. Göttingen and BESSY).It covered scattering with coherent X-raybeams, X-ray microbeams, full-fieldimaging, tomography and X-raymicroscopy. New projects, such as the X-ray free electron laser, were presentedby J. Schneider (Director of the XFELProject, DESY, Hamburg).

On the Saturday, the biologysession was introduced with anoverview on structural genomics byP. Umbach (Berlin). Several structuralbiocrystallography contributions weregiven by HERCULES scientists: A.Royant, J. Perez, C. Branca, as well as apresentation on a molecular rotary motor:ATP synthase, given by A. Leslie(Cambridge). Finally an account ofmuscle and fibre diffraction wasanimated by K. Holmes (Heidelberg).The magnetism session opened with acomparison of neutron and synchrotronX-ray results by C. Vettier (co-Directorof ILL), followed by neutron resultson bulk or magnetic thin filmsand multilayers presented by H. Zabel(Univ. Bochum) and M.R. Eskildsen(HERCULES Scientist). Example ofXMCD analysis was also given by aHERCULES scientist, S. Andrieu.

The final session, focused on thelatest instrumentation developments,was presented mainly by HERCULESscientists: T. Ursby, E. Lelièvre-Berna,H. Birkedal and S. Pascarelli, who closedthe scientific contributions with a talkentitled "what I have learnt about EXAFSsince HERCULES 1st".

The conclusions of the conference,presented by J. Baruchel (ESRF), showedthat this international, multidisciplinaryassembly of recently trained youngresearchers and leading scientists fromthe community generated a cross talk ofnew ideas on fields of applications, andhelped to define the future training

requirements on a European level.Furthermore this conference provided aunique occasion for former HERCULESstudents to mix together, renew orcreate contacts and collaborations atan international level. This event alsogave the opportunity of launching aWEB based network of HERCULESstudents, to which a large number ofthe participants have registered. Thisnetwork will provide an important meansof perpetuating the European linkscreated by HERCULES.

The proceedings of thescientific presentations have beenpublished. The HERCULES XEuroConference was also theopportunity to print a leaflet: '10years of HERCULES' whichgives a condensed report on theactivity of the Course from 1991to 2000. These documents can beobtained on request from theHERCULES organisers.

As for the usual HERCULEScourses, the schedule was tight;however, there was time forparticipants to exchange scientificand non-scientific ideas, and tojoin in common musical anddancing experiments with thehelp of a dynamic jazz orchestra"Cameleon". This unscheduledtraining session took place duringthe banquet organised on the firstday at the "Château de Sassenage"where the participants weretreated to a delightful taste ofEuropean culture and culinary

expertise: it was a huge success. Finally,to give a delicate French touch to thisconference, the concluding session endedwith a wine and cheese party offering alarge palette of different wines and morethan 50 different French cheeses!

Following this highly satisfactoryconclusion of this 10 year "Herculean"task, the HERCULES courses will,of course, continue. Please see theannouncement below for further details.

J-L. Hodeau

HERCULES 2001HIGHER EUROPEAN RESEARCH COURSE FOR

USERS OF LARGE EXPERIMENTAL SYSTEMS

Grenoble, 4 March - 11 April 2001

The Wine & Cheese party.

Session A:"Neutron and synchrotron radiation for physics

and chemistry of condensed matter"

Session B:"Neutron and synchrotron radiation forbiomolecular structure and dynamics"

Information:Secrétariat HERCULES

CNRS - Maison des MagistèresBP 166 - 38042 Grenoble Cedex 9

Tel: 33 (0)4 76 88 79 86Fax: 33 (0)4 76 88 79 81

e-mail: marie-claude.moissenet@polycnrs-gre.frhttp://www.polycnrs-gre.fr/hercules.html

Deadline for application: 20 October 2000

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I

HARD X-RAY HOLOGRAPHY AT THE ESRF M. BELAKHOVSKY1, G. FAIGEL2, S. MARCHESINI1, M. TEGZE2 AND O. ULRICH1

1 SP2M / CEA-GRENOBLE (FRANCE)2 RESEARCH INSTITUTE FOR SOLID STATE PHYSICS AND OPTICS, BUDAPEST (HUNGARY)

Hard X-ray holography permits the visualisation of the 3-D arrangement of atoms at the angstrom

level. The development and future prospects of this new technique are described.

NTRODUCTION

The knowledge of atomic andmolecular structures is fundamental tophysics, chemistry and biology. From thebeginning of this century, much efforthas been put into the developmentof reliable methods for structuredetermination. Diffraction techniques arethe most common and the most highlydeveloped for structural studies.However, not all of the problems canbe solved by diffraction: well-knowndifficulties are that single crystals cannotbe grown for all substances, and that afull structure determination is difficultfrom powder data alone. Sometimes thephase problem causes diffraction to fail –even with single crystals. As for non-periodic systems, like amorphousmaterials, quasi crystals etc., detailedstructural information cannot be derivedeasily. Further difficulties arise with newartificial materials, which have structuresthat cannot always be solved bytraditional crystallographic methods.Examples are the study of the localenvironment of low-concentrationimpurities in a sample, the atomic orderin buried interfaces, and the atomicenvironment of surface adsorbates.

Therefore, it is not surprising thatscientists are trying to find newtechniques for structural investigations.Recently, atomic-resolution X-rayholography has emerged. It is based onthe same principles as traditionalholography with light: i.e. a coherentwave (called the reference wave)illuminates the object and the detectorsurface. The intensity modulationcaused by the interference between thereference wave and the wave scatteredby the object (called the object wave) isrecorded. This interference patterncontains both the phase and themagnitude information of the object

wave. Therefore, the original wavefrontcan be reconstructed, giving the 3-Dspatial arrangement of the objects.Although holography is used in manyareas of science and everyday life,atoms in solids could not be imageduntil recently. This is because theresolution is limited by the pixel size ofthe detector and the size of source, inaddition to the wavelength. While it isrelatively easy to decrease thewavelength to the Angstrom level,giving the possibility of atomicresolution, it is difficult to reduce thesource size or to increase the detector'sresolution. Abraham Szöke pointed outthat individual atoms in a solid could beused as sources of radiation [1]. Basedon his idea, experiments wereperformed, first using electrons [2] andlater using photons [3] as hologramforming waves. Moreover, Gog and co-workers showed that the atoms presentin a sample could be used as detectorsinstead of sources of radiation [4]. Inspite of these pioneering efforts, many

problems relating to the experimentand evaluation of results remained tobe solved. The most significant oneswere the long measuring time, theexperimental setup for synchrotronstudies, background correction, andthe method of reconstruction.

These problems prompted us to starta series of experiments at the ESRF.Our aim was to develop a prototypeexperimental setup for synchrotronholographic studies and at the same timeto find reliable methods for backgroundcorrection and reconstruction. In thisarticle we would like to describe themost important results from theseexperiments. For clarity, first theprinciple of the "inside source anddetector" holography is given. In ourexperiments the electronic system of theatoms is used as sources or detectorsof X-ray radiation. Figure 1a shows theformation of a hologram in the casewhere the atoms act as point sources.A central atom is excited by an external

Fig. 1: The XFH principle for (a) inside "source" and (b) "detector"holography.

Reference wave

Object wave

Fluorescence

Source or DetectorScatterer

Direct method Inverse methoda) b)

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source. In the de-excitation process, afluorescent photon is emitted in the formof a spherical wave. This wave can reachthe detector surface directly or afterscattering by the neighbouring atoms.The two waves interfere producing anintensity modulation which is measuredon a spherical surface surroundingthe sample. The intensity modulationcontains the hologram. In the other casei.e. when atoms are used as "pointdetectors" the external wave is incidentto the sample in the form of a plane wave(Figure 1b). This can reach the centralatom directly or by scattering on theneighbouring atoms. The two wavesinterfere at the detector atom (centralatom) and the resulting field excites theelectronic system. The probability ofexcitation is proportional to the strengthof the field. Changing the direction of theincident radiation changes the phaserelation between the direct and scatteredwaves resulting in oscillations of thefluorescent intensity. These oscillationscontain the holographic information [5].

EXPERIMENTALDEVELOPMENTS

It is clear from the above description,that the two types of measurementsrequire a similar experimental setup. Themain difference is that in the insidesource case the fluorescent radiation hasto be measured as a function of thedetector position in relation to thesample. While using the atoms as "point

detectors" the direction of the incidentbeam has to be varied and the externaldetector has to collect the fluorescentphotons from the full solid angle aboutthe sample. The first step in our workwas to develop the proper experimentalsetup for synchrotron measurements. Itwas constructed in a way that both inside"source and detector" holographicexperiments could be done withoutremounting the sample. One of thecritical components of the setup is thedetection system. This should satisfythree conditions: first it has todiscriminate the fluorescent photonsfrom a relatively high background,second its angular acceptance has to bevariable from the 1*1 degree2 to the fullsolid angle (or as large a solid angle aspossible), third it has to handle highcount rates without appreciable deadtime. The mechanics is another crucialpart of the experimental setup. Althoughangular positioning and reproducibilitydo not have to be extremely precise,it does have to be fast - capable of10 turns/second for one of the axes. Forthe two other axes rotation speed can beslower, about 2 degrees/second, but theyboth have to carry relatively heavyloads (3 kg). The third part ofthe experimental setup which needsattention is the data acquisition system.During the fast motion one has to readseveral counters in quick succession(every 200 microseconds).

We developed a setup which satisfiesthe above conditions, improving thesystem after every experimental run.

Here we will not describe all the stepsbut instead present the latest version ofthe setup which uses the full power ofsynchrotron undulator radiation. Theexperiments were done at beamlinesID32, ID18 and ID22.

The experimental setup is shown inFigure 2, and a description of itscharacteristics follows. The optics are theleast complicated part. A given harmonicof an undulator is used withoutmonochromatisation since a smallbandwidth is unnecessary. However, amirror and an absorber are needed inorder to single out a given harmonic – theso-called “pink” beam – which thenpasses through a thin foil, which scatterspart of the incident beam. The scatteredradiation is used for incident beammonitoring. The mechanical systemcomprises two coaxial vertical rotationstages (θ, θ') coupled in such a way thatthe lower goniometer (θ) carries theupper one (θ'). The upper goniometer inturn holds another smaller one with ahorizontal axis (φ). The sample is fixed tothis horizontal rotation stage so that itsflat surface is perpendicular to this axiswhen illuminated by the X-ray beam. Thedetector is mounted on the lowergoniometer. The third part of theexperimental setup is the detectorassembly. Since the count rate is veryhigh, it could not be handled by singlephoton counters. Therefore, we used a Sidiode in the current mode. However,this does not have energy resolution,which is necessary to suppress theunwanted radiation, so the energy

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Fig. 2: Sketch of the experimentalsetup installed at the ESRF for thestudy of hard X-ray holographicmeasurements.

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analysis was done before the detector bya doubly focusing pyrolithic graphitemonochromator (Figure 2 [6]). Thisarrangement resulted in a large loss ofdetection solid angle compared to thelaboratory measurements. Fortunately,this was more than compensated for bythe high flux of synchrotron radiation.Typical estimated count rates were in therange of 1010 counts per second. Takinginto account the statistical noise only,this would result in measuring times of afew seconds. However, the mechanicalmotion of the sample-detector system isnot fast enough to scan a hemisphere inthis short time. Therefore, the collectionof a holographic data set at a singleenergy takes a few minutes.

HOLOGRAPHIC IMAGES

In the following part we would liketo present a few examples of holographicimaging. Useful information can bederived from the holograms without anyback-transformation. Since we use theatoms as point sources or detectors in thehologram forming process, the hologramshows the local symmetry of theirenvironments. This is illustrated inFigure 3. The pictures show the recordedfluorescence intensities, projected on thesample surface of the upper hemisphere,after absorption correction. What isreally seen is the standing wave patterns(or Kossel lines) rather than theholograms themselves, since theholographic oscillations are of muchsmaller amplitude. The pictures a, b andc were taken from samples havinga three, four and five-fold symmetryaxis perpendicular to their surface,respectively from an NiO[111] singlecrystal, an epitaxial FePt L10 film and anAlPdMn quasi-crystal. One can findother off-perpendicular symmetry pointson these holograms from which the fulllocal symmetry of the site can bededuced [7].

Of course, what we are finallyinterested in is the 3-D arrangement ofatoms in real space. The next two figuresshow an example of this. The hologramsof a CoO[111] sample are shown atfour different energies (Figure 4). Thereconstructed image of the Co atoms canbe seen in Figure 5 [7]. In the evaluationprocess all four holograms were used tobuild a single high-resolution atomicstructure. We would like to point out that

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Fig. 3: Holograms and standing wave linepatterns taken from samples having theirsurface parallel to crystallographic planewith 3 (NiO), 4 (FePt) and 5 (AlPdMn)fold axis. The FePt epitaxial film wasprepared with A. Marty and B. Gilles,the quasi-crystal was supplied byF. Schmithusen and J. Chevrier.

Fig. 5: The 3-D arrangement of Co atoms reconstructed from the holograms ofFigure 4.

Fig. 4: Holograms of CoO taken at energies6925, 13861, 17444, 18915 eV respectively.

a)

b)

c)

a)

b)

c)

d)

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in this case the resolution is isotropic incontrast to all previous measurements,and its value (0.5 Å) is near to thediffraction limit.

FUTURE TRENDS

In spite of the substantial progress inthe experimental and evaluationmethods, there are many problems whichneed to be solved before the widespreadapplication of this technique. Let us startwith the easiest one to solve: thecollection time of a hologram, which at asingle energy is between 5 and 30minutes. This does not seem too long,especially when compared with theduration of the first demonstrationexperiment (two months [3]). However,it would be advantageous to decrease themeasuring time to 1 minute or below.The reason for this is that many artifactsinherent to holographic reconstructioncan be eliminated by measuring the samesample at several (in the order of 10)energies [4,5,7]. In practical terms thiswould result in measuring a full data setfor holographic reconstruction in 10minutes instead of a few hours. Thesecond problem is that we are unable toimage light atoms. In all experiments sofar, only relatively heavy atoms (from

iron up) could be imaged. However, inmany applications especially in the caseof biological samples, it would be crucialto see O, C, N etc. The third problem thathinders wider application of holographyis the form of the sample. Presentlysingle crystal samples with a large (5*5mm2) flat surface can be measured. Itwould be very useful to extend thecapabilities of holographic imaging tosmall (~10-3 mm3) arbitrarily shapedcrystallites.

Of course there are many other areaswhere holography could be improved,but we stop here after mentioning thethree most important ones. We havecontinued to work on the abovementioned problems, and have promisingresults, especially on the measuring time,on the reconstructed cluster size and theimaging of light atoms [8] and on the firstapplication to thin films.

REFERENCES

[1] A. Szöke, in Short Wavelength CoherentRadiation: Generation and Applications, AIPConference Proc., ed. D.T. Attwood andJ. Boker (New York) 147, 361 (1986).[2] G.R. Harp, D.K. Saldin, B.P. Tonner, Phys.Rev. Lett., 65, 1012 (1990).[3] M. Tegze, G. Faigel, Nature, 380, 49(1996).[4] T. Gog et al., Phys. Rev. Lett., 76, 3132(1996).[5] For a more detailed discussion of atomicresolution X-ray holography see: G. Faigel,M. Tegze, Rep. Prog. Phys., 62, 355-392(1999).[6] S. Marchesini, M. Belakhovsky, A.K.Freund, in Crystal and Multilayer Optics, SPIEproc., 3448, 224 (1998).[7] M. Tegze, G. Faigel, S. Marchesini,M. Belakhovsky, A.I. Chumakov, Phys. Rev.Lett., 82, 4847 (1999).[8] M. Tegze, G. Faigel, S. Marchesini,M. Belakhovsky, O. Ulrich, Nature, in print.

ACKNOWLEDGEMENTS

We would like to thank the beamline staff at ID32, ID18, and ID22 for theirassistance, especially A.I. Chumakov, L. Ortega and A. Simionovici. S.M.acknowledges the E.U. Marie Curie Fellowship under grant n° ERBFMBICT961366.This work was also supported by Balaton P.A.I. n° 98024 and OTKA T022041.

The ESRF Council has openedthe selection procedure for theappointment of

• a Director of Administration(from 1 February 2002) and

• one of the ESRF's two Directors of Research (from 1 June 2002).

Both appointments are for periods offive years.

For the time being, the eightdelegations to the ESRF Council areinvited to nominate candidates.People interested in contributing tothis phase, for example by suggesting

candidates, are invited to contact oneof the Heads of Delegation beforemid November 2000. (The Councilaims at having completed therecruitment for these positions oneyear before the start of theappointments.)

APPOINTMENT OF A DIRECTOR OF ADMINISTRATION

AND A DIRECTOR OF RESEARCH

Further information on the ESRF, on the posts and on the procedure (notably the e-mailaddresses of the Heads of Delegation) can be found on the ESRF web site at

http://www.esrf.fr.

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Traditionally, soft X-rays are appliedin biology, chemistry and physicsin various forms of high-energyspectroscopies and microscopy. Whilethese techniques are still important, thereis a growing attention for soft X-rayscattering. This may seem surprising,since the wavelengths in question, 5 Åand longer, are too large to fit interatomicdistances. However, they do fit thelength scales involved in the bloomingfield of ‘nanoscience’, as well as thecorrelation lengths occurring in manysolids, such as superconductors andmagnetic materials. Usually this sizerange is addressed by small-anglescattering (SAX) at hard X-ray energies(E > 5 keV). Because of the veryhigh absorption coefficients at longerwavelengths, soft X-ray scatteringis a technical challenge, requiringcomplicated vacuum beamlines, vacuumdiffractometers, and thin samples.

WHENCE THENTHE ATTENTION FOR

SOFT X-RAY SCATTERING?

The answer is found precisely inthose strong absorption effects. Bytuning the X-ray energy to an absorptionresonance of a specific element, one canobtain a large increase in the sensitivity

to that element. Furthermore, magneticor crystal field effects that break thespherical symmetry of the atom give riseto polarisation-dependent scatteringeffects. Resonant scattering experimentsare possible at the absorption edgesdown to the K levels of the lightelements C, O, and N, important inbiology and chemistry. However, at themoment the magnetism community ismost active in exploiting resonanteffects. These basically arise frommagnetic dichroism: the dependence ofthe absorption coefficient on themagnetisation in the material and thepolarisation of the light.

The first soft X-ray magneticscattering experiments have beenperformed on artificially orderedmagnetic structures in the form ofmagnetic bi- and multilayers. Last year,it was shown that it is also possible toobtain information on magnetic domainstructures in thin films. In thisexperiment [1], polarised X-rays werescattered off FePd thin films in which themagnetisation self-organises in so-calledmagnetic stripe domains (see inset).These structures act as a magneticgrating that produces well-definedsatellites around the specular reflectedbeam. By varying the angle of incidence,it was shown that one can also obtaininformation on the domain structure

below the surface, which is veryimportant since most domain imagingtechniques only probe the magneticprofile of the fringe fields just outside thesample surface.

Recently, in a variant of theseexperiments on ID12B we have used aSAX-type transmission geometry, asshown in Figure 1. A 15 µm diameterbeam was incident normally on a 35 nmthick film of amorphous GdFe2 showinga pattern of 110 nm wide meanderingmagnetic stripe domains (Figure 2a.).Off-resonance, only the transmittedbeam is observed. This changes radicallywhen the energy of the beam is tuned tothe Gd M5 resonance (λ = 1.1 nm). Herethe magnetic scattering cross-section isenhanced by orders of magnitude [2] anda clear first order and a much weakerthird order (not shown) magnetic

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MAGNETIC SPECKLES WITH SOFT X-RAYSJ.F. PETERS, M.A. DE VRIES, J. MIGUEL, O. TOULEMONDE AND J.B. GOEDKOOP

VAN DER WAALS-ZEEMAN INSTITUTE, UNIVERSITY OF AMSTERDAM (THE NETHERLANDS)

Soft X-rays are rare at the ESRF. Nevertheless, the ESRF’s soft X-ray user community has a clear

impact on synchrotron radiation research due to the capabilities of the source. In this article we

want to highlight new developments in magnetic soft X-ray scattering.

Fig. 1: Experimental layout. Note that the whole optical path from front end toscintillation screen is under ultra-high vacuum.

Fig. 2: (a) Magnetic force microscopy(MFM) image of the meanderingmagnetic stripe domains in a 35 nmthick film of GdFe2. The width of thedomains is 110 nm. (b) Parallel stripedomains obtained after saturation of asample in an in-plane magnetic fieldapplied along the stripe direction.

diffraction ring appears (Figure 3). Thetotal scattered intensity in the ring is1.5 x 106 photons/s.

A closer look at Figure 3 reveals thatthe intensity in the ring has strongspatial fluctuations. These are staticmagnetic speckles, a result of thedisordered magnetic structure in thescattering volume. Prior to thisobservation, magnetic speckles werereported on a Bragg diffracted peak ofUAs [3]. Even though Figure 3 wasrecorded with non-optimisedconditions, the speckle contrast is~30%, indicating partial coherence witha coherence length of 5 µm. That onecan do better is shown in Figure 4,which represents the Fraunhofer patternof a 10 µm-diameter laser pinhole. Itshows extremely regular diffractionrings up to the 24th order, implyingnearly complete coherence. It wasproduced from the vertically convergentbeam behind the vertical focusing

mirror by collimating the beam with300 x 500 µm slits, 1 m upstream fromthe pinhole (Figure 1). The total flux inthis pattern is estimated at 1.3 x 107

photons/s.

As mentioned previously by Yakhouet al. [3], magnetic X-ray intensityfluctuation spectroscopy may be madepossible by using such high fluxes.Probably the best chances for achievingthis lie in the soft X-ray range, due tothe inherently higher coherence lengthof soft X-ray undulators and the largermagnetic contributions to the scatteringcross section. That being said, a largenumber of problems have to besurmounted. Primary concerns are theflux and the stability of the beamline.Hopefully the move of beamline ID12Bto straight section ID8 will overcomethese problems because it will then havea full length undulator with anestimated 10 times higher flux and amore stable optics layout.

REFERENCES

[1] H.A. Dürr, E. Dudzik, S.S. Dhesi,J.B. Goedkoop, G. van der Laan,M. Belakhovsky, C. Mocuta, A. Marty,Y. Samson, Science, 284, 2166-2167 (1999).[2] J.P. Hill, D.F. McMorrow, ActaCrystallogr., A52, 236-244 (1996). [3] Yakhou et al., ESRF Newsletter, 32, 12-13(2000).[4] A. Huber and R. Schäfer in MagneticDomains and references therein, SpringerVerlag (1998); C. Kittel, Phys. Rev., 70, 965-971 (1946).

ACKNOWLEDGEMENTS

We thank the staff of ID12B andthe authors of [1] for their help andcontributions, and Otto Hopfner fortechnical assistance. This work ispart of the research program ofthe Foundation for FundamentalResearch on Matter (FOM) and wasmade possible by financial supportfrom the Netherlands Organisationfor Scientific Research (NWO).

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Fig. 4: Fraunhoferdiffraction patternfrom a 10 µmpinhole illuminatedby a coherent beamof 1183.6 eV X-raysat ID12B. The totalflux in this image is1.3 107 photons/swith a 80 mA 16bunch beam.

Fig. 3: Magnetic speckleobserved on the first ordermagnetic diffraction ringin transmission from thesample described inFig. 2a, illuminated by a15 µm diameter beam ofcircularly polarised X-rays tuned to the Gd M5resonance at 1183.6 eV.A beam stop blocked thedirect transmitted beam.The radius of the ringcorresponds to a ~115 nmdomain width.

Domains in magnetic thin films with aperpendicular magnetic anisotropy arethe result of the competition betweenthe magneto-static energy, which,to minimise the stray field, tendsto an in-plane magnetised film (Figure 5a), and the perpendicularanisotropy, favouring an out-of-planemagnetisation (Figure 5b). A configuration with alternating upand down domains (Figure 5c),reduces the stray field of the samplewhile most of the sample isperpendicularly magnetised, loweringthe perpendicular anisotropy energy atthe cost of creating domains walls [4].Many different domain patterns arepossible for the alternating up-downprofile, for example the maze-likedomain pattern and the perfect parallelstripes shown in Figure 2.

MAGNETIC DOMAINS INTHIN FILMS WITH A

PERPENDICULAR MAGNETICANISOTROPY

Fig. 5:Magnetisationprofiles in a thinfilm, (a) uniform in-planemagnetisation, (b) uniformperpendicular magnetisation, (c)alternating up and down domains.

a)

b)

c)

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The ubiquitous condensed mattersystem called "liquid water" has alwaysbeen in the focus of fundamentalresearch. In particular, the manner inwhich it renders the earth fit as a habitatfor life, and its involvement in lifeprocesses at all levels has inspiredgenerations of researchers. Nowadays, itis widely known that most of the uniquephysicochemical properties of liquidwater are intrinsically related to the hugeamount of H-bonds, which determine itsstructure and dynamics from themacroscopic to the microscopic spatialand temporal scales. Additionally, therole of water in the formation andstabilisation of biologically significantstructures is well known.

In the last few decades it has beenrecognised that quantum mechanical

effects appear to play a dominant rolein the proper microdynamical descriptionof water due to the small massof the hydrogen atom. Nowadays,modern spectroscopic techniques likeneutron and X-ray scattering areindispensable for the study of matter inthe mesoscopic and microscopic spatio-temporal domains. Extending the basicresults obtained with inelastic neutronscattering, the recent development ofthe novel inelastic X-ray scattering(IXS) technique at a third generationsynchrotron radiation source, the ESRF,has also led to a new interpretation of animportant phenomenon in liquid water,i.e. a propagating "fast sound" collectivemode at the mesoscopic scale [1].

The primary goal of our recentexperiment (February 2000) at beamline

ID16 was to take the first measurement ofthe spectra of intramolecular vibrations(or, in other terms, localised vibrationalexcitations) using the IXS method.The OH stretching vibrational modesof water are about 400 meV. Before ourexperiment was performed, the possibilityof observing such spectra had beenquestioned by many due to the very lowintensity available at the spectral regimeunder consideration. Figure 1 shows thevibrational spectra of pure H2O, pureD2O and a H2O-D2O mixture with anequimolar H:D composition, i.e. H:D =1:1. The accumulation time required foreach of the spectra shown was about 40hours. The spectra are presented asmeasured, i.e. no smoothing has beenapplied. The peaks due to the OH and ODstretching vibrational modes are clearly

FIRST OBSERVATION OF MOLECULAR VIBRATIONAL EXCITATIONS

OF WATER WITH INELASTIC X-RAY SCATTERINGC. HALCOUSSIS1, T. ABDUL-REDAH2, H. NAUMANN2, G. MONACO1 AND C.A. CHATZIDIMITRIOU-DREISMANN2

1 ESRF, EXPERIMENTS DIVISION

2 I.N. STRANSKI INSTITUTE, TECHNICAL UNIVERSITY OF BERLIN, BERLIN (GERMANY)

The inelastic X-ray scattering (IXS) technique has been applied to the energy transfer regime of

molecular vibrations of covalently bonded H atoms, ca. 0-500 meV. We have obtained, for the first

time, convincing experimental evidence that IXS can be used for vibrational spectroscopy.

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Fig. 1: The IXS spectra of the intramolecular OH andOD stretching modes of H2O, D2O, and a H2O-D2Omixture with an equimolar H:D composition (H:D = 1:1).The spectra are parallelly shifted, for illustration.Intensities are given in arbitrary units. (For the H2Ospectrum, a typical count rate at 400 meV was about 0.4 - 0.5 counts/s).

Fig. 2: The corresponding spectra of H2O, D2O, andthe equimolar H2O-D2O mixture (H:D = 1:1) obtained withthe conventional Raman light scattering technique (afterstandard data analysis). The spectra are parallelly shifted,for illustration. Intensities are given in arbitrary units.(Typical count rates at the maximum of the OH peaks wereca. 100 to 200 counts/s).

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visible, and they are centred about400 meV and 300 meV, respectively.These peaks are superimposed on the"long tail" of the much more intensivequasielastic peak. For the sake ofvisibility, the spectra are parallelly shifted.For the H2O spectrum, a typical count rateat 400 meV was about 0.4 - 0.5counts/second. The momentum transferchosen in these experiments was 2.9 Å-1.The incident energy was 13.8 keV.The spectral resolution used wasabout 12 meV. For comparison, thecorresponding Raman light scatteringspectra are shown in Figure 2. (An Argon-ion laser with excitation wavelength of5140 Å was used. Typical count rates atthe maximum of the OH peak were ca.100 to 200 counts/second.) One can easilysee that with both methods the samespectral positions of the OH andOD peaks were obtained. Obviously, thedetermination of the spectral peak shapesand widths of the IXS spectra requirebetter counting statistics.

The second goal of our IXSexperiment was to investigate thepossibility of observing quantumentanglement (QE, cf. side panel) betweenthe vibrational modes of liquid water. QEand/or Schrödinger’s cat states of quantumparticles play a dominant role in numerouspresent day investigations of fundamental(theoretical and experimental) physics.Moreover, articles about "quantum

computer", "quantum cryptography" and"quantum teleportation" can be foundeven in rather popular journals; see forinstance [2]. However, one conventionallyexpects that the observation of QE effectsis impossible in condensed matter at roomtemperature, due to the extremely fastdecoherence process [2,3] which destroysthese quantum effects.

In our neutron Compton scattering(NCS) experiment on water and H2O-D2O mixtures [3] we have provided thefirst direct experimental evidence forQE between protons in water at roomtemperature. The NCS technique ischaracterised by a short scattering time(or interaction time of neutrons withprotons) of about 1 femtosecond. Themost surprising result was that, due toprotonic QE, the cross-section densityof H becomes reduced anomalouslyby up to 30%. In simple terms, QEseems to effectuate destructive quantuminterference between protons, in the sub-femtosecond time scale [3]. Since OHoscillators contain protons, this strikingNCS result indicates that the quantumdynamics of OH vibrations (and H-bonds), and the associated IXS spectra,could also be affected by protonic QE.

In future work, after further IXS dataaccumulation, we intend to determine theintegral scattering intensities of the OHand OD peaks of the samples mentioned

above (see Figure 1). If QE betweenvibrational degrees of freedom is presentin water, then an anomalous change ofthe X-ray scattering cross-sectiondensity of the OH mode will bemeasurable. Concretely, the integralcross-section density of the OH mode ofthe H2O-D2O mixture would then besmaller (say, by ca. 10%) than that of thepure H2O. In this case, one wouldobserve the surprising effect that ca.10% of the OH oscillators of the H2O-D2O mixture would become "invisible"to the X-rays. It may be noted thatneutron scattering is due to the stronginteraction, whereas IXS is due to theelectromagnetic interaction. Thus it willbe interesting to compare the anomaliesfound with NCS [3] with the associatedIXS results. If successful, our IXSexperiment on water will reveal novelcharacteristics of short-time quantumdynamics of protons (and H-bonds) incondensed matter.

REFERENCES

[1] G. Ruocco, F. Sette, U. Bergmann,M. Krisch, C. Masciovecchio, V. Mazzacurati,G. Signorelli, R. Verbeni, Nature, 379, 521-523 (1995).[2] A. Zeilinger, Quantum teleportation,Scientific American, 282 (no.4), 32-41, (April2000). [3] C. A. Chatzidimitriou-Dreismann,T. Abdul-Redah, R. M. F. Streffer, J. Mayers,Phys. Rev. Lett. 79, 2839-2842 (1997).

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Consider two dice (say, A and B) whichare rolled. As conventionally assumed,each dice on its own should be fair andyield random results. The two outcomesof a throw with the two dice are thencompletely uncorrelated.

Of course, dice are classical objects.Nevertheless let us now make the(fictitious) assumption that the two diceare quantum objects. After rolling of thedice pair, its wavefunction, say ΨAB, canbe constructed with the aid of the"single-dice" wavefunctions ΨA(i) andΨB(j), where i and j are possibleoutcomes, that is, natural numbers from1 to 6. There are many different forms ofΨAB that are permissible according toquantum theory. Some of them – in fact,the majority of them – appear to havecompletely counter-intuitive properties. Here let us give a particular example of

such a state (which is adapted from Ref.[2]). E.g., for the specific case of "equaloutcomes", the following dice-pairwavefunction (before an actualmeasurement of the outcomes; seebelow) is permissible according to thefundamental Superposition Principle ofquantum mechanics (see any textbook):

ΨAB = const. * [ΨA(1) * ΨB(1) +ΨA(2) * ΨB(2) + ... + ΨA(6) * ΨB(6)]

(1)The physical meaning of this ΨAB maybe described as follows: The outcomesof both dice A and B are equal to 1 and,at the same time, they are equal to 2, ......, and, at the same time, they areequal to 6. This specific quantum statehas no classical analogue and thus it iscompletely counter-intuitive.

An actual measurement of the twooutcomes "reduces" ΨAB to anotherwavefunction, say ΦAB. E.g., if one

actually measures a "double 5", thenthe wavefunction of the dice pair afterthe measurement is

ΦAB = ΨA(5) * ΨB(5)(2)

[This is according to the standardtheory of measurement; in technicalterms, applying the von Neumannprojection postulate.] Clearly, incontrast to (1), the wavefunction (2)has a classical analogue.

A pair of quantum systems being ina quantum state like (1) – but not like (2)– is called entangled. Quantum states like(1) are also called Schrödinger’s catstates, Einstein-Podolsky-Rosen states,etc. Nowadays, entangled pairs ofquantum objects (e.g., photons or ions,which must be very well isolated fromtheir environment) can be produced inthe laboratory; cf. [2].

QUANTUM ENTANGLEMENT (QE) OF TWO SYSTEMS

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There is no close-packed compactionic arrangement for metal dioxides.The most common dense form of XO2compounds (where X is Si, Ti, Ge,...) isrutile, in which the oxygen sublattice canbe seen as largely distorted face centeredcubic, and where only one of the twooctahedral sites is filled by silicon(Figure 1). There are several other denseforms for the XO2 compounds, becausecomparable energies are found forslightly different octahedral inter-links.For example, six polymorphs have beenreported for PbO2, between ambientpressure and 47 GPa [1]. The sequenceof the SiO2 phase transformationsdown to the core-mantle boundary(CMB) of the Earth needed furtheranalysis because it can affect thelower mantle composition through apossible breakdown of the major lowermantle mineral, the (Mg,Fe)(Al,Si)O3perovskite, into a mixture of stishoviteand magnesiowustite.

Synthetic crystals of quartz werefinely ground, mixed with platinumblack, and loaded in a membrane-typediamond anvil cell. After each pressureincrease, the sample chamber was slowlyscanned by the infrared radiation of amultimode regulated YAG-laser. Thislaser-annealing technique is a veryefficient method of relaxing the samplestress and leads to a quasi-hydrostaticpressure in the pressure chamber,improving the quality of the X-raydiffraction spectra [2,3]. Angle-dispersive X-ray diffraction spectrawere recorded at the ID9 beamline.A water-cooled Si (111) bent Laue

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PRESSURE-INDUCED LANDAU-TYPE TRANSITION

IN STISHOVITED. ANDRAULT1, G. FIQUET2, F. GUYOT2, M. HANFLAND3

1 LABORATOIRE DES GÉOMATÉRIAUX, INSTITUT DE PHYSIQUE DU GLOBE, PARIS (FRANCE)2 LABORATOIRE DE MINÉRALOGIE-CRISTALLOGRAPHIE, UNIVERSITÉ PARIS VII AND IPGP, PARIS (FRANCE)3 ESRF, EXPERIMENTS DIVISION

Rietveld structural analysis of SiO2-stishovite could be performed up to 120 GPa by angle-dispersive

X-ray diffraction in a YAG-laser heated diamond anvil cell. At 54 GPa, a second-order pressure-

induced lattice modification occurs. Above this pressure, the CaCl2-type SiO2 compresses without

additional decrease of the shortest known O-O bond found in stishovite.

Fig. 1: Dense atomicarrangement for silica.One half of the octahedralsites of the oxygensublattice are filled by Siatoms. SiO6 octahedrashow 4 equatorial and 2polar Si-O bonds.The CaCl2-distortionoccurs when oxygenescapes from the diagonalof the (a,b) plane, thuschanging symmetry fromtetragonal toorthorhombic.

Fig. 2: Typical twodimensional diffractionpattern recorded ona mixture of SiO2-stishovite,NaCl pressuretransmitting medium,and Pt YAG-absorber.This pattern wasrecorded at 11.7 GPa,after laser heating toabout 2200 K in thediamond anvil cell.

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monochromator was used to produce abright monochromatic X-ray beam at awavelength of 0.4561 Å. Vertical andhorizontal focusing was achieved with aspherical mirror and a monochromator,respectively. The X-ray flux on a15*15 µm spot allowed acquisition on animaging plate in about 10 minutes [4].The two-dimensional images (Figure 2)were integrated using the program Fit2d.Lebail and Rietveld profile refinementswere applied to all diffraction patternsto extract cell parameters and volumesfor SiO2 and platinum, and to compareexperimental intensities with thosecalculated for different structural modelsof SiO2.

Analysis of the X-ray diffractionspectra indicates that the sample consistsof a mixture of platinum and stishoviteup to 53.2 GPa. The spectrum recordedat 54.8 GPa shows slight modificationsrelated to the onset of a transformationfrom stishovite to a CaCl2-distortion ofstishovite. At 62.4 GPa, the diffractionpeaks located at around 1.45 and 1.78 Åbecome doublets, which the stishovitemodel fails to explain. Instead, themodelled spectrum of the CaCl2-distortion of stishovite fits theexperimental profile. The occurrence ofthe CaCl2-polymorph at about this

pressure agrees with previousexperimental reports using either X-raydiffraction [5] or Raman spectroscopy[6]. It also agrees with ab-initio structuresimulations that proposed a CaCl2-distortion, but is in disagreement withother experimental or theoretical studiesthat proposed the occurrence of a post-CaCl2 polymorph at pressures below120 GPa, at the pressure conditions ofthe Earth's lower mantle.

Evolution of c/a and c/b cellparameter ratios (Figure 3) clearlyshows the stishovite to CaCl2-formtransition: there is an increase in theCaCl2-distortion with increasingpressure up to 120 GPa. The rapidmodification of the a and b cellparameters above 54 GPa is achievedby a rapid rotation of the SiO6 octahedrain the (a,b) plane, as supported by thepressure evolution of the (x,y,0) oxygencoordinates. We note a change in thepressure evolution of the shortest O-Odistance above the transition pressure.In the CaCl2-structure, the compressionoccurs without further decrease in thisshortest O-O distance. Instead, theother O-O distances diminish toward acomparable value, and consequentlythe oxygen sublattice becomes moresymmetrical.

The pressure evolution of the a and bcell parameters is similar to that usuallyfound for a Landau-type temperature-induced transition. Using a standard typeof representation for such a transitionwith the (a-b)/a ratio as an orderparameter, results indicate that the CaCl2-form is the lower entropy polymorph.Therefore, the CaCl2-form may be thelow-temperature polymorph of stishovite.This gives weight to the argument fora positive slope of the boundarybetween the two silica polymorphs in a P-T diagram. The critical temperature ofthe phase transition (Tc(P)) would reachT = 300 K, when pressure reaches54 GPa. This means that while furthercompressing silica at room temperature(Texp) above 54 GPa we increase the gapbetween the experimental and criticaltemperatures (the gap is Tc-Texp). Forsuch a second order transition, anincrease in (Tc-Texp) explains theincrease of the CaCl2-distortion thatwas observed.

We observed a continuous increasein the SiO2 density up to pressuresfound at the Earth’s CMB, because thephase transformation to the CaCl2polymorph do not involve noticeablemodification of volume or bulkmodulus. From these new data wecalculate a positive ∆V for the MgSiO3=> MgO + SiO2 breakdown reaction atall pressures. Therefore, the silicateperovskite is denser than a mixture ofits oxides down to the CMB.Consequently, the proposal that freesilica could occur in the Earth’s lowermantle is not supported by thepresent data, as long as an excessof magnesiowustite (Mg,Fe)O isbelieved to be present in the lowermantle.

REFERENCES

[1] J. Haines, J.-M. Léger, O. Schulte, J.Phys. Condens. Matter, 8, 1631 (1996).[2] G. Fiquet, D. Andrault, J.-P. Itié,Ph. Gillet, P. Richet, Phys. Earth Planet. Int.,95, 1 (1996).[3] D. Andrault, G. Fiquet, M. Kunz,F. Visocekas, D. Häusermann, Science, 278,831 (1997).[4] D. Häusermann, M. Hanfland, HighPressure Res., 14, 223 (1996).[5] Y. Tsuchida and T. Yagi, Nature, 340, 217(1989).[6] J. K. Kingma, R. E. Cohen, R. J. Hemley,H. K. Mao, Nature, 374, 243 (1995).

Fig. 3: Pressure evolution of the unit cell parameters showing a rapid increase in thedifference between a and b axes above 54 GPa. The evolution with pressure of the(a-b)/a order parameter indicates a classical Landau-type evolution, with the CaCl2-form being the lower entropy polymorph.

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L

SMALL-ANGLE X-RAY DIFFRACTION STUDY OF MONOOLEIN

UNDER PRESSURE: STABILITY AND ENERGETICS OF PN3M AND

IA3D BICONTINUOUS CUBIC PHASESP. MARIANI1, M. PISANI1, C. FERRERO2, A. CUNSOLO2 AND T. NARAYANAN2*

1 ISTITUTO DI SCIENZE FISICHE AND INFM, UNIVERSITÀ DI ANCONA (ITALY)2 ESRF, EXPERIMENTS DIVISION

* CORRESPONDING AUTHOR

A bicontinuous cubic liquid crystalline phase is one of the most fascinating structures exhibited by

water/amphiphile systems. Not only do the structure and dynamics of these cubic phases make

them attractive as model soft matter systems, but they also have many practical applications.

Small-angle X-ray scattering can reveal the symmetry as well as the topology of these structures.

ipids are natural examples ofamphiphilic molecules having a polarhead and a non-polar tail. Because ofthe hydrophobic character of the largenonpolar tail, and other factors such aspacking and steric constraints, van derWaals and electrostatic interactions,these molecules exhibit a variety ofself-assembled states when mixed withwater. Which state predominatesdepends on the concentration andthermodynamic parameters such astemperature and pressure. In neutrallipids, the polar head group bears nonet charge under biological pH.Monooleoylglycol (monoolein) is onesuch lipid, which is well known for itsmesomorphism in the hydrated state. Itis a workhorse lipid involved in fatdigestion. On the mesoscopic scale,monoolein molecules in water organiseinto a wide variety of structures ofwhich bicontinuous cubic phases arewell known. These cubic phases havefound application in the crystallisationof a variety of bacterial membraneproteins. Understanding the relationshipbetween microstructure and phasestability is important in the study oftheir biological function. The stabilityof bicontinuous cubic phases and theability of a lipid membrane to bend aregoverned by the bilayer elasticcurvature energy.

At normal pressures, the monooleinand water mixture shows a variety oflyotropic phases. These include alamellar phase (Lα) in which molecules

assemble into stacked sheets (as shownin Figure 1a), an inverted hexagonalphase HII consisting of cylindricalstructural elements packed on a 2-Dhexagonal lattice, and two invertedcubic phases with space groupsymmetries Pn3m and Ia3d [1,2]. Asdepicted in Figure 1, the cubicstructures are formed by mid-planes ofbilayers satisfying the condition forperiodic minimal surface (meancurvature → 0) [3,4]. Consequently, thissystem is suitable for testing the

proposed curvature free energy modelof lyotropic phases [3].

Hydrostatic pressure can be used toinfluence the structural properties andthen to obtain an extended descriptionof the phase behaviour, stability andenergetics of cubic phases. Small-angleX-ray diffraction is a powerful tool forelucidation of the symmetry as well asthe topology of these structures.Measurements were performed on theID2 beamline at the ESRF. Monoolein

a)

c)b)

Fig. 1: (a) Schematic view of the cross-section of a lipid bilayer showing thehydrophilic head and hydrophobic tail of the lipid molecules. Computed periodicminimal surfaces corresponding to Pn3m (b) and Ia3d (c) cubic symmetries,respectively (courtesy of S. Hyde and S. Ramsden, Australian National University).In (b) and (c) each of the triply periodic minimal surfaces is formed by the lipid bilayer.

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samples were studied at differentdegrees of hydration (water content) asa function of pressure up to 3 kbar.A typical 2-D diffraction patternfrom an Ia3d cubic phase is shown inFigure 2. Typical, azimuthally-averagedintensities as a function of scatteringvector s (= 2/λ sinθ) at differentpressures are depicted in Figure 3.

Results show that the pressure induces atransition from the Ia3d cubic to thelamellar Lα phase and then to thelamellar crystalline phase for a 30%hydrated sample. In the more hydrated

samples, a cubic-to-cubic phasetransition (Pn3m to Ia3d) was observed.The crystalline phase is the only onethat survives above 3 kbar.

While the crystalline phase is foundto be incompressible, the unit celldimensions of the cubic and thelamellar Lα phases increase as afunction of pressure. The monolayerthickness, the cross-sectional area permolecule, and the mean and gaussiancurvature [3], as a function of pressureand composition derived from thesedata, are summarised in Figure 4. Theobserved behaviour clearly indicatesthat the pressure induces a continuouschange in the shape of monooleinmolecules. In the cubic phases, thesechanges imply the stretching of thehydrocarbon chains and the consequentreduction of their cross-sectional area,resulting in the decrease in the meancurvature at the polar/apolar interface.These deformations are clearly involvedin the associated curvature elastic

Fig. 2: Typical 2-Ddiffraction patternsfrom a cubic Ia3dphase at a pressure of1.1 kbar and 28 wt.%of water.

Fig. 3: Azimuthallyaveraged diffractionpatterns at different

pressures for a sample of30 wt. % water.

Fig. 4: Structural parameters deduced fromthe diffraction data as a function of pressurefor a sample containing 30 wt.% of water.

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energy contributions to the cubic phasefree energy which explains the observedphase behaviour.

Starting from the Helfrichdescription [3,5] for the curvatureelastic energy, the ratio of themonolayer gaussian bending constant tomean-curvature bending constant kG/kand the spontaneous curvature H0 (thecurvature that the monolayer wouldassume if it were free from all otherconstraints) were determined in thePn3m and Ia3d cubic phases by anumerical fit of structural data obtainedat different pressures. The pressuredependence of the spontaneouscurvature and of the ratio kG/k havebeen determined for the first time.Despite ignoring (or assuming only aminimal change across the phasetransition at constant pressure) the chainpacking and other contributions likeinterlamellar interactions, the curvaturemodel provides the proper location andstability of each cubic phases withrespect to the others, both as a functionof pressure and concentration. For thesake of illustration, the recalculated freeenergy of Pn3m and Ia3d cubic phasesas a function of concentration atconstant pressure and as a function of

pressure at constant concentration areshown in Figure 5. The arrow indicatesthe point at which the phase transitionwas observed experimentally. The goodagreement demonstrates how well thistype of experiment can provide aquantitative test of theories on stabilityand energetic of lyotropic phases.

REFERENCES

[1] H. Chung, M. Caffrey, Nature, 386, 224-226 (1994).[2] P. Mariani, B. Paci, P. Bosecke,C. Ferrero, M. Lorenzen, R. Caciuffo, Phys.Rev. E, 54, 5840-5843 (1996).[3] W. Helfrich, J. Phys.: Condens. Matter, 6,A79-A92 (1994). [4] C. Toprakcioglu, in TheoreticalChallenges in the Dynamics of ComplexFluids, ed: T. McLeish, Kluwer Academic,p 235 (1997).[5] R.H. Templer, D.C. Turner, P. Harper,J.M. Seddon, J. Phys. II (France), 5, 1053-1065 (1955).

ACKNOWLEDGEMENTS

The ESRF chemistry laboratory(H. Müller and co-workers) isacknowledged for the synthesis ofmonoolein compound.

Pn3m

Ia3d

Pn3m

Ia3d

P = 0.9 kbar

Cwat = 38 % (w/w)

Cwat % (w/w)

Pressure (kbar)

0.0 0.5 1.0 1.5 2.0 2.5

2.0 10–3

1.6 10–3

1.2 10–3

8.0 10–4

4.0 10–4

Scal

e fr

ee e

nerg

y pe

r m

olec

ule

5.6 10–3

4.0 10–3

2.4 10–3

8.0 10–4

Scal

e fr

ee e

nerg

y pe

r m

olec

ule

0.20 0.30 0.40

Fig. 5: Scaled free energy for thePn3m and the Ia3d cubic phases as afunction of concentration at constantpressure (P = 0.9 kbar) and as afunction of pressure at constantconcentration (38% w/w of water).

pub appliedgeomechanics

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A

GENERATION OF SHORT PULSES OF HYDROXYL RADICALS BY

SYNCHROTRON RADIATION FOR TIME-RESOLVED HYDROXYL

RADICAL FOOTPRINTINGM. ROESSLE1, E. ZAYCHIKOV1, L. DENISSOVA1, M. WULFF2, F. SCHOTTE2, M. HANFLAND2, B. SCLAVI3, C. BADAUT3,

M. BUCKLE3 AND H. HEUMANN1

1 MAX-PLANCK-INSITITUT FÜR BIOCHEMIE, MARTINSRIED (GERMANY)2 ESRF3 INSTITUTE PASTEUR, PARIS (FRANCE)

Short pulses of hydroxyl radicals can be generated by synchrotron radiation and used to follow

biological processes at time intervals on the millisecond scale.

key process of the cell is thetranscription of the genetic informationencoded in the DNA. This process isfacilitated by the enzyme DNA-dependent RNA polymerase (RNAP),which moves along the DNA “reading”the DNA sequence and synthesising abase-complementary RNA. We intend touse hydroxyl radicals (OH•) in order tofollow the movement of RNAP on theDNA in the millisecond range. Hydroxylradicals cleave the DNA at those regionswhich are not covered by the RNAP. Dueto the ionising property of the X-raybeam, high-intensity X-ray pulses can beused to produce short hydroxyl radicalpulses which can cleave the DNA in thesame manner as chemically generatedhydroxyl radicals (Figure 1a).

The DNA is cleaved withoutsignificant base specificity (Figure 1b)by interaction of the hydroxyl radicalswith the sugar moiety. Those regions onthe DNA that interact with the protein areprecluded from hydroxyl radical attackand appear in the gel electrophoreticpattern as windows (footprints) inthe otherwise regular cleavage pattern(Figure 2). The cleavage pattern isvisualised by autoradiography of theradioactively-labelled fragments whichare electrophoretically separated – aprocedure similar to DNA sequencing.

Hydroxyl radicals are routinelygenerated chemically by the Fentonreaction and are used for probing protein-DNA contacts. The rate-limiting step inthis footprint reaction is the productionof hydroxyl radicals. In the Fenton

reaction the rate of chemically producedradicals is to low for fast footprinting.The integral amount of radicals forsufficient cleavage is reached after severalseconds. Therefore, the time interval forsubsequent footprints is limited to 20seconds. Using the white beam of the X-ray synchrotron spectrum at ESRF’s ID9

beamline, it is possible to generate shortpulses of OH• which enables footprintingat 10 millisecond intervals by increasingthe rate of Hydroxyl radical production bya factor of 104.

Figure 2b shows a schematic footprintof RNA polymerase bound specifically to

Fig. 1: a) Productionof hydroxyl radicals

(OH•) by ionisingradiation, b) Cleavagereaction of the DNA-

backbone afterhydrogen abstraction

at the C4'-atom by theelectrophilic, highly

reactive hydroxylradical.

Fig. 2: Scheme of DNA-footprinting. a) The bound

protein covers regions onthe DNA and protects

them from cleavage, b)This protected and

therefore uncleaved regionremains as missing bandsin the cleavage pattern onthe autoradiographic gel.

a)

b)

a) b)

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its cognate DNAfragment. The followinginformation can be extracted from thehydroxyl radical footprinting patterns:• The size of the DNA region interactingwith the protein, which is obtained fromthe positions of the windows.• The mode of interaction, which can bederived from the variation of the intensityof the bands within the interacting region.Protection of both strands indicates thatthe protein wraps around the DNA,whereas a window at both strands shiftedby 10 bases indicates protein bindingtowards one side of the DNA.

In order to obtain quantitative dataabout the interaction of DNA and protein,the exposure time has to be adjusted insuch a way that not more than 10 - 20% ofthe DNA molecules are cut. A simplecriterion for the quality of the cleavageprocedure is a linear increase in the bandintensity with the exposure time. Thislinearity is demonstrated for our cleavagestudies in Figure 3.

Cleavage by hydroxyl radicals occursnot only in the DNA but also in theprotein. However, this does not interferewith the interpretation of the footprintingdata, since the DNA is cleaved muchmore efficiently than the protein due to itshigher sensitivity towards the hydroxylradical. Only the DNA fragments whichare cleaved by hydroxyl radicals producethe characteristic band pattern on theelectrophoresis gel. Direct strain breaks ofthe DNA-helix due to radiation damagewould produce DNA fragments of everysize and lead to a strong background onthe gel. Therefore the exposure time hasto be adjusted to obtain good cleavagewith minimal radiation damage.

In order to follow the movement ofthe RNA polymerase along the DNA, thefootprints have to be determined in themillisecond time range. One prerequisiteis rapid mixing of the components, whichis achieved by a fast mixing device havinga dead-time below 20 ms. The machineconsists of a system of syringes andproduces a continuous flow of mixedsample through the irradiated capillary.A stepping motor controls the flow-rate,permitting a minimal exposure time of0.5 ms/µl. This device was installed at theID9 beamline using the wiggler (gap at30 mm) without any beamline optics. The

sample was irradiated with a 2.5 x 1 mm2

beam using a quartz capillary (OD 1 mm;walls 0.01 mm). Damage to the capillarywas avoided by using glassy carbon andaluminium attenuators.

Figure 4 shows the first footprint ofRNA polymerase obtained by X-raysynchrotron radiation in 10 ms. On thegel, the protected regions are visible asareas with less pronounced or missingbands (Figure 4a). The larger regionindicates the full protection of the DNAby the protein and the smaller regionsabove, separated by windows of ~10base-pairs, the half protection of theDNA. Further analysis of the patternis done by integrating the profile ofthe pattern (Figure 4b). In the profilethe protected regions, compared tounbound DNA are shown. The patternis compatible with that obtained bychemically generated OH-radicals after20 s.

Potential applications of thefootprinting technique include theanalysis of the structural rearrangementsof RNA polymerase and DNA duringformation of the transcription competentinitiation complex. During formation ofthis complex at least three differentintermediate complexes are transientlyformed, namely the closed complex,

Fig. 3: Linearincrease incleavage withexposure time;the solid lineindicates thepercentage ofcleavage usingchemicallygeneratedhydroxyl radicalsafter a reactiontime of 1 minute.

Fig. 4: Footprint of the RNA-polymerase on the DNA. a) Experimental data: Upperpattern RNA-polymerase + DNA; lower pattern DNA alone, as reference, b) Profileanalysis of the cleavage pattern from a).

a)

b)

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the intermediate complex and thetranscription competent open complex.These intermediates are characterised bykinetic studies and by chemicalfootprinting. The later required loweringof the temperature in order to “freeze”the intermediate complexes. FastFootprinting by synchrotron-generatedhydroxyl radical pulses would allowdirect structural characterisation of theintermediates.

Another fascinating application ofthis technique would be the analysis ofthe formation of initiation complexeswhich are controlled by helper proteins

such as the Fis-protein. These helperproteins play an important role for thecontrol of gene expression not only inbacteria but also in eucaryotic cells.

A related project which could alsobe tackled by Fast Footprinting is theanalysis of the translocation of RNApolymerase along DNA during thetranscription process in real time –a “cinematographic” analysis. Thisprocess is probably not monotonousand does not occur in parallel withincorporation of each nucleotide intothe RNA. The latter process occursapproximately every 50 - 500

milliseconds. In order to follow thisprocess in real time, Fast Footprintingusing synchrotron-generated OH-radicals is presently the only directapproach to follow the movementof the enzyme on the DNA.This translocation process recentlygained special attention, since RNApolymerase can be considered as ahighly processive linear molecularmotor.

ACKNOWLEDGEMENTS

We thank the DFG for support.

pub Goodfellow

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A

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transmission X-ray microscope(TXM) for the photon energy range of3-7 keV has been installed on the ID21beamline. The optical scheme of theTXM (Figure 1) is analogous to that ofa visible light microscope where theincident radiation is condensed onto theobject and a magnified image of thesample is formed by an objective lensonto a spatially resolving detector. Zoneplates are used as the condenser andimaging objective optics [1]. Whencompared to a TXM for soft X-rays, themajor difference is that the setupfor spectro-microscopy applicationsincludes a Si monochromator with anenergy resolution of about 10–7 [2].The other difference is a consequenceof the low emittance of insertiondevice sources at third generationsynchrotrons; the low numericalaperture illumination makes it difficultto use a condenser as the unique beam-condensing element. To overcome thislimitation, a rotating two-mirrorassembly can be introduced into the

condenser system to match thenumerical aperture between thecondenser and the imaging objectiveand to generate quasi-incoherentillumination [3,4]. The strategy adoptedfor the ID21 TXM was to favourmechanical stability for sub-100 nmspatial resolution imaging by keepingthe design compact. The microscope’sconstruction is highly modular andreadily adaptable to different imagingmodes. This approach allows sufficientspace to be reserved for a varietyof sample stage environments and,in particular, will allow laterimplementation of specialised stages fortomographic and cryogenic imaging.

To illustrate the imaging capabilitiesof the microscope, a customised testobject was manufactured. The 400 nm-thick Au object was a variable line-spacing grating with line widths fromabout a micrometre down to 85 nm. Thegrating was imaged using an Au micro-zone plate with an outermost zone

width of 70 nm. Both test object andmicro-zone plate were generated at theInstitute for X-ray Physics (IRP),Goettingen, Germany [5]. The 1 mm-diameter Au condenser zone plate wasfabricated at the IESS/CNR, Rome,Italy [6] and has a diffraction efficiencyof 19%. Figure 2 shows an absorptioncontrast X -ray image of the Au gratingwhich was acquired at a photon energyof 4 keV with an exposure time of 1 s.The smallest lines of 85 nm can clearlybe resolved with good contrast - this isthe best performance reported for such amicroscope at these energies.

X-RAY IMAGING WITH SUB-100 NM SPATIAL

RESOLUTION AT 4 KEVB. KAULICH, R. BARRETT, M. SALOMÉ, S. OESTREICH AND J. SUSINI

ESRF, EXPERIMENTS DIVISION

The ID21 transmission X-ray microscope is an instrument which, in addition to offering

the opportunity for sub-100 nm imaging with exposure times in the second and minute

range, extends the imaging technique to spectro-microscopy applications thanks

to the specific design of its monochromator.

Fig. 1: Optical scheme of the transmission X-ray microscope at the ID21 beamlinewith the low bandpass filtering double mirror (MO), the beam-steering multilayer(ML), a channel-cut monochromator (CC), a large diameter zone plate (CZP) whichcondenses the beam onto the sample (SAM), and a micro zone plate (MZP) whichproduces a magnified image at the detector (CCD).

Fig. 2: High spatial resolution X-rayimage of an Au test grating with varyingline width from a few micrometres downto 85 nm. The image was taken at aphoton energy of 4 keV, the exposuretime was 1 s. The smallest structures of85 nm can clearly be resolved with goodcontrast.

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The feasibility of spectro-microscopy was demonstrated byimaging concrete samples. A series of ahundred images was taken across the CaK-edge (4038 eV), with energy steps of0.6 eV and 30 s exposure time. The flat-field corrected images were aligned andorganised in a three-dimensional arrayor energy stack, allowing quick accessto the spectrum of any region of interestin the image (Figure 3).

The microscope is now being usedfor a wide variety of applications. It issuitable for the use of complementaryimaging modes like absorption, Zernikephase or interference contrast. It offersthe possibility of near-edge absorptionstudies for elemental mapping andanalysis of the chemical states of thesample with sub-100 nm spatialresolution within the 3-7 keV energyrange.

REFERENCES

[1] B. Kaulich, T. Wilhein, S. Oestreich, E. DiFabrizio, M. Gentili, P. Charalambous,M. Salome, R. Barrett, J. Susini, Appl. Phys.Lett., 75, 1328 (1999).[2] S.Oestreich, B. Kaulich, J. Susini, Rev.Sci. Instrum., 70, 1921 (1999).[3] B. Niemann, in X-ray microscopy andSpectromicroscopy, J. Thieme et al. (eds.),Springer Verlag, IV-45 (1998).[4] S. Oestreich, G. Rostaing, B. Niemann,B. Kaulich, M. Salome, J. Susini, R. Barrett,in 6th International Conference on X-raymicroscopy, W.Meyer-Ilse, T.Warwick,D.Attwood (eds.), AIP Proceedings (Berkeley,Aug. 1999), vol. 507.

[5] M. Panitz, G. Schneider, M. Peuker,D. Hambach, B. Kaulich, S. Oestreich,J. Susini, G. Schmahl, in 6th InternationalConference on X-ray microscopy, W. Meyer-Ilse, T. Warwick, D. Attwood (eds.), AIP

Proceedings (Berkeley, Aug. 1999), vol. 507.[6] E. Di Fabrizio, L. Grella, M. Baciocchi,M. Gentili, L. Peschiaroli, L. Mastrogiacomo,R. Maggiora, J. Vac. Sci. Technol., B 14, 3855(1996).

ACKNOWLEDGEMENTS

The authors thank L. André, R. Baker, P. Bernard, G. Berruyer, A. Koch, F. Demarcq,D. Fernandez, P. Noé, S. Ohlsson, D. Rolhion, G. Rostain, M. Soulier, F. Thurel, andH. Witsch for their invaluable technical assistance and contributions. Theperformance of this microscope benefits from the high-quality phase zones platesproduced by E. Di Fabrizio, M. Panitz and P. Charalambous. The conception of themicroscope was aided greatly by many hours of fruitful discussion with manycollaborators, especially B. Niemann, G. Schneider, T. Wilhein, and W. Meyer-Ilse.

a)

b)

Fig. 3: X-ray spectro-microscopy: (a) Two sections of an energy stack of X-ray images of a

concrete sample after the Ca K-edge, (b) the CaCO3 spectrumrecovered from a region of interest through the image stack.

VACANCIES AT THE ESRF ON 20 SEPTEMBER 2000

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IN-VACUUM UNDULATORSP. ELLEAUME, J. CHAVANNE AND P. VANVAERENBERGH

ESRF, MACHINE DIVISION

Following the successful operation of a prototype in-vacuum undulator on ID11, the ESRF has

started the production of 4 in-vacuum undulator segments, of 2 m in length and with periods

between 17 and 23 mm.

NTRODUCTION

The magnetic gap of undulators andwigglers, as for any other acceleratormagnet (dipole, quadrupole,…), is adesign parameter of major importance.The smaller the gap, the lower thecurrent or the smaller the volume ofmagnetic material (permanent magnetor steel) needed to reach a givenmagnetic field. In the case ofundulators, a reduction of the gap alsoallows a reduction of the spatial periodwhich results in a shift of the radiationspectrum to higher energies. This is ofprime interest in a number of scientificapplications. In the classical andsimplest approach, one uses a fixed-gapvacuum chamber and places the magnetblocks in the air outside the vacuum. Atthe ESRF, the smallest aperture left to

the electron beam (beam stay-clear) isaround 5-6 mm if one does not want toreduce the lifetime of the stored beam(see below). When taking into accountthe thickness of the chamber wall, theflatness and position errors, the result isa minimum gap in the range of 10-11mm. So far the majority of ESRFbeamlines are equipped with a 15 mm-thick chamber which permits aminimum gap around 16 mm. The first10 mm chambers have met themechanical specifications but the lackof distributed pumping has not alloweduser operation for lengths exceeding 2m. This is due to the Bremsstrahlunggenerated by the collision of theelectrons with the residual gas. One wayto avoid these difficulties is to place thepermanent magnet blocks in thevacuum of the ring (in-vacuum

undulator). This allows a minimum gapalmost identical to the beam stay-clear.The idea of in-vacuum undulators canbe traced to the early 1980’s with aninstallation on the NSLS [1] ring andlater BESSY [2]. The technology wasre-examined with the installation ofa 3.6 m-long device at the photonfactory [3]. Then a real advance tookplace with the large-scale engineeringdevelopment made at SPRING-8 [4].SPRING-8 is presently operating morethan 15 in-vacuum undulators each witha typical length of 4.5 m and a 30 m-long in-vacuum undulator is also underconstruction. Recently a short in-vacuum undulator (0.32 m) wasinstalled at the NSLS [3]. The recordminimum gap is 3.3 mm with a 10%lifetime penalty. Such a small gap isonly possible due to the short length of

I

Fig. 1: Prototype in-vacuumundulator installed on the

ID11 beamline.

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undulator which allows the use of asmall vertical beta function. Assumingan optimised beta function, the smallestgap achievable scales with the squareroot of the length of the undulator. Forreasons of cost and resources, thedevelopment at the ESRF of thistechnology only started four years agowith the testing of a prototype Spring-8undulator [6] followed by theconstruction of a prototype device [7].We are now embarking on a large-scaleprogramme of construction of such in-vacuum undulators. One should alsomention that several new facilities ofmedium energy (Swiss Light Source,Canadian Light Source, AdvancedLight Source ..) have chosen to buildsuch in-vacuum undulators. Althoughthey used to be considered a specialisedand risky technology, in-vacuumundulators are now becoming muchmore common.

EXPERIENCE WITH THEESRF PROTOTYPE

The prototype in-vacuum undulatorin operation on ID11 is 1.6 m long witha period of 23 mm, and with a peak fieldhigher than 1.1 T at the minimumoperation gap of 5 mm. Figure 1presents a 3-D view of the undulator,

the support, the tank and pumpingsystem. This undulator was designedto operate with the smallest gap thatwould be compatible with an acceptablereduction of the lifetime. Consequently,a significant number of the electronslost in the ring are likely to hit thepermanent magnet material. In view ofthe partial demagnetisation that wasobserved in 1993 on two conventionalundulator segments (following a mis-steering of the booster beam), it wasdecided to use Sm2Co17 material forthe magnet blocks. The reduction ofthe field as a consequence of the useof Sm2Co17 instead of NdFeB isequivalent to a 1 mm gap difference.A large pumping capacity was madeavailable to the tank (860 l/s ion pump& 2000 l/s of titanium sublimation). Asa result no measurable Bremsstrahlungcould be observed on the beamline forany gap larger than 4.5 mm. Figure 2presents the measured reduction oflifetime as a function of the magneticgap in the 2 x 1/3 filling mode (200 mA)and 16 bunch mode (80 mA). Nomeasurable lifetime reduction can beobserved above 6 mm, however, a 5%lifetime reduction is recorded at 5 mm.Before the installation of this undulator,ID11 was operating a 1.2 T wiggler witha 125 mm period of the same length.The field was not shimmed due to a lack

of time. Despite this, the new undulatorproduced more flux per unit surface atthe primary slit for all energies below70 keV, which has made the wiggleralmost completely obsolete.

ENGINEERINGDIFFICULTIES

Several engineering difficulties(vacuum, mechanical and magnetic)were encountered in the production ofin-vacuum undulators. As all magnetsmust be coated to limit the degassing inUHV, nickel plating was used whichresulted in a 9x10-11 static vacuumafter bake-out at 120°C. Additionally,the magnets must be covered with acontinuous conducting sheet (copper) tolet the return current flow freely withoutheating the magnets. Continuity at theexits of the undulator must also beensured. These exit transitions (calledRF-Fingers) need to be flexible to allowa gap change in the range of 5-30 mm.Their perturbation on the beam isquantified in terms of an impedancewhich produces local heating (real partof the impedance) and is responsible forbeam instabilities (imaginary part of theimpedance). The highest temperaturerecorded on the prototype was 120°C atthe junction between the RF-finger andthe magnets. The connections betweenthe upper and lower rigid girders (openair) and the magnet assemblies (in-vacuum) are made by 8 columnssurrounded by bellows that mustoperate for a large number of cycleswithout leaking. Finally, the procedurefor magnetic measurement andshimming had to be significantlymodified because of the lack of lateralaccess for a Hall probe when themagnets are "in-vacuum".

FUTURE

The ESRF is presently embarking onthe manufacture of four new in-vacuumundulator segments, each 2 metres-longwith periods of between 17 and 23 mm.In view of the extra space required forthe RF-fingers, the segment length hasbeen increased from 1.6 m to 2 m inorder to accommodate a maximumnumber of two segments. In the longerterm, the manufacture of more in-vacuum undulators will be linked to theavailability of 10 mm fixed gapchambers with a proper dynamic

Fig. 2:Measuredlifetime as afunction of themagnetic gap ofthe prototypein-vacuumundulator.

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vacuum. There are two main reasonsfor the use of in-vacuum undulators atthe ESRF: Firstly, for a given K value(imposed by the tunability), an in-vacuum undulator can be built with asmaller period and a correspondinglyhigher photon energy of the fundamentaland harmonics. This is of importance forbeamlines where high brilliance at highphoton energy is required. This isillustrated in Figure 3 which comparesthe ultimate brilliance of two fullytunable undulators with K=2.2, a 4 mlong U28 in-vacuum operated with aminimum gap of 6 mm and a 5 m longU42 undulator with a minimum gap of16 mm. The gain in brilliance is notsignificant at low energies, however, itgrows very rapidly above 20 keV.Secondly, full tunability is not essentialfor a few ESRF beamlines, and inpreference they are optimised formaximum flux on the fundamentalaround 12-14 keV. In-vacuum undulatorsare also well suited for such applications,this is illustrated by Figure 4.

As discussed earlier, in-vacuumundulators can compete with wigglers(ID11) due to their high field. Indeed,not all wiggler beamlines can benefitfrom such undulators since they have avery small divergence and arenevertheless limited in field andtherefore in critical energy. Very highfield wavelength shifters are far frombeing obsolete. The question has beenraised of whether it is possible to buildhard X-ray rings at 4-5 GeV morecheaply than the present 6-8 GeV ringsby making extensive use of in-vacuumundulators instead of open-airundulators. This is partly true, but oneshould not forget that reducing theelectron energy of a low emittance ringhas a serious impact on the lifetime andthe stability of the beam.

REFERENCES

[1] H. Hsieh, S. Krinsky, A. Luccio,C. Pellegrini, A. Van Steenbergen, Nucl. Instr.and Methods, A208, 79-90 (1983).[2] W. Gudat, J. Pfluegher, J. Chatzipetros,W. Peatman, Nucl. Instr. and Methods, A246,

50-53 (1986).[3] S. Yamamoto, T. Shioya, M. Hara,H. Kitamura, X. Zhang, T. Mochizuki,H. Sugiyama, M. Ando, Rev. Sci. Instrum., 63,400 (1992).[4] T. Hara, T. Tanaka, T. Tanabe,X.M. Marechal, S. Okada, H. Kitamura, J.Synch. Rad., 5, 403-405 (1998).

[5] P.M. Stefan et al., J. Synch. Rad., 5, 417-419 (1998), see also P.M. Stefan et al., Nucl.Instr. and Methods, A412, 161 (1998).[6] T. Hara et al., J. Sync. Rad., 5, 406-408(1998).[7] J. Chavanne, P. Elleaume, P. VanVaerenbergh, Proc. of the 1999 ParticleAccelerator Conference, p. 2662.

ACKNOWLEDGEMENTS

The authors would like to thank B. Plan from the Drafting Office who supervised the mechanical design work andR. Kersevan, M. Hahn, D. Schmied of the Vacuum Group for the design and handling of the vacuum equipment and also theAlignment Group.

Fig. 3: Brilliance comparison between two fully tuneable undulators(K = 2.2) at a gap of 16 mm and 6 mm.

Fig. 4: Comparison of spectral flux in the fundamental for a 16 mm gap and6 mm gap undultor. These undulators have a limited range of tunability andthe period is optimised for a maximum flux around 1 Angstrom.

The ESRF Newsletter is published by the European Synchrotron Radiation FacilityBP 220, F38043 Grenoble cedex

Editor: Dominique CORNUÉJOLS Tél (33) 4 76 88 20 25Dépôt légal : 4eme trimestre 2000. Printed in France by Imprimerie du Pont de Claix. Layout by Pixel Project.