Studies of magnetic cores for JHF synchrotrons

Magnetic cores suited for the RF cavities of JHF (Japanese Hadron Facility) synchrotrons have been studied. The shunt impedance of the cavity is required about 2 kΩ/m because of the high acceleration voltage of more than 10 kV/m. The permeability of the core should meet with the RF frequencies of the 3 GeV booster and the 50 GeV ring. Characteristics of several ferrites and a Fe-based soft magnetic alloy composed of amorphous and ultra-fine grain structure have been measured with a test bench. The shunt impedance of the soft magnetic core named “FINEMET” is high enough. It is stable when input RF power is increased, while those of samples of ferrites drop rapidly. The permeability of “FINEMET” strongly depends on the bias current. Because of its low Q value, the bias current is not necessary for its new material. “FINEMET” is considered as one of the most probable candidate for JHF synchrotrons