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

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 reducing the ribbon thickness and applying a transverse magnetic field during annealing. In this paper, we study the effects of transverse field annealing on the MA core shunt impedance by comparing two kinds of MA cores, those are the FT3M core that is annealed without any magnetic fields and the FT3L core that is annealed with a transverse magnetic field. The FT3L core shows the higher shunt impedance than the FT3M core. By applying the transverse magnetic field during annealing, the magnetization processes of the FT3L core 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.