Limits of MA cavity

1. Limits of MA cavity C. Ohmori KEK

2. 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

3. Magnetic Cores for Cavity Ferrites Magnetic Alloys Requirements for PRISM B=V/wS=400Gauss

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

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

6. RF system R&D • 43 kVp/gap using 700 W 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)

7. 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 mm=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, mQf=7x10^9. But, it will be more than 10^10 at 10MHz. RIKEN reports that MA can be used at 20 MHz and higher mQf. 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.

8. 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

9. Forced Air cooling • At KEK-PS booster, ferrite cavities have been replaced by MA cavities.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.

11. 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.

12. FNAL J-PARC R&D

13. 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

14. Capacitance effects by water Indirect Water Cooling Direct Cooling

18. J=PARC RCS Tunnel

19. CERN-LEIRCavity（2005/4）