Development of RF acceleration system for 150Â MeV FFAG accelerator

An RF accelerating system was developed for the 150 MeV FFAG accelerator to demonstrate rapid cycling acceleration. The 150 MeV FFAG accelerator has been developed as a prototype for various applications, such as proton cancer therapy. To achieve rapid cycling acceleration, a high-field gradient and a broadband impedance of the RF cavity were necessary. Therefore, we employed a magnetic alloy (MA) for a core material. The required field gradient and the bandwidth were 35 kV/m and 3.0±1.5MHz, respectively. Because of the strong fringing field of the focusing magnets of the FFAG accelerator, the RF cavity had to be magnetically shielded. An effective cooling system for the MA cores was also needed because of the large power dissipation of more than 1W/cm3. We have developed an RF system satisfying these requirements and successfully demonstrated a rapid cycling acceleration of 100 Hz.