Download - RF System for Bunch Rotation
RF System for Bunch Rotation
C. Ohmori ( KEK)
Contents
• PRISM RF– Introductions– Present status– RF for 6 cell ring– Upgrade plan
• High Duty RF system for FFAG– Medical application– Experiences from J-PARC
Requirements for RF
• High voltage at 3.8 MHz – Total 2-3 MV– 200 kV/m– 8 straights for
RF
•Saw-Tooth RF–Linear RF bucket–Composed of 3 harmonics
Requirements for RF
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
– Small tetrodes for the end stage
– Small APS (anode power supply)
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%)
Characteristics of Magnetic Cores
1.00E+09
1.00E+10
1.00E+11
1 10 100 1000 10000
Brf[Gauss]
up'Qf
SY2
N5C
4M2-302
FT-small
FT-large200V/div, 5ms/div
High Loss Effect
Magnetic Alloys
Ferrites
2000 Gauss
シャントインピー
ダンス
に比例
電圧に比例
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.
Tube ON
RFON
Cathode current
100kW tube AMP, >1MW output1.4X0.7X0.8m
J-PARC600kW tube AMP500kW output1.4X1.0X2.4m
APS, 1X1.5X2.0m APS for J-PARC, 4.5X2X2.7m
Dedicated RF system for low duty
STATUS of PRISM RF• RF frequency 5 -> 3.8 MHz (larger circumference)• Tested at 2-3 MHz with a test cavity• Achieved 42 kV/gap by test cavity• Tube AMP:60A(design value)->70A as a RF
current @ 2-3MHz
• Cavity shroud is completed. Start to install cores. • Core impedance : about 135 /[email protected]• Number of cores: 4 instead of 6 (design : 6 cores,
total 1k)
• 6 cell PRISM– Test using beam– 1(or 2,3) MHz, 100 kV/m– Saw-tooth
• PRISM– 3.5 MHz, about 200 kV/m– Saw-tooth
• Upgrade Plan– Cost, Higher field gradient
6 Cell ring• To test bunch rotation using beam• Low energy, low RF frequency • Few ten kV is required to observe bunch motion.• Problems
– Low impedance@ low frequency because of uncut cores
• Expected voltage @1MHz : 352 X 60 A= 21 kV
– A Solution : use 2 RF AMPs to drive 1 cavity.• Expected voltage : 352 X 120 A =42 kV to prove 100kV/m
Another solution : use parallel inductor scheme established through J-PARC R&D for high frequency.
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/LRp: shunt
Parallel inductor for J-PARC
Inside of PRISM AMP
-4.00E+02
-2.00E+02
0.00E+00
2.00E+02
4.00E+02
6.00E+02
8.00E+02
0 2 4 6 8 10 12
RXZ
-3.00E+02
-2.00E+02
-1.00E+02
0.00E+00
1.00E+02
2.00E+02
3.00E+02
4.00E+02
5.00E+02
0 2 4 6 8 10 12
RXZ
-4.00E+02
-3.00E+02
-2.00E+02
-1.00E+02
0.00E+00
1.00E+02
2.00E+02
3.00E+02
4.00E+02
5.00E+02
6.00E+02
0 2 4 6 8 10 12
RXZ
-4.00E+02
-3.00E+02
-2.00E+02
-1.00E+02
0.00E+00
1.00E+02
2.00E+02
3.00E+02
4.00E+02
5.00E+02
6.00E+02
0 2 4 6 8 10 12
RXZ
Total C =100pF Hybrid (13 uH)
Total C =200pF Hybrid (+30uH inductor)
Expected impedance with parallel inductor
PRISM CAVITY for 6 cell ring• 4 Cores, around 3 MHz
• Expected cavity impedance : 500 • More than 35 kV (>100kV/m) seems
possible (70A X 500 ).
Saw-Tooth : Dual Drive System
• 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 required for CG-Cathode.
• Usually, AMP is driven from CG or Cathode. • 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– But, need test.
Upgrade Plan• High Field Gradient
• Cost reduction
Improvements of cavity impedance
• Hybrid cavity with ceramic cavity
• Improvements of cavity cores– X 2 by annealing
under magnetic field for thinner ribbon
– Small cores : OK
– Large core ?
uQf (é•ê´ëÃÉRÉAÇÃì¡ê´Åj
0
2
4
6
8
10
12
14
0 1 2 3 4 5 6
frequencyÅ@ÅiMHÇöÅj
uQf (GHz)
uQf(FT3L,13um)uQf(FT3L,18um)uQf(FT3M,18um)
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 FY2007 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)
Ceramic Cavity • Proposed by J. Griffin.• Low frequency air core cavity with a ceramic capacitor to re
sonate.• Titanium Oxide capacitor was tested. 50kVDC (tested with
60kVDC). 1200pF. Electrodes are O.D. 121mmX I.D. 52mm, Thickness of ceramic is 14mm.
• Supported by JSPS money. Purpose : bunch rotation with low rep. rate.
• Small test cavity :30 cm X 30cm• 4 k, Q=700, fres=7 MHz• High power test is planned. • High rep. rate : Hybrid cavity system with MA cavity.
– Effective Q => below 100.
conclusions
• We start assembling PRISM rf cavity
• Demonstrate > 100 kV/m in April/May
• Also plan to test saw-tooth RF
• For general application, design of FFAG cavity is presented.
High duty RF system for FFAG
• General applications (beam acceleration )
• High duty (100 %)
• Preliminary design based on experiences at the J-PARC ring RF– Direct water cooling– High average power
Direct Water Cooling • Effective Cooling
Scheme• Adopted for J-PARC
Ring RF– 1W/cc, more than
1000 H test run
• COSY, CERN-LEIR, HIMAC-MA
• Design for FFAG cavity
Power Consumption for FFAG cavity • 10MeV->140 MeV• 1.5->4 MHz• 6 kV/gap, 100 % duty• 4 X PRISM-size cores
– 1.7 m X 1m X 3cm– Size of Cavity :2m X 1.2 m X 0.4-0.5 m
• 45 kW/gap, 11.25 kW/core• 0.32W/cc (av.), 0.54 W/cc (Max.) < 1 W/cc
Water I nWater Out1. 9m1. 2m
50cm
Technical key issues• Good immersion
– Mechanical strength– Cause of pin holes
• Good coating– J-PARC : epoxy+glass fiber
• Careful treatment of core surface– Scratch of MA surface may make
local hot spots, destroy coating and reduce core impedance
– Dusts on MA surface may make very local hot spots and destroy coating