Limits of MA cavity C. Ohmori KEK. What kind of limit? Voltage Field Gradient Temperature (cooling)...
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Transcript of Limits of MA cavity C. Ohmori KEK. What kind of limit? Voltage Field Gradient Temperature (cooling)...
![Page 1: Limits of MA cavity C. Ohmori KEK. What kind of limit? Voltage Field Gradient Temperature (cooling) –below 200 deg. C for long term (Hitachi Metal Co.).](https://reader036.fdocuments.in/reader036/viewer/2022062422/56649ed95503460f94be6f73/html5/thumbnails/1.jpg)
Limits of MA cavity
C. Ohmori KEK
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What kind of limit?• Voltage• Field Gradient• Temperature (cooling)
– below 200 deg. C for long term (Hitachi Metal Co.).
• Frequency• Environments• Materials
• But, these are not independent !– Low duty-High voltage vs High duty-Medium voltage
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Magnetic Cores for Cavity
1.00E+09
1.00E+10
1.00E+11
1 10 100 1000 10000
Brf[Gauss]
up'Qf
Magnetic Alloys
Ferrites
Requirements for PRISMB=V/S=400Gauss
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PRISM Cavity Design
.
APS
AMP
Cavity
By C. Ohmori, Y. medium
Beam Pipe
Side View
33cm
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RF CavitiesField Gradient of Cavities for Proton
Synchrotrons Proton Synchrotron RF System
0
10
20
30
40
50
60
0 2 4 6 8 10 12
Frequency (MHz)
Field Gradient (kV/m)
SATUNE
MIMAS
CERN PSB
CERN PS
AGS
ISIS
KEK BSTR
KEK PS
JKJÅ@50GeV MR
JKJ Å@3GeV RCS
50GeV MR Upgrade
KEK-HGC
Ferrite Cavities
JKJ RF CavitiesKEK-PS MA Cavity
Proton Synchrotron RF System
0
50
100
150
200
250
0 2 4 6 8 10 12
Frequency (MHz)
Field Gradient (kV/m)
SATUNE
MIMAS
CERN PSB
CERN PS
AGS
ISIS
KEK BSTR
KEK PS
JKJÅ@50GeV MRJKJ Å@3GeV RCS 50GeV MR UpgradeKEK-HGC
PRISM
High Gap Voltage (X 3) & Short Cavity (X 2)Very High Gradient for very short moment (10s) !
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RF system R&D
• 43 kVp/gap using 700 test MA cavity:
• Equivalent to 150kV/m seems possible by 33 cm-MA cavity at 5 MHz
• Design goal (60 A RF current) of AMP was achieved.
• Very compact design for AMP and APS.
RF voltage at the gap (red line)
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Limit for High Field GradientSo far, up to 2 kG, we have tested for Brf.Insulation using SiO2 can stand few volts.
(1 volt/20 m=50kV/m in transverse direction.)
For PRISM operation (0.1% duty), 150 kV/m seems acceptable.1%-duty seems acceptable by the forced-air cooling.
Power amplifier and driving scheme give another boundary.
At 5 MHz, Qf=7x10^9. But, it will be more than 10^10 at 10MHz.RIKEN reports that MA can be used at 20 MHz and higher Qf.
More field gradient at higher frequency ?
But, MA is affected by outer magnetic field. Few hundreds gauss seems dangerous from the experience of 150 MeV FFAG.
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Limits for high duty operation• Cooling of MA cores is main issue.• But, reduction of impedance happens by
environmental conditions (capacitance and magnetic field)
• Cooling schemes– Air KEK-PSBooster
– Indirect water 150 MeV FFAG
– Direct Water cooling J-PARC, CERN-LEIR
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Forced Air cooling• At KEK-PS booster, ferrite cavities have been
replaced by MA cavities.– 20 Hz, 40-500 MeV– 30-40 kV– Duty : 25-30%– Impedance ?– Power dissipation ?
• Pop FFAG uses air cooling.
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Indirect Cooling• J-PARC R&D shows 5 kW/core (80 cm OD) seems
acceptable without significant impedance reduction. – But, 5kW is not enough for J-PARC– Conflict between cooling efficiency and impedance.
• 150 MeV FFAG can be operated with 25-50 Hz repetition. Cavity impedance is reduced by the magnetic field.
• FNAL MA cavity• New HIMAC MA cavity (Toshiba core)• Saclay
• Possible to use at high frequency if you design carefully.
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FNAL
J-PARCR&D
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Direct water cooling• Put cores in the water jacket.
– J-PARC, COSY, CERN-LEIR
• J-PARC Cores are coated by epoxy with 0.2 mm thickness. • Three different core configurations
– Non cut core: 50-60 kW/6 cores X 300 H– Cut core (medium Q): 50-60 kW/6 cores X 150 H– By combination of non-cut and med-Q, hybrid cavity for RCS– Cut core (high Q): 50-80 kW/6 cores X 100 H for MR– Requirements : 45 kW for non-cut and mid-Q, 50- kW for high Q.– Not much impedance reduction by water below 3 MHz. But, not
higher than 4 MHz because of capacitance by water
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Capacitance effects by water
Direct Cooling Indirect Water Cooling
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J=PARC RCS Tunnel
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CERN-LEIR Cavity ( 2005/4 )