Toward Superconducting Electron Accelerators for Various Applications

A 300 MeV electron linac is constructed in 1967 at Tohoku University for advanced research on nuclear physics, radiochemistry and neutron science. A very high beam repetition rate of 300 pps is employed to achieve a duty factor of more than 0.1%. Although substantial parts of the linac sadly collapsed as a result of the Great East Japan earthquake occurred in 2011, the low-energy part of the linac still supplies high-intensity beams. To expand current research activities, the introduction of a versatile accelerator system that employs superconducting radiofrequency (SRF) cavities have been considered. Because the low surface resistance on these SRF cavities decreases the power dissipated to the cavity walls, the beams can be accelerated with a duty factor as high as 100%. However, the SRF cavities, which are manufactured from niobium (Nb), need to be operated at cryogenic temperatures of 2 K with a considerably large cryogenic system. Recently it is pointed out that the large heat load could be greatly lowered by replacing the standard Nb cavities with those coated with high-temperature superconductors. The possibility of developing simple and low-cost SRF accelerators based on conduction cooling with a 4 K refrigerator system is anticipated.