SC-ECR ion source for RIKEN RIBF

1. IntroductionRequirements for RIKEN RIBF

2. Physics of ECR ion sourceEffects of the key components on the beamintensity and ECR plasma

3. RIKEN SC-ECRISSc-coils, plasma chamber, RF power supply

4. ResultsBeam intensity with 28GHz microwaveX-ray heat load

5. Future plan

T. NAKAGAWA (RIKEN)

RIKEN RIBF

Heavier than Xe ion

Lighter than Xe ion

~345MeV/u

18GHz ECR ion source

28GHZ SC-ECRIS

RILAC II

RILAC

RRC

FRCIRC

SRCBig RIPS(fragment separator)

18GHz ECRIS U ion beam ~60pnA(U35+ 2emA)

on target ~0.4pnA(345MeV/u)

>40 new isotopes were producedby in-flight fission reaction(4 days experiments)

New isotopes

T. Ohnishi et al, JPSL 79(2010)073201

Recent result at RIKEN RIBF I (new isotopes)

U35+(1010cm-3sec)

U20+(109 cm-3sec)

nq : ion densityV : plasma volumeti : ion confinement time

ne LargerV Largertc Shorterneti Constant (1010(cm-3ms)

(I)Plasma condition

(II)Beam intensity

QuestionHow to make these conditions ?

ne : electron densityti : ion confinement timeTopt: electron temperature

nq(cm-3) 1011 1012

ti(ms) 100 10I 1012 1014

U35+(1010cm-3sec)

Factor 100!

Production mechanism of intense beam of Highly Charged Heavy Ions

1)Magnetic field configurationplasma confinement & power absorption

2)Gas pressure3)Microwave frequency4)Plasma chamber size

ne : electron densityti : ion confinement timeTopt: electron temperature

Mechanism?

ne LargerV Largertc Shorterneti Constant (1010(cm-3ms)

Effect of the key components on the beam

Beam intensity

O5+ (14GHz)

Magnetic field configuration I (Bmin effect )

18GHz

14GHz~0.4T(0.8Becr)

~0.5T(0.8Becr)

N. I. M. A 491(2002)9 H. Arai et al,

3 solenoid coils magnetic mirror

Coil #1 Coil #2Coil #3

Sextupole CoilIronAluminum

Ex., “Flat Bmin “ structureG. D. Alton and D. N. Smithe,Rev. Sci. Instrum. 65 (1994) 775

3 solenoid coils Several solenoid coils (>3 coils)

SC-ECRISSuSI MSURIKEN28 RIKEN

Field gradient and surface size effect I

Field gradient

Energy transfer at ECR zone

Gentler field gradient

large energy transfer

Higher beam intensity

Larger zone size

Lager absorption

Higher beam intensity

Bext ~2Becr

Binj~3.5Becr

Magnetic field configuration II (Mirror ratio)

G. Ciavola et al, RSI 63(1992)2881

Gas pressure effect

Total beam current increases with increasing gas pressure

2x10-7Torr 7x10-7Torr~30pmA ~70pmA

Mean charge state decreases with increasing gas pressure

2x10-7Torr 7x10-7Torr<q>~3.5 ~2.2

Gas pressure effect

Electron density

Ion confinement time

(II)SECRAL(2009)

(I)SERSE (~2000)

Frequency effect I

SERSERF power1.8kW

Binj~3.5Becr,Bmin~0.8Becr,Bext~2BecrBr~2Becr

SECRAL

Binj~3.5Becr,Bmin~0.8Becr,Bext~2BecrBr~2Becr

H.W. Zhao et al, RSI 2010(81)02A202

S. Gammino et al, RSI 1999(70)3577

Y. Higurashi et al, accepted for publication to RSI

(III)RIKEN SC-ECRIS(2011)

Collision term HF term Source term

Strength of electric field(RF power)

Magnetic field gradient(Bmin effect)

m

BFokker-planck equation electron

Microwave Frequency effect II

A. Girard et al, J. Computational Phys.191(2003)228

Microwave Frequency effect III

Fokker planck equation

A. Girard et al, J. Computational Phys.191(2003)228

Absorption power

Total beam intensity

Optimization of magnetic field configuration

Gas pressure

Scenario to increase the beam intensity

Increase microwavefrequency

RF power

Bmin

BinjGas pressure

frequency

Chamber size effect (ion confinement time) I

Chamber size (quadrumafios)10times larger than caprice

q: charge stateL: chamber length

Ion confinement time

D. Hitz et al, Physica Scripta 1999

Physics background for designing of Sc-ECRIS

Magnetic field Binj ~4T Bext ~2T Br~2T (High B mode)(plasma confinement)Bmin <1T (~0.8Becr) (choose the optimum field gradient)ECR zone size as large as possible

Chamber size Diameter >15cm (comparison between RIKEN 18 GHzand VENUS, SCRAL)

Length >50cm (Long confinement time)

Microwave 28GHzPower >10kW ( 1kW/L)(High power density)

Binj ~3.8T Bmin <1.0T Bext ~2.3T

Br ~2.1T

For 28GHz operations

SC Solenoid coilsHexapole magnet

Microwave guide

Plasma chamber

Beam extraction system

Solenoid coil

Plasma chamber

Iron yoke

SC ECR ion source (RIKEN 28)

High energy Physics and Nuclear Physics 31(2007)37J. Ohnishi et al,

“Flat Bmin “ structureG. D. Alton and D. N. Smithe, Rev. Sci. Instrum. 65 (1994) 775

Main parameters of SC-Coils

High energy Physics and Nuclear Physics 31(2007)37J. Ohnishi et al,

Superconducting coils

Solenoid coils

Hexapole magnet

-400-200

0200400600800

10001200

-60 -40 -20 0 20 40 60Z (cm)

F (kN

/m)

Ft coil1Ft coil2Fr

-25cm 0 25cm

Strong force to hexapole magnet(~1100kNm max.)

Cryostat

(W)

Item Heliumvessel

Low temp.radiation

shield

High temp.radiation

shieldDesign temp. 4.2 K 20 K 70KRadiation 0.005 5.5 40Conduction

Support 0.005 0.3 4Port 0.06 1.5 20Current lead 0.07 10 64

Total heat load 0.14 17.3 128

GM refrig. 35W(45K), 6.3W(10K)

GM. Refrig. 50W(43K), 1.0W(4.2K)

CG310SC(SUMITOMO)(GM-JT refrig.)

Cooling capacity4.2W/5.0W@4.2K(50/60Hz)

Electric power consump. 5.1/6.1kW(50/60Hz)Electric power AC200V 3 phaseWeight ~220kgrDimension 700Wx520Dx1095H

SC Solenoid coilsHexapole magnet

Microwave guide

Movable biased disc

Beam extraction system

Solenoid coil Plasma chamber

Iron yoke

Plasma chamber

Plasma electrodeExtraction electrode (accel)

Extraction electrode (decel) Plasma chamber

SC Hexapole coil

Beam extraction system

RF injection side Beam extraction side

GM refrigerators

GM-JT refrigerator

Solenoid coilIron yoke

Picture (SC-ECRIS)

Analyzing magnet

Vacuum chamberECR ion source

beam

New injector system

U35+ beam productionSputtering method20~30emAlong term operation(> 1month)~100pmm mrad (~90%)

Gyrotron

Arc sensorMode converterTE02 TE01

Mode filter

High voltage break

Vacuum window

Plasma chamber

Conversion efficiency >95%TE02 TE01

RF 10kWmax

SC-ECRIS + Gyrotron

28GHz Gyrotron

Gyrotron

Xe ion production

Binj~3.2T, Bmin~0.63T, Bext~1.8TBr~1.85T

Binj~3.2T, Bext~1.8T,Br~1.85T

Plasma chamberExtraction electrode

Plasma electrode

Sc-solenoide coils

Biased disc

U rod

ECR zone

U-rod

Support rod(water cooled)

U ion beam production

Sputtering method

Injected power (plasma chamber) vs. U35+ beam

Output power (Gyrotron)vs. U35+ beam

Binj~3.2T, Bmin~0.63T, Bext~1.8TBr~1.85T

Bo : axial magnetic fieldq: charge stateM: mass

Bo 18GHz ~1.2T28GHz ~1.8T

Cal: same q/M same emittance

: higher Bo larger emittance

Emittance measurements

VENUS 28GHz

RIKEN SC-ECRIS 28GHz

X-ray heat load

High energy x-ray (>several 100keV)

plasmacryostat

D. Leitner et al, RSI 79(79)033302

Y. Higurashi et al, accepted for publication to RSI

X-ray heat load (field gradient effect) I

Gentler field gradient

Higher beam intensity

Cooling power is limited by cryo-cooler(several W)

Increase the cooling power

Minimizing the heat load while keeping or increasing the beam intensity

X-ray heat load (field gradient effect) III

D. Leitner et al, RSI 79(2008)02C710

RF power >6kW U35+~200emA

using High temp. Ovenmore U vapour

Next step – increase of U beam-

Next step-RIKEN SC-ECRIS

1. Optimizing the magnetic field distribution for 28GHz

2. Use of Al chamber ( cold electron doner)

3. Increase the RF power (>6kW)

4. Stabilizing the beam intensity

5. Optimizing the extraction