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  1. MA CAVITIES Chihiro Ohmori (KEK) PRISM Workshop@Imperial College

  2. contents • Ferrite loaded cavity • MA cavity • MA = Magnetic Alloy • Characteristics of MA • Six types of MA cavities • Cooling • Q-value • Design issues • Summary PRISM Workshop@Imperial College

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

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

  5. Ferrite cavity HIMAC Ferrite Cavity & AMP Courtesy of M. Kanazawa PRISM Workshop@Imperial College

  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 2nd harmonic RF to increase the beam intensity PRISM Workshop@Imperial College

  7. MA cavity for Synchrotron • Ring core made of Magnetic alloy ribbons. • Cavity use starts in 1995. Annealing (amorphous, Metglas) or Nano crystallization (Finemet) or Annealing in Magnetic Field (Co amorphous) For Cavity use, put SiO2 insulation of 2 mm. PRISM Workshop@Imperial College

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

  9. Comparison PRISM Workshop@Imperial College

  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 2nd H system (orange). Ferrite cavity 2nd Harmonics Ferrite cavity PRISM Workshop@Imperial College

  11. MA cavities PRISM Workshop@Imperial College

  12. Classification PRISM Workshop@Imperial College

  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. PRISM Workshop@Imperial College

  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 2nd MA cavity, 150 MeV FFAG cavity • Direct water cooling : J-PARC, CERN-LEIR, HIMAC MA cavity • High duty or in case of less space PRISM Workshop@Imperial College

  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 PRISM Workshop@Imperial College

  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 PRISM Workshop@Imperial College

  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 JapanJuly 20-22, 2005, Tosu Japan , p543 (in Japanese). PRISM Workshop@Imperial College

  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). PRISM Workshop@Imperial College

  19. Indirect Cooled Uncut core cavity • Probably, this is the first MA cavity. Courtesy of A. Schnase PRISM Workshop@Imperial College

  20. Indirect cooled Uncut core cavity2nd HIMAC MA cavity Acceleration cavity present Beam test at HIMAC New : 1.5m RF cavity with Co-based amorphous core, M. Kanazawa et al., Proc. of EPAC2004, p983. Made by Toshiba PRISM Workshop@Imperial College

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

  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. PRISM Workshop@Imperial College

  23. Indirect cooled Cut core cavity • FNAL MA cavity • For beam manipulation Courtesy of Wildman(FNAL) PRISM Workshop@Imperial College

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

  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. PRISM Workshop@Imperial College

  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 PRISM Workshop@Imperial College

  27. LEIR RFSYSTEM – RING SECTION Free space is used for H=2 RF system, now. PRISM Workshop@Imperial College

  28. Magnetic Alloy cores (water-proof coating) PRISM Workshop@Imperial College

  29. Direct Water cooling Uncut core cavityJ-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 PRISM Workshop@Imperial College

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

  31. 11 RF system for RCS PRISM Workshop@Imperial College

  32. PRISM Workshop@Imperial College

  33. RCS beam Single harmonics Dual harmonics PRISM Workshop@Imperial College

  34. Direct Water Cooling Cut Core CavityJ-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 PRISM Workshop@Imperial College

  35. PRISM Workshop@Imperial College

  36. PRISM Workshop@Imperial College

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

  38. FFAG cavities PRISM Workshop@Imperial College

  39. Air-cooled uncut core cavity PoP FFAG cavity PRISM Workshop@Imperial College

  40. Indirect cooling Cavity assembly150 MeV FFAG • Number of cores 2~4 • Outer size 1.7m x 1m • Inner size 1m x 0.23m • RF frequency 1.5 - 4.6 MHz • RF voltage 9 kV • RF output 55 kW • Power density 1 W/cm^3 • Cooling water 70 L/min PRISM Workshop@Imperial College

  41. Air cooling PRISM Workshop@Imperial College

  42. Design of Ma cavity system PRISM Workshop@Imperial College

  43. RF System MA Cavity 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 • 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 PRISM Workshop@Imperial College

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

  45. LEIR RF SYSTEMCavity 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 PRISM Workshop@Imperial College

  46. Capacitance from AMP PRISM Workshop@Imperial College

  47. CAVITY DESIGN for High intensity 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. PRISM Workshop@Imperial College

  48. Cut Core cavity CAVITY DESIGN for High intensity • 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 2mm will cause local heating of cut surface. PRISM Workshop@Imperial College

  49. Cut Core Configuration PRISM Workshop@Imperial College

  50. Q-value of MA cavity PRISM Workshop@Imperial College