LA-UR- &’J -5345

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Title: PROGRESS IN DESIGN OF THE SNS LINAC

Author(s): Roabert Hardekopf, SNS-DO

Submitted to: International Congress Center (ICANS Meeting)November 6-9, 2000, in Epochal Isukuba, Japan

.:..,

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ICANS-XV15ti Meeting of the International Collaboration on Advanced Neutron Sources

November 6-9,2000Tsukuba, Japan

Progress in Design of the SNS Linac

R. Hardekopf 1“for the SNS linac design teaml

J Los Aamos National Laboratory, Los Alamos, NM, 87545, USA* E-mail: hardekopf @Ian] .EOV

Abstract

The Spallation Neutron Source (SNS) is a six-laboratory collaboration to build an intensepulsed neutron facility at Oak Ridge, TN. The linac design has evolved from the conceptualdesign presented in 1997 to achieve higher initial performance and to incorporate desirableupgrade features. The linac will initially produce 2-MW beam power using a combination ofradio-frequency quadruple (RFQ) linac, drift-tube linac (D’I’L),coupled-cavity linac (CCL),and superconducting-cavitity linac (SCL). Designs of each of these elements support thehigh peak intensity and high quality beam required for injection into the SNS accumulatorring. This paper will trace the evolution of the linac design, the cost and performance factorsthat drove architecture decisions, and the progress made in the R&D program.

1. Introduction

The SNS project had its conceptual design review in June 1997 and received constructionfunding from the US Department of Energy in October 1998. The original design of the 1-GeV linear accelerator (linac) was a room-temperature device that could deliver averagebeam currents from 1 to 4 mA to the accumulator ring that follows. The bd@ine designwould have provided 1 MW of beam power, but the accelerator system was upgradeable to 2and 4 MW. This design and the upgrade requirements were described in several early papers[14]. “l’herequirements and design teatures. . ..—. . . . .

are shown in Tables 1 and 2.

Table 1. Linac requirements at CDR

Input H_energy 2.5 MeV

Output H- Energy 1001 MeV

Average beam current 1.04mAAverage beam power 1.04 MwMacropulse repetition rate 60 HzMacropulse length 0.974 ms

Beam duty factor 5.84 %Chopper transmission 65%Chopper period 841 nsPeak macropuise current 27.7 mAAvg. macropulse current 18.0 mABeam 10sW% <1 nA/mat 1 OeV

Table 2. Original linac design parametersRf duty factor 7.02%A;erage accelerating gradient&T 2.7 MV/mAvg.’Energy gain / real estate meter 2.02 MeV/mPeak structure power 10ss4s 80.7 MWPeak rf power 98.7 MWAverage rf power to linac 6.74 MWSpecified ac wall power for rf 22 MwNo. of 1.25-MW 402.5-MHZ tdJ%&OtlS 2No. of 2.5-MW 805-MHz klystrons 56Physical length of Iinac 495 mLlnac vacuum <1 x 10-7torrLinac tunnel, width x height 14xloft

~~~~f~~~

WC t32000

OSTi

The evolution of the CDR design has been described []. ‘The 2-MW upgrade could beachieved with only the addition of RF power, but 4 MW requhed a second ion source and402.5-MHz front-end system up to 20 MeV, with funneling of the two beams into an 805-MHi Structure.

Following an intensive project review late in 1999, the baseline design was changed to a 2-MW accelerator without provision for upgrading to 4-MW. This allowed us to eliminate oneof the RF structures, the CCDTL, by extending the 402.5-MHz DTL up to about 86 MeV. Atthis energy, the beam could be injected diwtly into the CCL structure. This change wasformally adopted in November, 1999. The following March, following a technical and coststudy of superconducting technology applied to this project, the baseline changed to asuperconducting RF linac (SRF) beginning at 186 MeV. Subsequent optimization of thisdesign has led to the configuration in Figure 1 with overall pararnetem in Table 2.

402.5 MHz 805 MHz

4 b 4 b

IHRFQ DTL CCL SRF, 6=0.61 SRF$fi=O.81 ‘EBT To

4 t Y +~ t

Ring

lnjJctor 2.4 MeV 86.8 MeV 186 MeV 375 MeV 972 MeV

Figure 1. Layout of the present SNS Linac. The RFQ, DTL, and CCL are warm structures,and the two SRF regions are superconducting. The numbers are energies at the end of eachstructure.

Table 3. Parameters of key components for superconducting linac (SCL) baseline, Oct. 2000Component Units 2-MWvalueH- ion source Peak current 65mA2.5-MeV RFQ Peak current 52 mAFast choppe rs – 2 (chopper & antichopper) Beam-on duty factor 68%86-MeV, 402.5-MHz DTL tanks 6“186-MeV, 805-MHz CCL RF modules :.,4350-MeV, beta=O.61 SRF in 11 cryostats RF modules ’331000-Mev, beta=O.81 SRF in 15cryostats RF modules 59402,5-MHz, 2.5-MW klystrons (incl RFQJ number 7805-MHz, 5.O-MW klystrons (incl. HEBT) number 6805-MHzz, 550-kW klystrons number 92Total installed RF peak pOWer 93

“,,..

Because of project cost constraints, the energy of the linac will initially be slightly less than 1GeV, but space is provided in the linac tunnel to increase the energy by adding additionalSRF sections. Depending on SRF cavity performance and addition of more RF power, anenergy of 1.2 GeV or higher could be achieved, allowing a possible second target stationwhile maintaining 2 MW on the first target. The following sections describe the currentdesign status.

2. Front-End System and Chopper

The front-end system, including the H- ion source (65 keV), RFQ linac (2.5 MeV), andmedium-energy beam transport (MEBT) is being designed and built by Lawrence Berkeley

,r

L&mitory, one of the partners in the SNS collaboration. This injector, most recentlydescribed in [4], will deliver a chopped, high-brightness H- beam to the DTL with peakintensities of 52 mA.

A key requirement of the linac and accumulator ring design is the ability to cleanly chopbeam to provide a gap in the stored beam in the ring for extraction. Because SNS will

the

operate at higher peak intensities than any exisitng spallation source, forming this gap andkeeping it clear of particles at a level less than 104 of the peak beam is critical for reducingradiation levels in the ring and subsequent activation of ring components. We are designing atraveling-wave chopper based on the experience at LANSCE, but operating at higher voltagebecause of the 2.5-MeV beam from the RFQ. Table 4 lists the specifications.

Table 4. MEBT choppe r requirements

Beam Energy 2.5 MeVChopper length 35 cmChpper gap 1.8 emVoltage * 2.35 kVDeflection angle 18 mradChopping period 945 nsRise & fall time <10 ns

Figure X. General construction of MEBT chopper on the left with scope trace on the rightshowing -2 ns risetime demonstrated on a proof-of-principle structure.

Figure X shows the meander-line structure currently being developed under the linac R&Dprogram. Performance of the prototype has matched the 3D MAFIA calculations,demonstrating a 50-ohm structure with a risetime of 2 ns. The actual risetime will be limitedby the FET pulsers, currently under development at DEI, Inc. in Boulder, CO. Thespecification for two pulsers to drive the top and bottom meander lines is t 2500 V with 10-ns (5 to 95~0) risetime. Since with this risetime, partially deflected micropulses of the 402.5 -MHz beam will be transmitted, an anti-chopper is provided in the MEBT to return thesemicropulses to the beam axis before entering the DTL.

Figure 2. Meander-line structure for the fast MEBT chopper. The proof-of-principlestructure is orI the lefi and a closer view of the etched copper striplines is on the right.

3. Drift-Tube Linac (DTL)

The DTL parameters are summarized in Table 5.

Table 5. DTL Design parameters

Parameters DTL

Structure frequency (MHz) 402.5Energy (MeV) 86.8Physical length (m) 36.5Bore radius(cm) 1.0Focusing lattice FFODDOLattice period length 4pAAccelerating gradient Eo (MV/m) 3.0Synchronous phase (deg) -30Ave. acceleration rate (MeV/m) 2.01Peak RF power (MW) 15

The DTL is divided into 6 tanks, or RF modules. Figure 2 is a cutaway view of the first DTLtank.

Fig. 3. Cutaway view of DTL tank 1 as presented at the Sept. 27 PDR.

Each tank is composed of two or three sections along the length that are fastened togetherusing metal seals at the interfaces. The structures consist of copper-plated steel tanks withcopper drift tubes mounted on stainless-steel stems. One 2.5-MW klystron powers each tankand each tank has a separate water-temperature-based resonance-control loop. Permanent-magnet quadruples (PMQs) are arranged in a FFODDO lattice, which allows placement ofelectromagnet steering and beam-position diagnostics within the “O” drift tubes. Each tankhasa minimum of 4 steering magnets. The inter-tank regions contain additional diagnosticcomponents including profile measuring scanners and current sensors. Post couplers are usedat every third drift tube to stabilize the field and to generate a ramp in the first tank forlongitudinal matching of the beam from the RFQ and MEBT. Fig. X is a photograph of alow-power cold model currently being tested for RF properties

Fig. X. Cold model assembly for SNS DTL Tank #1.

A preliminary design review of the DTL was held in September 2000, and final design andfabrication are underway, with delivery of the first module scheduled for 2002.

4. Coupled-Cavity Linac (CCL)

The CCL accepts beam from the DTL at 87 MeV and delivers it to the SRF linac at about186 MeV. The basic parameters are shown in Table 6.

Table 6. CCL Design parameters

Parameters CCL

Structure frequency (MHz) 805Final energy (MeV) 185.6Number of RF modules 4

Number of segments per module 12

Number of cells per segment 8

Physical length (m) 55,36

Bore radlus(cm) 1.75 [0 2.00Focusing lattice FODO

Lattice period length 13(3AAccelera(lng gradient EO (MV/m) 3.38 (O 3.66

Synchronous phase (deg) -30to -24Ave. acceleration rate (MeV/m) 2.17Peak RF-structure-power (m 20

Bridge couplers between segments are 3-cell structures of length 2.5 ~k withRF-feeds through the center cell of the bridge coupler at the 1/4 and 3/4 points of eachmodule. The total thermal load -1.1 MW at an operational temperature -80 F. Quadruplefoeusing magnets and beam diagnostics are located in the spaces between the segments, andare supported off the main girder separately from the cavities. Modules will be assembled ina staging area, tuned and subjected to a series of acceptance tests. When completed, themodules are parted at the central bridge coupler, moved into the tunnel in halves using anengineered transporter, and then reassembled. A series of final tests are conducted in thetunnel as well as connections to the water, RF waveguide and cabling. Figure X is anassembly drawing of one of the modules, and figure Y shows the more detail of twosegments and the coupling cavity.

,-U\ Turbomolecular Pump

-urmlu ~ *dml,upvti.tind“0”(’”’”’)Y

(2 sections):..

RF waveguide interface Segments -12 ‘:.(2 Dlaces) Length -12.1 “iheters. . .

INumber of eelts- 96Intersegment gaps - 2.5BA

Figure X. Assembly drawing of the first of four 5-W CCL modules...

uFigure Y. Two 8-cell CCL segments with a bridge coupler.

A R&D program is underway to build both low-power cold models and a powered hot modelof the CCL structures. With the cold models, we have tested the RF performance ofaccelerating cells, coupling cells and coupling slot geometry. We are currently testing thebridge-coupler geometry. Figure Z shows one of the assembled cold models on the bead-pulltest stand.

~.,.”..,

,.”.>

Fig. X. CCL cold-model assembly on the Fig. Z. Assembly of the CCL hot modelbead-pull test stand.

.%

The hot model, shown in Figure Z, will evaluate the segments and a bridge coupler at fullpower and provide verification of the manufacturing and tuning steps as well as thermalstability and vacuum performance. A frequency resonance-control water cart andprototypical vacuum system are being integrated with the hot model for testing beforecommitting to large-scale fabrication. Parts of the hot model are being fabricated, as shownin the following fi-gures,where a braze alloy is being tested.

——

Fig. X. Septum foil lay-up with 50-50,2-rnil alloy.

The CCL is nearing completion of preliminary design; with a design review scheduled forNovember 2000. Many of the manufacturing steps have been verified, and Initial definitionand packaging has been done for the inter-segment diagnostics. The procurement process forthe copper assemblies will be initiated in the fall of next year..

5. RF-Power System

To reduce the cost of the RF system, we perfomed many trade studies between number andpower of klystrons, RF transmitters, power supplies, and cavity control mechanisms. Thefinal architecture, shown in the following table, is the result of these studies.

Table X. Summary of linac RF architecture.

Total Celts Cavities No of StmctureStructure w fbul Length Mules Klystrons Length

*%Y M%eMeV m m

DTL 86.8 36.6 60 to 21 6 6 36.6

CCL 185.6 91.9 8 12 4 4 55.4SRF I 379.2 157.7 6 3 11 33 64.2SRF II 948,7 276.0 6 4 15 59 118.4

SRF upgrade 1227.6 323.4 6 4 6 25 47.3 “

HVPS KlystronStmcture H~S Power Transmitters Klystrons Power

Mw Mw

RFQ & DTL 3 107 7 2.5

CCL & HEBT 5 10 6 6 5.0

SRF I & II 8 10 46 92 0.55SRF upgrade 3 10 .,”. ””5 25 0.60

The following figure shows schematically the layout of the Iinac RF system.

Layout of Linac RF with NC and SC Modules

WQ D,’ ml CCL(1) (6) (4)

25* *W.$

rronl

CCL

1 33 1(92 :kl)

Fig. X Layout of linac RF system with N$ and SC modules

For the number and sizing of the SRF klystrons, we assumed the saturated power outputshould be 33% above the power needed by the cavity plus beam. Since losses are estimatedat 9$Z0of the output power

Microphonics and Lorentz-forces lead to frequency variations of about 300 to 400 Hz, total.This varies the cavity amplitude response by up to 9% and phase by up to 12° at themaximum. The combination of amplitude and phase variation is a loss of output capability ofas much as 12$Z0.The remaining overhead is about 1l~o, which is needed for other errors andnoise effects. :..

.;,:,,

The RF control system must maintain RF Fields to 4.5% and M1.5°. With.,one klystron percavity, we can provide one control loop around each ldystron/cavity pair. This provides thecapability to compensate for the Lorentz forces and microphonics. We considered using alarge klystron split many ways but decided that would compromised performance of controlswith may high-power phase shifters. Maintaining different synchronous phases in all cavities*

*

Table X. Arrangement of.the klystrons and power supplies

Fm

(

T

—

q ucye Klystm r NU rnf b w Currerl t4u m bMHz) p Wr IQyatro n (l(v) (A) Klysko n

MM p C&iv

Svs em

102.5 2.5 7 130 35 2

605 5 6 140 88 1

605 II0.55 92 69II12.7nor 2

with this method would have been an added difficulty. We can, however use one HV systemand RF transmitter to serve several klystrons, as indicated in the table above and thefollowing figure.

A mKlystm Gallety

.4 EEi!!!n—-—..Acceiemtor Tunnel

——. —

Fig. X. SCRF-system block diagram for Fig. X. Simplified block diagram of the0.55-MW klystrons. field & resonance control module

Because we are powering klystrons with outputs from 0.55 to 5.0 MW, two basic types ofHV systems are needed: a high-voltage version (140 kV) and a lower-voltage version (80kV). Both have a nominal 1O-MWpeak power. The LANL-designed converter-modulator isthe primary solution [x]. The design accommodates

. Three 2.5-MW, 402.5-MHs klystrons

. Two 2.5-MW, 402.5-MHz klystrons● One5-MW, 805-MHz klystron

A prototype of the converter-modulator is being assembled at Los Alamos, and testing willbegin next year. The prototype includes three IGBT switch plate assemblies and a boosttransformer. The control subsystem includes control and protection, an adap~ve feed-forward and feedback sytem, interlocks, and a programmable logic controlle~.

6. Lkac Physics and Simulations.

The design of the SRF Iinac has been a collaborativ~ effort between Los Akunos andJefferson Lab. Based on %X< 2’7.5MV/m, WP”made trade studies to determine the mostcost-effective combination of cavities, cryostats, and RF systems to achieve reliableperformance. The result was two cavity types, one optimized for a beta of 0.61 and the otherfor a beta of 0.81 A transition energy of 335 MeV maximized the final energy for a fixed-cost machine.

600

500

Em&

300

ml

. -. *+. u..-. .$ .

. .

~

-... no. .

.

Ilm~ 1156 400 656 900 1150 1400

Wwt MeV)

Fig. X. Graph of klystron (top) and cavity (bottom) power for the SCL. The solid lines arenominal values, and the dots are random distributions expected. For a large part of the SCL,the attainable energy gain is limited by the klystron power.

Linac with p, =0.61 ,and ~=0.81 Cavities

L. /0,00

0 1252S1375500625750075 &.*

w (Mev).,’. .

,.

.>

Fig. X. Normalized rrns transverse and longitudinal ernittances .aIong the linac without anyerror.

I .0

.1 -

* -

2. -‘2.s-gx .* -

i. -

2 -

.1 -

,.

““ a Quad Displacement 0.005”b: Quad Displacement 0.010”c: Quad Tilt 5.0°

(~ 3.5 mm over 8 cm)d: Tank Displacement 0.100”

Alignment errors cause the beam to be displaced from the linac axis and can magnify effectsof nonlinear fields such as multiples and gap fields. We studied the effect of errorsindividually to determine which of them contributed most to the displacement of the beam

*

.from the Iinac axis. The code L~CE was used, which repres@s the beam by an ellipsoidand tracks the centroid of the beam through the SRF Iinac. The figwe below shows theprobability distributions of the centroid excursion for four individual error cases with randomerrors picked within the following tolerance limits.

a Doublet displacement 0.010 inchb: Doublet tilt 0.010 (~ 0.06 mm over,70 cm)c: Quad tilt (wrt doublet axis) 1.OOO(* 3.5d Cavity displacement 0.050 inch

I.*

,g .7 -

g . . .

.6 ,~

g

x .* -

i. -

.?. -

.,

.50 .60

.-+ai..lw-l disohce,+ent <c.) d “2. center

mm over 40 cm)

a:b:c:d

Doublet displacementDoublet tiltQuad tilt (wrt doublet axis)Cavity displacement

Fig. 6. Probability distribution of the beam centroid excursion for different errors. Thedefinition of curves a,b,c, and d are given in the text above.

It is evident from the above set of plots that the doublet tilt error (b) is the most severe one,even with the extremely small tolerance used. To investigate the aggregate effect of all theerrors we consider three cases, one when no steering correction is made, and two other caseswith different sets of BPMs but with the same number (32) of dipole correctors. For thesesimulations, we doubled the tolerance on the doublet tilt to 0.02° (~ 0.12 mm over 70 cm)which is the best alignment tolerance the engineering staff expects can be achieved. Resultsare shown in the following figure.

:.....:.

,,,.. ..>

,‘,

maximum d*.@aw.-m.tkm) .< ham ..nter ‘

Fig. 7. Probability distribution for beam-centroid excursion8 BPMs and (c) with 16 BPMs.

for (a) no steering, (b) with only

We also studied the effect of different ways of calculating space-charge effects in the beambunch. The space-charge code SCHEF’F, a 2D code, is widely used for ion-linacapplications. It is fast, and when the transverse aspect ratio is not large (less than -2), thebeam does not show any changes when treated with 2D or 3D algorithms. As a check weused SCHEFF and PZCZWC, a 3D code [X], to transport the beam through the entire linac.Differences in the real-space distribution were not discemabl~ longitudinal phase-spacedktributions show only slight differences in the population density of particles on the edges.

,

.The figure below S!IOWS & real- and phase-space &stributions at the end of the SRF linacwith PICNIC. ‘

Coordinates at end of SN3 SC Linac, usina PIm IC uith wow xrticksI.e

.5

e.

-.5

-1.e

1 I 1 1.9(mrad) US. X( CM)

-1 .s

: -1.8M b= 3.2610 E= 6.=1 I 1 -1. e

-1.e -.5 e. .5 l.e -

.I I

y’(mrad) us. yba)I

a= e.em b= 2.2269 E= e.wt I I—

,.6 -.5 e. .5 I eI=llZ.894, Es=lZ49.lZ W, PS= -1S.1 dcg

I.e 1 1 I I l.e 1 1 I

ka) us. X(clal E-Es(W)” ‘k ;’jji~-~qis(deg ) I

-4.e ~ -1.e ~-1.e -.5 e. .5 l.e -se -2.5 e. 2.5 s.e

Fig. X. Real- and phase-space distributions at the end of the SCL with PICNIC 3D space-charge code.

7. Diagnostics and Commissioning Planning

Diagnostics are an important part of a high-intensity linac. Accurate steering and matchingof the beam are required to limit beam loss on apertures that would lead to activation andprevent hands-on maintenance, This subject has received attention recently,.,md severalreviews have been published [x,y]. A description of the diagnostic suite forithe SNS linachas also been published [z]. The following is a list of the types of dlagno$cs under design.

...

● Beam position and phase monitor (BPM)● Profile monitor (wire scanner and harp). Current monitors (toroids). Loss monitors (ionization chambers) ;”● Beam-in-gap detector (laser ionization)’ “. Phase width detector

The limited space in the low-energy regions of the linac have led to some novel applicationsof BPM technology. We plan on inserting BPMs in some of the empty drift tubes of theFFODDO lattice of the DTL and using the second harmonic of the beam frequency (805-MHz) for analysis. A prototype DTL BPM design is shown below.

. .

[1]

[2]

[3]

[4]

Feed through with n< OqterCover.

A“

r!!9-60”angl

Y

“-w II L-&A.x

OT outerp<”

P

a &i

P

Y Endcep

L FiduciFlatz

/x

J

flduddFlat

Inner Etectr#

Figure X. Assembly andexploded views of BPMtofit inside dtifttubesofthe D~.

The physics design of a diagnostic-plate for commissioning of the linac has started, with alayout as shown in the following figure. Commissioning scenarios have been developed forsetting phase and amplitude of the RF cavities [x] and for determining beam parametem.After the first DTL tank we plan to run full duty-factor beam into a 16-kW portable beamdump, but for higher-energy modules the commissioning will be limited to low duty factors.

Ilt IN+( 1 ENX%ATE I

Fig. X. Preliminary layout of Diagnostic Plate for commissioning DTL Tank 1.

References .‘s

B. R. Appleton, “The National Spallation Neutron Source,” Proceedings Of the ParticleAccelerator Conf. (PAC’97), Vancouver, BC (to be published)

SNS Conceptual Design Review, June, 1997, httu://www.oml. ~ov/-nsns/

A. Jason, “A Linac for the SNS,” Proceedings of the 1998 Linac Conference, Chicago, Aug.1998,415.

R. Hardekopf, “Linac Design for the SNSV Proceedings of the Second Intl. Topical Meetingon Nuclear Applications of Accelerator Technology, Gatlinburg, Sept. 1998, 208.

[5] R. Hardekopf, D. Stout, and T. Sutton, “Project Status of the l-GeV SNS L1nac,”Proceedings of the 1999 Particle Accelerator Conference, New York, March 1999,3597.

I

[6] J. Billen, H Takeda, T. Bhatia, “Linac RF Structures for the SNS~ PAC99, New YorkyMarch 1999.

[7] N. BuItman et al., “Mechanical Engineering of the Linac for the SNS~ PAC99, New York,March 1999.

[8] ~9~ynch, P. TaIlerico, W. Reass, SNS RF System Overview: PAC99, New York, March.

[9] S Kurennoy, J. Power, and D. Schrage, “Meander-Line Current Structure for SNS Fast Beam

[1

[1

[1

[1

[1

[1

[1

[1

[1

Chopper;’ PAC99, New York March 1999.

R. Hardekopf, “Beam Loss and Activation at LANSCE and SNSV LA-UR-99-6825, ICFAConference on High-Intensity, High-Brightness Beams, Lake Geneva, Sept. 1999 (to bepublished).

R. Hardekopf,. “Beam Diagnostic Suite for the SNS Linac~’ LA-UR-00-2282, BeamInstrumentation Workshop, Boston, May 2000 (~obe published).

S. Kurennoy, “Electromagnetic Modeling of Beam Position and Phase Monitors for SNSLinac,” LA-UR-00-28 15, Beam Instrumentation Workshop, Boston, May 2000 (to bepublished); and “Beam Position-Phase Monitors for SNS Linac~ International LinacConference, Monterey, August, 2000 (to be published).

S. Kurennoy Development of Meander-Line Current Structure for SNS Fast 2.5-MeV BeamChopper,” LA-UR-00-2814, European Particle Accelerator Conference, Vienna, July 2000(to be published); and Meander-Line Current Structure Development for SNS Fast Chopper,International Linac Conference, Monterey, August, 2000 (to be published).

J. Stovall, S Nath, H. Takeda, J. Billen, L. Young, M. Lynch, D. Rees, J. Galambos, D. Jeon,D. Raparia, J. Wei, R. Sundelin, K. Crandall, C. Pagani, P. Pierini, “Superconducting Linacfor the SNS~’ LA-UR-00-3938, International Linac Conference, Monterey, August, 2000 (tobe published).

M. Lynch, W. Reass, D. Rees, A. Regan, P. Tallerico, ‘The Spallation Neutron Source (SNS)Linac RF System: International Linac Conference, Monterey, August, 2000 (to bepublished). :.

.,~,.W. Reass, J. Doss, R. Gribble, M. Lynch, P. Tallerico, Progress on the 140,kV, 10-MegawattPeak, l-Megawatt Average, Polyphase Quasi-Resonant Bridge, Boost ConVerter/Modulatorfor the Spallation Neutron Source (SNS) Klystron Power System, International LinacConference, Monterey, August, 2000 (to be published).

A. Regan, S. Kwon, T. Rohley, Y. Wang, M. Prokop, D. Thomson, “Design of the SNSNormal Conducting Linac RF Control Systern~’ ]ritemational Linac Conference, Monterey,August, 2000 (to be published).

N. Pichoff, S. Nath, and J. M. Lagniel, Proceedkgs of the 1998 Lhac Conference, Chicago,Aug. 1998, 141.