1. MA CAVITIES Chihiro Ohmori (KEK) 2009/7/1PRISM Workshop@Imperial College1

2. contents Ferrite loaded cavity MA cavity – MA = Magnetic Alloy Characteristics of MA Six types of MA cavities – Cooling – Q-value Design issues Summary 2009/7/1PRISM Workshop@Imperial College2

3. Ferrite cavities In hadron accelerators, velocity of particle changes (not  =1 as electron accelerators). When synchrotron was developed ferrite cavity was the most possible scheme to sweep the rf frequency. 2009/7/1PRISM Workshop@Imperial College3 Beam pipe Ferrite ring

4. Ferrite Cavity 2009/7/1PRISM Workshop@Imperial College4 As ferrite cavity (resonant circuit) has large Q-value (=narrow band), need to sweep the resonant frequency applying a bias current.

5. Ferrite cavity HIMAC Ferrite Cavity & AMP Courtesy of M. Kanazawa 2009/7/1PRISM Workshop@Imperial College5

6. Ferrite Cavity Pro. – Established technique, long history Con. – Limited field gradient because of core saturation, long cavity length – Biasing circuit, cavity tuning, long cavity for large rf sweep. – Other RF station for the 2 nd harmonic RF to increase the beam intensity 2009/7/1PRISM Workshop@Imperial College6

7. MA cavity for Synchrotron Ring core made of Magnetic alloy ribbons. Cavity use starts in 1995. For Cavity use, put SiO 2 insulation of 2  m. Annealing (amorphous, Metglas) or Nano crystallization (Finemet) or Annealing in Magnetic Field (Co amorphous) 2009/7/1PRISM Workshop@Imperial College7

8. Characteristics of Magnetic Cores 200V/div, 5ms/div High Loss Effect Magnetic Alloys Ferrites 2000 Gauss 2009/7/1PRISM Workshop@Imperial College8 ∝ rf voltage ∝ shunt impedance

9. Comparison MAFerrite (Ni-Zn) Saturation flux density 1.2 T0.4 T Possible Acc. Field gradient High (25kV/m for J-PARC) (depend on duty factor) Below ~15kV/m (depend on freq. and I.D.) Permeability~3000~500 Core impedance Few 100  /coreFew 100  /core depend on voltage Q-value~0.6Few 100 BandwidthWideNarrow 2009/7/1PRISM Workshop@Imperial College9

10. Impact on RCS design by High Field Gradient Left: J-PARC RCS has about 350 m circumference. Black line means the space for RF (44 m, including Q- magnets). Middle: 3 GeV Ring using ferrite cavity. Red line means additional space by low gradient. Blue is by the extended circumference. Right: 3 GeV ring using ferrite cavity with 2 nd H system (orange). 2009/7/1PRISM Workshop@Imperial College10 Ferrite cavity 2 nd Harmonics

11. MA CAVITIES 2009/7/1PRISM Workshop@Imperial College11

12. Classification Un-cut coreCut core Air cooling AGS barrier cavity, KEK-PSB cavities, HIMAC chopper, Heidelberg cavity, Tsukuba cavity, Wakasa cavity RIKEN chopper Indirect cooling MIMAS cavity, HIMAC 2 nd MA cavity, GUNMA cavity( in R&D) J-PARC R&D cavity FNAL bunch manipulation cavity? Direct water cooling HIMAC MA cavity, J-PARC RCS cavities, COSY cavity, CERN LEIR cavities J-PARC MR cavities 2009/7/1PRISM Workshop@Imperial College12

13. UnCut / Cut Core MA has a large permeability and wide bandwidth. But, sometimes, narrow bandwidth and high resonant frequency are preferable. High Q (~26) cores are used for J-PARC MR cavity. 2009/7/1PRISM Workshop@Imperial College13

14. Cooling Scheme MA cavity can generate high field gradient. However, the heat dissipation should be removed by proper way. Three cooling schemes – Air cooling : AGS H=1,2 cavity (barrier cavity), KEK PS booster MA cavity Low duty or low voltage – Indirect cooling : MIMAS cavity, HIMAC 2 nd MA cavity, 150 MeV FFAG cavity – Direct water cooling : J-PARC, CERN-LEIR, HIMAC MA cavity High duty or in case of less space 2009/7/1PRISM Workshop@Imperial College14

15. Air cooled Uncut core cavity AGS barrier bucket cavity (1998-) M. Fujieda et al., “Barrier Bucket Experiment at the AGS”Phys. Rev. STAB 2 122001(1999) Still using as bunch manipulation cavity for RHIC 2009/7/1PRISM Workshop@Imperial College15

16. Air cooled Uncut core cavity KEK-PS booster cavity 2.2-6.1 MHz 16 kV 2 X 0.525 m Non-resonant Accelerating System at the KEK-PS Booster, S. Ninomiya et al., Proceedings of EPAC2004, Lucerne, Switzerland, p1027 2009/7/1PRISM Workshop@Imperial College16

17. Air Cooled Uncut core cavity Heidelberg Ion beam Therapy 1~7 MHz 2.5 kV 1.4 m Made by HITACHI Development of RF Acceleration System for Ion therapy Synchrotron, Takamitsu Hae et al., Proceedings of the 2nd Annual Meeting of Particle Accelerator Society of Japan and the 30th Linear Accelerator Meeting in Japan July 20-22, 2005, Tosu Japan, p543 (in Japanese). 2009/7/1PRISM Workshop@Imperial College17

18. Air cooled Cut core cavity (chopper) RIKEN buncher for Ring Cyclotron 18-45 MHz (narrow band) 0.1 kV 0.12 m Development of Buncher cavity using MA cores, T. Koseki et al., Proceedings of the 2nd Annual Meeting of Particle Accelerator Society of Japan and the 30th Linear Accelerator Meeting in Japan, July 20-22, 2005, Tosu Japan, 329 (in Japanese). 2009/7/1PRISM Workshop@Imperial College18

19. Indirect Cooled Uncut core cavity Probably, this is the first MA cavity. Courtesy of A. Schnase 2009/7/1PRISM Workshop@Imperial College19

20. Indirect cooled Uncut core cavity 2 nd HIMAC MA cavity Acceleration cavity New : 1.5m present Beam test at HIMAC RF cavity with Co- based amorphous core, M. Kanazawa et al., Proc. of EPAC2004, p983. Made by Toshiba 2009/7/1PRISM Workshop@Imperial College20

21. High power test （４＊２ｋＷ） Temperature of core surface RF voltage Courtesty of M. Kanazawa (NIRS) 2009/7/1PRISM Workshop@Imperial College21

22. Indirect cooled Cut core cavity J-PARC R&D cavity Problems – Cooling was not enough. – Bad contact between core and cooling plate. C. Ohmori et al., “High Field Gradient Cavity for JAERI-KEK Joint Project”, EPAC2002. 2009/7/1PRISM Workshop@Imperial College22

23. Indirect cooled Cut core cavity FNAL MA cavity For beam manipulation Courtesy of Wildman(FNAL) 2009/7/1PRISM Workshop@Imperial College23

24. C. Ohmori et al., “A multi-harmonic RF System using a MA cavity, NIM A 547,p249-258. Direct water cooled Uncut core cavity HIMAC MA cavity 1-8 MHz 4 kV at 1-3 MHz 2009/7/1PRISM Workshop@Imperial College24

25. Direct water cooled Uncut core cavity COSY cavity A. Schnase et al., “Experience with a broadband VITROPERM-filled cavity at the synchrotron COSY”, EPAC2002. 2009/7/1PRISM Workshop@Imperial College25

26. Direct water cooled Uncut core cavity CERN LEIR Cavities 0.35-5 MHz 4 kV 0.4 m R. Garoby et al.,”the LEIR RF System”, PAC05 2009/7/1PRISM Workshop@Imperial College26

27. LEIR RF SYSTEM – RING SECTION Free space is used for H=2 RF system, now. 2009/7/1PRISM Workshop@Imperial College27

28. Magnetic Alloy cores （ water-proof coating ） 2009/7/1PRISM Workshop@Imperial College28

29. Direct Water cooling Uncut core cavity J-PARC RCS cavities 0.94-1.67 MHz 40-45 kV (36 kV for operation) 2 m 11 cavities in RCS Dual Harmonic operation for high intensity Increase Q-value by external inductor 2009/7/1PRISM Workshop@Imperial College29

30. J-PARC We succeeded to accelerate the beam to 3 GeV (2PM, Oct. 31st), 30 GeV on last Dec. 2009/7/1PRISM Workshop@Imperial College30 Down time was very little while beam operation. But, some of 198 cores shows degradation by buckling.

31. 11 RF system for RCS 2009/7/1PRISM Workshop@Imperial College31

32. 2009/7/1PRISM Workshop@Imperial College32

33. Single harmonicsDual harmonics RCS beam 2009/7/1PRISM Workshop@Imperial College33

34. Direct Water Cooling Cut Core Cavity J-PARC MR cavity 1.67-1.7MHz 1.8 m 45 kV (40 kV for operation) 5 RF systems (Summer 2009) Q=26 to manage high intensity beam – To stand heavy beam loading 2009/7/1PRISM Workshop@Imperial College34

35. 2009/7/1PRISM Workshop@Imperial College35

36. 2009/7/1PRISM Workshop@Imperial College36

37. J-PARC RF Cavities -Stability for heavy beam loading -Wideband and no tuning -High Field Gradient using Magnetic Alloy -First time to use many MA cavities - Multi- Harmonic RF Cavities for RCS 2009/7/1PRISM Workshop@Imperial College37

38. FFAG cavities Air coolingPoP FFAG PRISM FFAG Indirect water cooling150 MeV FFAG InductionIon beta FFAG Normalconducting RFEMMA (non-scaling FFAG in UK) 2009/7/1PRISM Workshop@Imperial College38

39. Air-cooled uncut core cavity PoP FFAG cavity 2009/7/1PRISM Workshop@Imperial College39

40. Cavity assembly 150 MeV FFAG Number of cores2~4 Outer size1.7m x 1m Inner size1m x 0.23m RF frequency1.5 - 4.6 MHz RF voltage9 kV RF output55 kW Power density1 W/cm^3 Cooling water70 L/min Indirect cooling 2009/7/1PRISM Workshop@Imperial College40

41. Air cooling 2009/7/1PRISM Workshop@Imperial College41

42. DESIGN OF MA CAVITY SYSTEM 2009/7/1PRISM Workshop@Imperial College42

43. RF System MA Cavity MA cavity – Passive LCR circuit Final stage AMP – Wideband circuit, multi-H – CG: all pass network Driver AMP – Few kW Low Level RF – Multi-H – ALC, (phase, orbit), beam loading Ferrite loaded cavity Ferrite Cavity – Bias PS for tuning cavity Final stage AMP – Narrow band Driver AMP – About 1 kW Low Level RF – Single H – ALC, phase, orbit, tuning loop, beam loading 2009/7/1PRISM Workshop@Imperial College43

44. CAVITY DESIGN for wideband system LEIR RF SYSTEM Cavity Model: Half Cavity Z (1 Core ) Low Frequency response <<20dB/dec 2009/7/1PRISM Workshop@Imperial College44

45. LEIR RF SYSTEM Cavity Model: Half Cavity Z (1 Core ) Additional C : 0 +20pF +40pF +100pF Response similar to that of an RC circuit. Above cutoff the slope is mainly dependent on C value. Structure capacitance is ~12pF. M. Paoluzzi 2009/7/1PRISM Workshop@Imperial College45

46. Capacitance from AMP 2009/7/1PRISM Workshop@Imperial College46

47. Control of Q-value w/o cutting Parallel inductance reduces inductance of resonant circuit. Additional capacitor Preferable Q-value for RCS, 2, for BL and dual H. It is too high for uncut core and too low for cut core. CAVITY DESIGN for High intensity 2009/7/1PRISM Workshop@Imperial College47

48. Cut Core cavity Cut core cavity is used for – Accelerator with transient beam loading + very short beam …………J-PARC MR – Accelerator with high resonant frequency and narrow band ……….RIKEN beam chopper High voltage and high power use requires a good cutting scheme to avoid destruction of ribbon insulation. Destruction of insulation of 2  m will cause local heating of cut surface. CAVITY DESIGN for High intensity 2009/7/1PRISM Workshop@Imperial College48

49. Cut Core Configuration 2009/7/1PRISM Workshop@Imperial College49

50. Q-value of MA cavity CoreQFrequencyUsesAccelerators Uncut core~0.6300kHz-3MHzLow energy, Ion synchrotron, Bunch manipulation KEK PS booster, CERN LEIR, Medical use, AGS (Barrier bucket, Bunch Stacking) Hybrid2-Few MHz -Medium energy High intensity w/o transient B.L. J-PARC RCS Cut core5-Few MHz-(few 10MHz) High energy High intensity with transient B.L., High frequency use J-PARC MR, Riken beam Chopper 2009/7/1PRISM Workshop@Imperial College50

51. Cooling Scheme AirLow duty<0.2 W/ccAGS barrier Medical use Simple Forced AirHigh duty? 0.5 W/ccKEK PS booster IndirectHigh duty< 0.5 W/ccJHF R&D Medical use Direct- water High duty1 W/ccWaterJ-PARC MR, RCS High power use Direct- other Low duty?Florinate Silicon oil KEK PS 2 nd KEK PS induction Good for higher freqeuncy 2009/7/1PRISM Workshop@Imperial College51

52. Materials MaterialsImpedanceuseRibbon Insulation Maker Fe- amorphousLowMIMASAllied, Hitachi-Metal Co- amorphousHighGunma MedicalAllied, Toshiba Nano- crystalneHighJ-PARC, AGS, CERN, Riken SiO2 2  m Hitachi-Metal New MAHigher SiO2 2  m FerriteHigh at low voltage Many 2009/7/1PRISM Workshop@Imperial College52

53. Summary MA based RF systems for synchrotron and FFAG are reviewed. 2009/7/1PRISM Workshop@Imperial College53