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.). Frequency Environments Materials But, these are not independent ! –Low duty-High voltage vs High duty-Medium voltage

Magnetic Cores for Cavity Magnetic Alloys Ferrites Requirements for PRISM B=V/  S=400Gauss

PRISM Cavity Design. APS AMP Cavity By C. Ohmori, Y. medium Beam Pipe Side View 33cm

RF Cavities Field Gradient of Cavities for Proton Synchrotrons Ferrite Cavities JKJ RF Cavities KEK-PS MA Cavity High Gap Voltage (X 3) & Short Cavity (X 2) Very High Gradient for very short moment (10  s) !

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)

Limit for High Field Gradient So 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.

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 water150 MeV FFAG –Direct Water coolingJ-PARC, CERN-LEIR

Forced Air cooling At KEK-PS booster, ferrite cavities have been replaced by MA cavities. –20 Hz, MeV –30-40 kV –Duty : 25-30% –Impedance ? –Power dissipation ? Pop FFAG uses air cooling.

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 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.

FNAL J-PARC R&D

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: kW/6 cores X 300 H –Cut core (medium Q): kW/6 cores X 150 H –By combination of non-cut and med-Q, hybrid cavity for RCS –Cut core (high Q): 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

Capacitance effects by water Direct Cooling Indirect Water Cooling

J=PARC RCS Tunnel

CERN-LEIR Cavity （ 2005/4 ）