Lecture #3

Atomic Physics with Stored andCooled Ions

Klaus BlaumGesellschaft für Schwerionenforschung, GSI, Darmstadt

and CERN, Physics Department, Geneva, Switzerland

Summer School, Lanzhou, China, 9 – 17 August 2004

3. Lecture: Production of radioactive nuclei

and highly-charged ions 1. Production techniques for radioactive ion beams (RIB)2. The heavy ion accelerator facility GSI3. The on-line isotope separator ISOLDE at CERN4. Production of highly-charged ions (HCI)

- at GSI- with an Electron Beam Ion Trap (EBIT)

Ion traps, heavy ion cooler rings andlaser traps at accelerators

Stockholm • • Aarhus

• Tokyo

• CERN • GSI Heidelberg

Argonne• • Berkeley

• Jyväskylä

• Stony Brook • Vancouver

•MSU k • Lanzhou

plans at GANIL, KVI Groningen, Leuven, Penning trap for neutron lifetime at ILL, Grenobleoff-line experiments at Los Alamos

Radioactive ion beam production: principle

ε = f ( )Transmission, element, half-life, ionization, ...

0.1 / day - > 1012 / s

ion beam preparation, separation, acceleration/deceleration, ...

PrinciplePrimary beam Secondary beamnuclear

reactionI0 IRIB

Reaction rateCross sections 1 pb – > 10 b Beam flux 1011 – 1015 /cm2 /sTarget thickness 0.1 – 100 g/cm2

R = σreaction · φprimary · Ntarget

RIB intensity

IRIB = ε · R

Proton-induced reactions (e.g. ISOLDE, ISAC)

protons

pn

+ Spallation

+ + Fragmentation

+ + Fission

201Fr

11Li X

143Cs Y

238U1 GeV

Heavy-ion-induced reactions (e.g. GSI)

Fragmentation

Coulomb dissociation

Fusion

ISOL versus fragmentation

FragmentationISOL

accelerator1 GeV protons,Light ions

1 GeV/u heavy ions

productiontargetthick thin

ion source

100 keV 1 GeV/u

electromagneticseparationhigh intensities for

long-lived isotopeslimitation at T1/2 < 10 ms

high beam qualityno refaractory elements

low intensities

limitation only at T1/2 < 1µs

low beam qualityall elements

postaccelerator

decellerator

some MeV At rest

ISOL and fragmentation facilities are complementary

Concept for in-flight separation

Primary beam heavy ions

Target thin

Separation gas-filledseparators

B<q>=Z1/3 v/vBohr

velocityFilters

E x B

fragment separators

BBρ = mv /qEρ = mv2/q

Experiment

B: magnetic field E: electric sector fieldρ: deflection radius m: massv: velocity q: charge stateZ: atomic number

Concept for ISOL

ions p, d, n Primary beam

Target thin thick

Catcher

Ion Source

Extraction +Separation

solidgas

various

Manipulation and cooling of RIB and HCI

good beam qualityhigh intensity

MS

MS

Target

ionsource

heavy ions, <2GeV/u

protons, 1 GeV

beam coolinglow emittance, energy spread

accumulation and bunchingsignal-to-noise ratio, beam transfer, beam energy variation

beam purificationclean ion beams

Improvements via:

Demands:

The heavy ion accelerator GSI

Mission:Construction and operation

of accelerators; research with heavy ions

Personnel:ca. 700 employees

(250 scientists and engineers)

Instruments:Accelerators

UNILAC/SIS/ESR;large spectrometersand detector systems

Altogether over 1000 users, 400 from abroad

(100 internal users)Budget:65 Mio €

Operation: 52 Mio €Investments: 13 Mio €

http://www.gsi.de

Research programm at GSI

Atomic Physics

15%

Plasma Physics

5%

AstrophysicsCosmology

Nuclear Physics

50%

AcceleratorDevelopment

10%

Materials Research

5%

Biophysics &Tumortherapy

15%

New Technologies

New Materials

Clinical Application

Joint effort of GSI & university groups and international collaboration

Ion (stopping and) collection devices at GSI

Existing Collection Devices

SISESR

+ STOPPINGSHIPTRAP

Planned DevicesHITRAP

FRS gas cell

The ISOLDE facility at CERN

Control room

HV-Platform

RILIS laser hut

Robots

Radioactive laboratory

1.4 GeV protonsfrom PS-Booster

HRS-Target

GPS-Target

COLLAPS

ISOLTRAP

http://isolde.web.cern.ch/isolde

E. Kugler, Hyp. Int. 129, 23-42 (2000).

ISOLDE Target

Protons

8 V500 A

9 V1000 A

E. Kugler, Hyp. Int. 129, 23-42 (2000).

Ionization techniques:• Surface ionization• Plasma ionization• Resonant laser ionization

before after http://isolde.web.cern.ch/isolde

Resonance Ionization Laser Ion Source (RILIS)

1. Surface Ionization Ion Source:No isobaric selectivity, limited applicability

2. Plasma Ion Source (ECR-Source):No isobaric selectivity

3. Resonance Ionization Laser Ion Source (RILIS):High isobaric selectivity by resonant laser ionizationLimitation by surface ionized isobars

U. Köster, V. Fedoseyev et al.,

Spectrochim Acta 58B, 1047 (2003)

Accessibility of elements by RILIS

1H 2He

3Li 4Be 5B 6C 7N 8O 9F 10Ne

11Na 12Mg 13Al 14SI 15P 16S 17Cl 18Ar

19K 20Ca 21Sc 22Ti 23V 24Cr 25Mn 26Fe 27Co 28Ni 29Cu 30Zn 31Ga 32Ge 33As 34Se 35Br 36Kr

37Rb 38Sr 39Y 40Zr 41Nb 42Mo 43Tc 44Ru 45Rh 46Pd 47Ag 48Cd 49In 50Sn 51Sb 52Te 53I 54Xe

55Cs 56Ba 57La 72Hf 73Ta 74W 75Re 76Os 77Ir 78Pt 79Au 80Hg 81Tl 82Pb 83Bi 84Po 85At 86Rn

87Fr 88Ra 89Ac 104Rf 105Ha 106 107 108 109 110 111 112 113

58Ce 95Pr 60Nd 61Pm 62Sm 63Eu 64Gd 65Tb 66Dy 67Ho 68Er 69Tm 70Yb 71Lu

90Th 91Pa 92U 93Np 94Pu 95Am 96Cm 97Bk 98Fc 99Es 100Fm 101Md 102No 103Lr

Elements studied with dye – laser RIS Dye - laser RIS possible

Ti:Sa laser RIS demonstrated Ti:Sa laser RIS possible

U. Köster, V. Fedoseyev et al.,

Spectrochim Acta 58B, 1047 (2003)

K. W. et al, Proceedings RnB 6, ANL,USA

Nucl. Instr. Meth. in Phys. Res., in press

At ISOLDE in total >70 elements, >600 isotopes available!

Physics at ISOLDE

Nuclear Physics49%

Nuclear Decay Spectroscopy and Reactions

Structure of NucleiExotic Decay Modes

Atomic Physics18%

Laser Spectroscopy and Direct Mass Measurements

Radii, Moments, Nuclear Binding Energies

Nuclear Astrophysics

14%Dedicated Nuclear

Decay/Reaction StudiesElement Synthesis,

Solar Processes

f ( N, Z )

Fundamental Physics

Direct Mass Measurements, Dedicated Decay Studies – WI

CKM unitarity tests, search for β-ν correlations, right-handed

currents

Applied Physics19%

Implanted Radioactive Probes, Tailored Isotopes for Diagnosis

and Therapy

Condensed matter physics and Life sciences

Ion stopping and collection devices at ISOLDE

Existing DevicesREXTRAP

WITCH Penning trapsISOLTRAP RFQ buncher

ISOLTRAP cooler trap

Planned DevicesISOLDE HRS cooler

MISTRAL cooler

Production of highly-charged ions at GSI

HCI production in an EBIT

axial potential

radial potential

topdrift tube

centerdrift tube

bottondrift tube

electron beam

trapped ions

LN

LHe

SC magnetcoils

electron gun

collector

drift tubes

window

EBIT II

The electron beam ion trap (EBIT) was developed at theLawrence Livermore National Laboratory (LLNL) in the late1980s by R. Marrs and M. Levine

2

The ionization process

Sequential electron impact ionization in an electron beam ion trap

As the ion charge state goes up:• growing ionization potential:

10 eV → 130000 eV• diminishing cross section:

10-16 cm2 → 10-24 cm2

130 keV

31 keV12 keV

n=1

n=2 n=3

electron beam with energy Ek

continuum

Competing processes: recombination

charge exchange with restgas neutral atomsN

n n

n

nn

n n

n

nn

Ne9+

solution: vacuum 10-13 Torr

(1000 atoms/cm3)

capture of free electrons

n n

n

nn

γ radiative recombination (RR)

solution: raising electron beam energy

Be--beam

60 µ

m

40 mm

trap potential Ut ≈ 100 V(Ut × ion charge) ≈ 5000 eV

6000 A/cm2

ne ≈ 1013 e-/cm3

longitudinally:electrodes

Principles of an EBIT (electron beam ion trap)

the trap:

axially:electron beam space charge

Evaporative cooling

• collisions with beam electrons heat up ion ensemble• light, less tightly trapped ions (e.g. Ne10+ ) evaporate removingthermal energy: a single Ne10+ takes away 2 keV (1 second additional life for a heavy ion)

• heavy, highly charged ions (e.g. Ba53+ ) remain trapped indefinitely

Ion temperatures from 1000 eV to 10 eV

Doppler width ∆λ/λ ≈ 1/20.000 (Ba53+)

High resolution spectroscopy