Present status of TIARA at QST

The Takasaki Ion accelerators for Advanced Radiation Application (TIARA) facility consists of four ion accelerators (the AVF cyclotron with a K value of 110 MeV, the 3 MV tandem accelerator, the 3 MV single-ended accelerator, the 400 kV ion implanter). These accelerators have been providing ion beams with wide energy range and various ion species for many researchers in materials science and biotechnology fields. Regarding the cyclotron, a layer short of the upper main coil occurred in 2016. In order to continue the operation, two pairs of upper and lower layers including the shorted layer were bypassed even though maximum magnetic field decreased by 20%. After that two main coils have been renewed to complete the restoration, and it took nine months. For the electrostatics accelerators, the high-intensity C₆₀ negative ion source has been developed, and it was found that simultaneous sublimation of C₆₀ and cesium iodide improves the amount of beam current and its stability. This paper describes the recent operational status of the accelerators, major technical developments and maintenance of the accelerators. (author)