The First Beam Acceleration Test Using High Gradient Cavity at Himac

The HGC loaded with MA cores has been developed[1] for the JHF (Japan Hadron Facility) proton synchrotrons. The maximum voltage of 20 kV has been obtained by the cavity of 40 cm in length. The cavity was driven by a pushpull amplifier using two 150 kW tetrodes. The frequency sweeping from 1 to 5 MHz has been achieved without any tuning circuit because of its broadband characteristics of the MA-loaded cavity[2]. The cavity has been installed in the HIMAC[3] for the beam acceleration to examine the characteristics of the broad-band system. Two major changes has been carried out for both cavity and amplifier. One is to reduce the number of cores to increase the resonant frequency of the cavity. Another is to replace the amplifier. A push-pull amplifier with two 30 kW tetrodes was newly employed, which covered the required rf frequency range of 1–8 MHz for accelerating heavy ions. The beam acceleration of He, C, Ne and Si ions was successfully carried out and the results are reported in this paper. The fundamental rf and higher harmonics could be driven by the cavity simultaneously because the cavity has a broad impedance, which covers these frequencies. Further improvement of the acceleration efficiency is expected by adding the higher harmonics[4].