C. Ohmori （ KEK) 2009/7/2PRISM FFAG College

Contents PRISM RF Introductions Present status, RF for  beam RF for 6 cell ring Upgrade plan EMMA RF RF system for PRSIM 2009/7/2PRISM FFAG College

Requirements for RF High voltage at 3.8 MHz Total 2-3 MV 200 kV/m 8 straights for RF 2009/7/2PRISM FFAG College

Saw-Tooth RF –Linear RF bucket –Composed of 3 harmonics Requirements for RF 2009/7/2PRISM FFAG College

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) 2009/7/2PRISM FFAG College

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%) 2009/7/2PRISM FFAG College

Characteristics of Magnetic Cores 200V/div, 5ms/div High Loss Effect Magnetic Alloys Ferrites 2000 Gauss 電圧に比例 2009/7/2PRISM FFAG College

1.7m 1m 1.0m 2009/7/2PRISM FFAG College

Thin RF cavities surrounded by RF amplifiers 2009/7/2PRISM FFAG College

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. 2009/7/2PRISM FFAG College

Tube ON by modulation of CG voltage ＲＦＯＮ Cathode current 2009/7/2PRISM FFAG College

100kW tube AMP, >1MW output 1.4X0.7X0.8m J-PARC 600kW tube AMP 500kW output 1.4X1.0X2.4m Multi-MW APS, 1X1.5X2.0m 1.2 MW APS for J-PARC, 4.5X2X2.7m Dedicated RF system for low duty 2009/7/2PRISM FFAG College

STATUS of PRISM RF RF frequency 5 -> 3.8 MHz (larger circumference)->2 MHz for  beam AMP has modified for low frequency operation. Achieved 30 kV/gap, 100 kV/m. Core impedance :100  MHz 128  MHz 244  18 MHz Number of cores: 4 instead of 6 (design : 6 cores, total 1k  ) 2009/7/2PRISM FFAG College

6 cell ring 2009/7/2PRISM FFAG College

2009/7/2PRISM FFAG College

Gap voltage 2009/7/2PRISM FFAG College

6 cell PRISM Test using  beam has been carried out. At 2 MHz, 100 kV/m was achieved Saw-tooth will be tried. 2009/7/2PRISM FFAG College

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=1/2  √LC 1/L=1/Lcore+1/Lind J-PARC: add C and L to control Q and f PRISM : add L to control f Q=Rp/  L Rp: shunt 2009/7/2PRISM FFAG College

Parallel inductor for J-PARC Inside of PRISM AMP 2009/7/2PRISM FFAG College

Hybrid (+ 8 uH inductor) Hybrid ( +18 uH), 3.8 MHz Total C =180pF Hybrid (+40 uH inductor) Expected impedance with parallel inductor 2009/7/2PRISM FFAG College

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. 2009/7/2PRISM FFAG College

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. 2009/7/2PRISM FFAG College

Upgrade Plan High Field Gradient Cost reduction 2009/7/2PRISM FFAG College

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 2009/7/2PRISM FFAG College

How to improve MA consists of Fe, Si, B, Cu and Nb. Amorphous ribbon (<20  m) is annealed and crystallized. Combination of magnetic field during annealing and thinner ribbon (13  m) 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) 2009/7/2PRISM FFAG College

Polarized μ N_ forward N_ backward finemet ‖ cylinder ⊥ cylinder Decayed positron Asymetry =(N_forward - N_backward)/(N_forward+N_backward) 2009/7/2PRISM FFAG College

2009/7/2PRISM FFAG College

2009/7/2PRISM FFAG College

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. 2009/7/2PRISM FFAG College

High impedance core Further experiments using  SR 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. 2009/7/2PRISM FFAG College

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 k  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. 2009/7/2PRISM FFAG College

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. 2009/7/2PRISM FFAG College

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 2009/7/2PRISM FFAG College

Parameters frequency18 MHz=1.3 GHz/72 frequency sweep3 % Total Voltage100 kV per turn100 turns/cycle Number of cavities3 Voltage33 kV Length of cavity10 cm Number of MA cores2 per cavity Size of MA core27 cm O.D, 10 cm I.D x 2.5 cm MA coreCut core Q-valueAbout 20 Cavity impedance 700  (1.4 k  ) Core materialFT3M (FT3L) 2009/7/2PRISM FFAG College

EMMA MA CAVITY 2009/7/2PRISM FFAG College