Development of medium-frequency cavity loaded with multi-ring magnetic alloy cores cooled by chemically inert liquid

Magnetic alloys (MAs) are commonly applied in the radio-frequency (RF) cavities of proton synchrotrons. The high saturation permeability and Curie temperature of MAs facilitate the development of RF cavities with large accelerating gradients that could not be achieved with ferrite. The conventional MA core is a disk-shaped toroid made by winding MA ribbons. Here, we propose a multi-ring core structure that consists of three concentrically arranged toroidal ring cores of different radial sizes. Neither epoxy resin impregnation nor a waterproof coating is applied to the cores, and thus the thermal stress during high-power operation is expected to be relaxed. A set of multi-ring cores is sandwiched between two glass-epoxy plates with flow channels. This modular structure increases the velocity of the coolant flow, making the flow turbulent to obtain the desired cooling efficiency. Coolant-induced corrosion of the Fe-based MA is prevented by adopting a low-viscosity, chemically inert, and electrically insulating liquid. The RF and thermal designs of a cavity loaded with multi-ring cores are presented and two types of test cavity are developed. A series of high-power tests demonstrate stable operation with the designed performance. The results of experimental performance tests for two cavities loaded with multi-ring MA cores cooled by a chemically inert liquid are reported.