SC-ECR ion source for RIKEN RIBF

Transcription

1 SC-ECR ion source for RIKEN RIBF T. NAKAGAWA (RIKEN) 1. Introduction Requirements for RIKEN RIBF 2. Physics of ECR ion source Effects of the key components on the beam intensity and ECR plasma 3. RIKEN SC-ECRIS Sc-coils, plasma chamber, RF power supply 4. Results Beam intensity with 28GHz microwave X-ray heat load 5. Future plan

2 RIKEN RIBF Heavier than Xe ion ~345MeV/u 18GHz ECR ion source Lighter than Xe ion RILAC 28GHZ SC-ECRIS RRC RILAC II FRC IRC SRC Big RIPS (fragment separator)

3 Recent result at RIKEN RIBF I (new isotopes) New isotopes 18GHz ECRIS U ion beam ~60pnA(U 35+ 2emA) on target ~0.4pnA(345MeV/u) >40 new isotopes were produced by in-flight fission reaction (4 days experiments) T. Ohnishi et al, JPSL 79(2010)073201

4 (I)Plasma condition Production mechanism of intense beam of Highly Charged Heavy Ions (II)Beam intensity U 35+ (10 10 cm -3 sec) U 20+ (10 9 cm -3 sec) n e : electron density t i : ion confinement time T opt : electron temperature n e V t c n e t i Larger Larger Shorter Constant (10 10 (cm -3 ms) U 35+ (10 10 cm -3 sec) n q (cm -3 ) t i (ms) I Factor 100! n q : ion density V : plasma volume t i : ion confinement time Question How to make these conditions?

5 Effect of the key components on the beam 1)Magnetic field configuration plasma confinement & power absorption 2)Gas pressure 3)Microwave frequency 4)Plasma chamber size Mechanism? Beam intensity n e V t c n e t i Larger Larger Shorter Constant (10 10 (cm -3 ms) n e : electron density t i : ion confinement time T opt : electron temperature

6 Magnetic field configuration I (B min effect ) O 5+ (14GHz) 3 solenoid coils magnetic mirror ~0.5T(0.8B ecr ) 18GHz N. I. M. A 491(2002)9 H. Arai et al, ~0.4T(0.8B ecr ) 14GHz

7 3 solenoid coils Several solenoid coils (>3 coils) Coil #1 Coil #3 Coil #2 Aluminum Iron Sextupole Coil Ex., Flat B min structure G. D. Alton and D. N. Smithe, Rev. Sci. Instrum. 65 (1994) 775 SC-ECRIS SuSI MSU RIKEN28 RIKEN

8 Field gradient and surface size effect I Energy transfer at ECR zone Field gradient Gentler field gradient large energy transfer Larger zone size Lager absorption Higher beam intensity Higher beam intensity

9 Magnetic field configuration II (Mirror ratio) B ext ~2B ecr B inj ~3.5B ecr G. Ciavola et al, RSI 63(1992)2881

10 Gas pressure effect Total beam current increases with increasing gas pressure 2x10-7 Torr ~30pmA 7x10-7 Torr ~70pmA Mean charge state decreases with increasing gas pressure 2x10-7 Torr 7x10-7 Torr <q>~3.5 ~2.2

11 Gas pressure effect Electron density Ion confinement time

12 Frequency effect I (I)SERSE (~2000) SERSE RF power1.8kw B inj ~3.5B ecr, B min ~0.8B ecr, B ext ~2B ecr B r ~2B ecr (III)RIKEN SC-ECRIS(2011) S. Gammino et al, RSI 1999(70)3577 (II)SECRAL(2009) SECRAL B inj ~3.5B ecr, B min ~0.8B ecr, B ext ~2B ecr B r ~2B ecr H.W. Zhao et al, RSI 2010(81)02A202 Y. Higurashi et al, accepted for publication to RSI

13 Microwave Frequency effect II Fokker-planck equation B electron Collision term HF term Source term m Strength of electric field (RF power) Magnetic field gradient (B min effect) A. Girard et al, J. Computational Phys. 191(2003)228

14 Fokker planck equation Microwave Frequency effect III Absorption power A. Girard et al, J. Computational Phys. 191(2003)228 Total beam intensity

15 frequency Scenario to increase the beam intensity Gas pressure RF power B min Optimization of magnetic field configuration B inj Gas pressure Increase microwave frequency

16 Chamber size effect (ion confinement time) I Ion confinement time Chamber size (quadrumafios) 10times larger than caprice q: charge state L: chamber length D. Hitz et al, Physica Scripta 1999

17 Physics background for designing of Sc-ECRIS Magnetic field B inj ~4T B ext ~2T B r ~2T (High B mode)(plasma confinement) B min <1T (~0.8B ecr ) (choose the optimum field gradient) ECR zone size as large as possible Chamber size Microwave Diameter >15cm (comparison between RIKEN 18 GHz and VENUS, SCRAL) Length >50cm (Long confinement time) 28GHz Power >10kW ( 1kW/L)(High power density)

18 SC ECR ion source (RIKEN 28) Beam extraction system SC Solenoid coils Hexapole magnet Microwave guide Solenoid coil Iron yoke Plasma chamber For 28GHz operations B inj ~3.8T B min <1.0T B ext ~2.3T High energy Physics and Nuclear Physics 31(2007)37 J. Ohnishi et al, Plasma chamber B r ~2.1T Flat B min structure G. D. Alton and D. N. Smithe, Rev. Sci. Instrum. 65 (1994) 775

19 High energy Physics and Nuclear Physics 31(2007)37 J. Ohnishi et al, Main parameters of SC-Coils

20 Superconducting coils Solenoid coils Hexapole magnet

21 -25cm 0 25cm Strong force to hexapole magnet (~1100kNm max.) Ft coil1 Ft coil2 Fr Z (cm)

22 Cryostat CG310SC(SUMITOMO)(GM-JT refrig.) Cooling capacity Electric power consump. 5.1/6.1kW(50/60Hz) Electric power AC200V 3 phase Weight ~220kgr Dimension 700Wx520Dx1095H GM refrig. 35W(45K), 6.3W(10K) GM. Refrig. 50W(43K), 1.0W(4.2K) Item Helium vessel Low temp. radiation shield (W) High temp. radiation shield Design temp. 4.2 K 20 K 70K Radiation Conduction Support Port Current lead Total heat load

23 Plasma chamber Beam extraction system Hexapole magnet SC Solenoid coils Microwave guide Solenoid coil Plasma chamber Movable biased disc Iron yoke

24 Beam extraction system Extraction electrode (accel) Plasma electrode Extraction electrode (decel) Plasma chamber SC Hexapole coil

25 Picture (SC-ECRIS) GM-JT refrigerator GM refrigerators RF injection side Beam extraction side Iron yoke Solenoid coil

26 Vacuum chamber ECR ion source beam Analyzing magnet

27 U 35+ beam production Sputtering method 20~30emA long term operation(> 1month) ~100pmm mrad (~90%) New injector system

28 SC-ECRIS + Gyrotron Mode filter Plasma chamber High voltage break Vacuum window Conversion efficiency >95% TE02 TE01 Mode converter TE02 TE01 Arc sensor RF 10kWmax Gyrotron

29 28GHz Gyrotron Gyrotron

30 Xe ion production B inj ~3.2T, B ext ~1.8T,B r ~1.85T B inj ~3.2T, B min ~0.63T, B ext ~1.8T B r ~1.85T

31 U ion beam production Plasma chamber ECR zone Plasma electrode Extraction electrode Sputtering method U-rod Biased disc U rod Sc-solenoide coils Support rod(water cooled)

32 Output power (Gyrotron)vs. U 35+ beam Injected power (plasma chamber) vs. U 35+ beam B inj ~3.2T, B min ~0.63T, B ext ~1.8T B r ~1.85T

33 Emittance measurements Bo : axial magnetic field q: charge state M: mass Cal: same q/m same emittance : higher Bo larger emittance Bo 18GHz ~1.2T 28GHz ~1.8T

34 X-ray heat load High energy x-ray (>several 100keV) VENUS 28GHz D. Leitner et al, RSI 79(79) cryostat plasma RIKEN SC-ECRIS 28GHz Y. Higurashi et al, accepted for publication to RSI

35 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

36 X-ray heat load (field gradient effect) III

37 Next step increase of U beam- RF power >6kW U 35+ ~200emA using High temp. Oven more U vapour D. Leitner et al, RSI 79(2008)02C710

38 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