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Test of Cryocooler-Cooled RE-123 Magnet on HIMAC Beam Line in S-Innovation Program

A cryocooler-cooled high-temperature superconducting magnet was constructed, and it was tested on the beam line of the heavy ion medial accelerator in Chiba (HIMAC). The magnet consists of a pair of four-stacked racetrack coils wound with RE-123 coated conductor that are plated with 41-μm copper for protection. The magnet has a room temperature beam duct, at which 2.4 T of magnetic field is generated, whereas the maximum magnetic field to which coated conductors are exposed is approximately 4 T. The magnetic field in the beam duct was measured and calculated to examine its stability, which might have been affected by shielding currents in the coated conductors. On the beam line of the HIMAC, at first, the beam guiding by the magnet was demonstrated. The measured beam-guiding characteristics were compared with the beam tracking calculations. Next, a carbon ion beam was injected intentionally into the RE-123 coils of the magnet to simulate the incidents of uncontrolled beam injection into accelerator magnets. Prior to this test, the possible heat deposition to the coil by the beam injection was calculated, and the feasibility of quench protection using a dump resistor was studied through quench experiments using short pieces of the RE-123 coated conductors.