PRISM RF

C. Ohmori 　（ KEK)

2009/7/2 PRISM FFAG workshop@Imperial College

ContentsPRISM RF

IntroductionsPresent status, RF for beamRF for 6 cell ringUpgrade planEMMA RFRF system for PRSIM


Requirements for RFHigh voltage

at 3.8 MHz Total 2-3 MV200 kV/m8 straights

for RF


•Saw-Tooth RF–Linear RF bucket–Composed of 3 harmonics

Requirements for RF


MA cavity for PRISMHigh field gradient at low frequencyWideband (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 costSmall tetrodes for the end stageSmall 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

up'Q

f

Brf[Gauss]

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


1.7m

1m

1.0m


Thin RF cavities surrounded by RF amplifiers2009/7/2 PRISM FFAG workshop@Imperial College

Dedicated system for low dutyAMP

Use small tubesWorks for short moment; 1-2 us X 1 kHz

For 1 kHz repetition, need to minimize RF-ON time99 % of time: zero anode current,

99.9%:zero RF output Cavity loss : few kW Tube loss : few ten kW

APSOld fashion to minimize cost: Crowbar, 3-

phase Full-wave rectification J-PARC :1MW system, no crowbar, switching with

IGBTSupplies power to 4 AMPs, several MW in

total.


Tube ON by modulation of CG voltage

ＲＦＯＮ

Cathode current


100kW tube AMP, >1MW output1.4X0.7X0.8m

J-PARC600kW tube AMP500kW output1.4X1.0X2.4m

Multi-MW APS, 1X1.5X2.0m 1.2 MW APS for J-PARC, 4.5X2X2.7m

Dedicated RF system for low duty


STATUS of PRISM RFRF frequency 5 -> 3.8 MHz (larger

circumference)->2 MHz for beamAMP has modified for low frequency

operation.Achieved 30 kV/gap, 100 kV/m.

Core impedance : 100 /core @2 MHz128 /core @3.8 MHz 244/core@ 18 MHz

Number of cores: 4 instead of 6 (design : 6 cores, total 1k)


6 cell ring



Gap voltage


6 cell PRISMTest using beam has been carried out.At 2 MHz, 100 kV/m was achievedSaw-tooth will be tried.


Hybrid RF systemProposed 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 AMP2009/7/2 PRISM FFAG workshop@Imperial College

Hybrid (+ 8 uH inductor) Hybrid ( +18 uH), 3.8 MHz

Total C =180pF Hybrid (+40 uH inductor)

Expected impedance with parallel inductor


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 AMPBoth need test.


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.


Upgrade PlanHigh Field GradientCost reduction


Improvements of cavity impedance

Improvements of cavity cores X 2 by annealing

under magnetic field for thinner ribbon

Small cores : OK Large core ?

uQf (磁性体コアの特性）

0

2

4

6

8

10

12

14

0 1 2 3 4 5 6

frequency MH（ｚ）

uQf (

GH

z)

uQf(FT3L,13um)uQf(FT3L,18um)uQf(FT3M,18um)

∝sh

unt i

mpe

danc

e


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 MetalLarge 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)


Polarized μ

N_forwardN_backward

finemet‖cylinder

⊥cylinder

Decayed positron

Asymetry =(N_forward - N_backward)/(N_forward+N_backward)2009/7/2 PRISM FFAG workshop@Imperial 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. 2009/7/2 PRISM FFAG workshop@Imperial College

High impedance coreFurther 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.


Cost issuesSo 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.


conclusions

Beam test was performed by using PRISM rf cavity

Demonstrate > 100 kV/m.Also plan to test saw-tooth RFTo reduce the rf cost, developments of high

impedance cores are important.


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


Parameters frequency 18 MHz =1.3 GHz/72

frequency sweep 3 %

Total Voltage 100 kV per turn 100 turns/cycle

Number of cavities 3

Voltage 33 kV

Length of cavity 10 cm

Number of MA cores 2 per cavity

Size of MA core 27 cm O.D, 10 cm I.D x 2.5 cm

MA core Cut core

Q-value About 20

Cavity impedance 700(1.4 k)

Core material FT3M (FT3L)


EMMA MA CAVITY


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