Construction of a booster linac for the RIKEN heavy-ion linac

A linac consisting of six rf cavities has been constructed as an energy booster of the RIKEN heavy-ion linac. Various heavy ion beams have been accelerated to 5.8 MeV/u with intensities of more than 1 pmuA (particle microampere) in the continuous-wave mode. The booster cavities are based on a quarter-wavelength resonator of a coaxial structure. The first two cavities are frequency-variable in a range from 36 to 76.4 MHz, whereas the last four are operated at a fixed frequency of 75.5 MHz. The design study started in 1997 and the booster was commissioned in 2001. The total voltage gain of the booster ever achieved is 11 MV, which is 70% of the designed value of 16 MV. The high-intensity beams from the booster have been successfully applied to a systematic study on the synthesis of superheavy elements. The beam energy from the ring cyclotron has also been increased, owing to the additional velocity gain provided by the booster. (C) 2005 American Institute of Physics.