Accelerator development for the Japanese Hadron Project and super-conducting CW (Continuous Wave) beam proton linac

The development program for the proton linac of the Japanese Hadron Project (JHP) were formed in order to minimize the beam loss which gives rise to the radioactivity. The power efficiency and the operation stability are important factors to be taken into account. For this purpose the annular-ring coupled structure (ACS) is the ideal choice for the high-energy structure, maintaining both the reasonably high shunt impedance and the axial symmetry. The focusing magnet system made of permanent magnets was developed with sufficient accuracy for a drift-tube linac (DTL). The π-mode stabilizing loop (PISL) for a radio-frequency quadrupole (RFQ) linac was invented in order to eliminate the admixture of the deflecting mode to the accelerating mode. All the ACS, DTL, and RFQ have been tested up to higher than the designed power level with the designed duty factor. The RFQ accelerated the beam up to 3 MeV which equaled the RFQ world record marked in Russia. The design concept of the JHP linac is further extended to the higher-intensity proton linac, resulting in the proposal of the continuous-beam, superconducting proton linac. (author)