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PRISM RF

PRISM RF. C. Ohmori 　（ KEK). Contents. PRISM RF Introductions Present status, RF for a beam RF for 6 cell ring Upgrade plan EMMA RF RF system for PRSIM. Requirements for RF. High voltage at 3.8 MHz Total 2-3 MV 200 kV/m 8 straights for RF. Requirements for RF. Saw-Tooth RF

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PRISM RF

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  1. PRISM RF C. Ohmori　（KEK) PRISM FFAG workshop@Imperial College

  2. Contents • PRISM RF • Introductions • Present status, RF for a beam • RF for 6 cell ring • Upgrade plan • EMMA RF • RF system for PRSIM PRISM FFAG workshop@Imperial College

  3. Requirements for RF • High voltage at 3.8 MHz • Total 2-3 MV • 200 kV/m • 8 straights for RF PRISM FFAG workshop@Imperial College

  4. Requirements for RF • Saw-Tooth RF • Linear RF bucket • Composed of 3 harmonics PRISM FFAG workshop@Imperial College

  5. MA cavity for PRISM • High field gradient at low frequency • Wideband (low Q) • Thin cavity (about 30 cm / cavity ) • Use the maximum size for MA cores (1.7m X 1m) • Very low duty RF system • To reduce the cost • Small tetrodes for the end stage • Small APS (anode power supply) PRISM FFAG workshop@Imperial College

  6. High Field Gradient : around 200 kV/m few MV RF for quick phase rotation (around 1.5 us) Dedicated system for pulse operation (low duty : 0.1%) PRISM FFAG workshop@Imperial College

  7. Characteristics of Magnetic Cores Ferrites シャントインピーダンスに比例 High Loss Effect 200V/div, 5ms/div 2000 Gauss Magnetic Alloys 電圧に比例 PRISM FFAG workshop@Imperial College

  8. 1.7m 1m 1.0m PRISM FFAG workshop@Imperial College

  9. Thin RF cavities surrounded by RF amplifiers PRISM FFAG workshop@Imperial College

  10. Dedicated system for low duty • AMP • Use small tubes • Works for short moment; 1-2 us X 1 kHz • For 1 kHz repetition, need to minimize RF-ON time • 99 % of time: zero anode current, 99.9%:zero RF output • Cavity loss : few kW • Tube loss : few ten kW • APS • Old fashion to minimize cost: Crowbar, 3-phase Full-wave rectification • J-PARC :1MW system, no crowbar, switching with IGBT • Supplies power to 4 AMPs, several MW in total. PRISM FFAG workshop@Imperial College

  11. Cathode current ＲＦＯＮ Tube ON by modulation of CG voltage PRISM FFAG workshop@Imperial College

  12. Dedicated RF system for low duty J-PARC 600kW tube AMP 500kW output 1.4X1.0X2.4m 100kW tube AMP, >1MW output 1.4X0.7X0.8m Multi-MW APS, 1X1.5X2.0m 1.2 MW APS for J-PARC, 4.5X2X2.7m PRISM FFAG workshop@Imperial College

  13. STATUS of PRISM RF • RF frequency 5 -> 3.8 MHz (larger circumference)->2 MHz for a beam • AMP has modified for low frequency operation. • Achieved 30 kV/gap, 100 kV/m. • Core impedance : 100 W/core @2 MHz 128 W/core @3.8 MHz 244W/core@ 18 MHz • Number of cores: 4 instead of 6 (design : 6 cores, total 1kW) PRISM FFAG workshop@Imperial College

  14. 6 cell ring PRISM FFAG workshop@Imperial College

  15. PRISM FFAG workshop@Imperial College

  16. Gap voltage PRISM FFAG workshop@Imperial College

  17. 6 cell PRISM • Test using a beam has been carried out. • At 2 MHz, 100 kV/m was achieved • Saw-tooth will be tried. PRISM FFAG workshop@Imperial College

  18. Hybrid RF system • Proposed by A. Schnase. • Combination of MA cavity with a resonant circuit composed by inductor and capacitor. • Developed for J-PARC RCS cavities. f=1/2p√LC 1/L=1/Lcore+1/Lind Q=Rp/wL Rp: shunt J-PARC: add C and L to control Q and f PRISM : add L to control f PRISM FFAG workshop@Imperial College

  19. Parallel inductor for J-PARC Inside of PRISM AMP PRISM FFAG workshop@Imperial College

  20. Expected impedance with parallel inductor Total C =180pF Hybrid (+40 uHinductor) Hybrid (+ 8 uH inductor) Hybrid ( +18 uH), 3.8 MHz PRISM FFAG workshop@Imperial College

  21. Saw-Tooth : • RF Cavity will be a wideband cavity. • But, bandwidth of AMP is still limited (1/RC). • To obtain high RF voltage, a large drive voltage is still required for CG-Cathode. • Solutions • Low duty high power DAMP based on CERN/J-PARC DAMP. • Drive from both CG and Cathode is possible in case of short pulse operation. • Narrow bandwidths are enough for both CG and Cathode. -> save the cost for Driver AMP • Both need test. PRISM FFAG workshop@Imperial College

  22. X-ray Over 30 kV anode voltage, soft X-ray was observed. Additional X-ray shields were add on vacuum tubes and AMP. Most sensitive X-ray detector was used. PRISM FFAG workshop@Imperial College

  23. Upgrade Plan • High Field Gradient • Cost reduction PRISM FFAG workshop@Imperial College

  24. Improvements of cavity impedance • Improvements of cavity cores • X 2 by annealing under magnetic field for thinner ribbon • Small cores : OK • Large core ? ∝shunt impedance PRISM FFAG workshop@Imperial College

  25. How to improve • MA consists of Fe, Si, B, Cu and Nb. • Amorphous ribbon (<20 mm) is annealed and crystallized. • Combination of magnetic field during annealing and thinner ribbon (13 mm) • The small crystal has an axis magnetized easily. By the special annealing, the axis is equal. • But relation between core impedance and this effect is not clear. • Small cores : proved by Hitachi Metal • Large core : need big magnet and special oven. => Appling JSPS grant to produce these special core in KEK. B-H curve of MA core produced by annealing with/without magnetic field. (by Hitachi Metal) PRISM FFAG workshop@Imperial College

  26. Decayed positron N_backward N_forward Polarized μ finemet ‖cylinder ⊥cylinder Asymetry =(N_forward - N_backward)/(N_forward+N_backward) PRISM FFAG workshop@Imperial College

  27. PRISM FFAG workshop@Imperial College

  28. PRISM FFAG workshop@Imperial College

  29. It clearly showed the effects on magnetic properties by applying the magnetic field during the crystallization process in production. • It suggests that the magnetic axis of nano-scale crystalline in FT3L are aligned to the direction of the magnetic field during the annealing process. • In the case that the initial spin direction of implanted muons is perpendicular to the assumed easy-axis of nano-crystalline FT3L, the polarization of muons showed a quite fast damping. • In contrast, a slow relaxing time spectrum was obtained when the initial direction was aligned with the axis along which the magnetic field had been applied during the annealing, suggesting that the muon polarization is retained due to the local magnetic field. • On the other hand, such a drastic change was not seen in the case of FT3M. It turned out, however, that an anisotropic behaviour against the initial muon spin direction in FT3M was still observed, in spite of the absence of the magnetic field during the production. • The muon implanted in parallel to the ribbon surface depolarizes slightly faster than that implanted in perpendicular. • This may suggest that the shape of MA, e.g. thickness, causes magnetic anisotropy. • It hints that the characteristics of FT3L depends more on the thickness of ribbon than on an expected eddy current effect. PRISM FFAG workshop@Imperial College

  30. High impedance core • Further experiments using mSR to confirm the effects of ribbon thickness. • We will Make larger cores to confirm the impedance measurements. • 27 cm size cores will be produced in this summer. • These R&D are also important for high intensity accelerators (J-PARC RCS, MR, ISIS-upgrade, CSNS etc.). • To confirm finally, it is important to build a cavity structure. PRISM FFAG workshop@Imperial College

  31. Cost issues • So far, 6 cores were necessary to generate 50 kV. However, 4 cores will be enough to generate 60 kV in case of high impedance cores. • Achieving 1 kW impedance will make a system design similar to original one (6 cores, 5 MHz). • The cavity cost seems to be larger than other cost in case of PRISM. Higher voltage per core is preferable. • However, total cost to obtain 2MV is still expensive. PRISM FFAG workshop@Imperial College

  32. conclusions • Beam test was performed by using PRISM rf cavity • Demonstrate > 100 kV/m. • Also plan to test saw-tooth RF • To reduce the rf cost, developments of high impedance cores are important. PRISM FFAG workshop@Imperial College

  33. EMMA MA System • * Many FFAG applications require slow acceleration • * Non-scaling FFAGs cross many resonances  - Nonlinear resonances  - Imperfection resonances • * Resonances damage beam more when you cross them slowly • * There is thus a minimum rate at which you can cross resonances  - May depend on magnitude of errors • * Low-frequency RF to allow slow acceleration  - EMMA as-is only allows very rapid acceleration  - Primarily due to high-frequency RF system • * Accelerate rapidly then reduce rate  - Start with 100 turns to insure success  - Reduce acceleration rate and study effects PRISM FFAG workshop@Imperial College

  34. Parameters PRISM FFAG workshop@Imperial College

  35. EMMA MA CAVITY PRISM FFAG workshop@Imperial College

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