Mechanisms of increasing of the magnetic alloy core shunt impedance by applying a transverse magnetic field during annealing

Nomura, Masahiro  ; Shimada, Taihei ; Tamura, Fumihiko   ; Yamamoto, Masanobu   ; Hara, Keigo*; Hasegawa, Katsushi*; Omori, Chihiro*; Toda, Makoto*; Yoshii, Masahito*

In the J-PARC synchrotrons, Magnetic Alloy (MA) cores loaded RF cavities are employed to achieve a high field gradient. We are successful to increase the shunt impedance of the MA cores for the Main Ring synchrotron RF cavities by applying a transverse magnetic field during annealing. The shunt impedances of the cores with transverse field annealing are around 50% higher than the cores without one. By applying the transverse magnetic field during annealing, the magnetization processes occur by mainly magnetization rotations, and consequently the core loss is reduced and the relative complex permeability shows an excellent frequency behavior. The MA core shunt impedance is increased by those improvements of the magnetic properties.