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 5.8MeV∕u with intensities of more than 1pμA (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 36to76.4MHz, whereas the last four are operated at a fixed frequency of 75.5MHz. The design study started in 1997 and the booster was commissioned in 2001. The total voltage gain of the booster ever achieved is 11MV, which is 70% of the designed value of 16MV. 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.
The sector magnets of the K2500-MeV Superconducting Ring Cyclotron (SRC), which is under construction for the RIKEN RI Beam Factory, are described. The SRC consists of six sector magnets, four rf resonators, etc. Each sector magnet is 7.2 m in length and 6 m in height and 800 t (metric ton) in weight; the sector angle is 25 deg. The required maximum magnetic field is 3.8 T. The superconductor for the main and trim coil has a rectangular shape (8 mm by 15 mm) consisting of a Rutherford-type NbTi cable located at the center of an Al-alloy stabilizer housing.
The main coil is bath-cooled and the trim coil is indirectly cooled. Each component of the sector magnet as well as the cryogenic cooling system was completed in the spring of 2003.Index Terms-Bath-cooling and indirect-cooling, sector magnet, superconducting ring cyclotron, superconductor with Al-alloy stabilizer.
We successfully produced intense beams of highly charged ions from various kind of gaseous elements, organic metallic compounds (by MIVOC method), and solid materials from RIKEN 18 GHz ECRIS. (e. g. 160eµA of Ar 11+ , 5eµA of Ar 16+ , 80 eµA of Fe 13+ ). The ion confinement time of highly charged ions was also determined under the pulsed mode operation.
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