2020 年 55 巻 2 号 p. 89-97
A cryocooler-cooled magnet consisting of RE-123 coils and an iron return yoke in its cryostat was tested on the beam line of the Heavy Ion Medial Accelerator in Chiba (HIMAC). The magnet has a room temperature beam duct, at which a magnetic field of 2.4 T is generated, whereas the maximum magnetic field to which coated conductors are exposed is approximately 4 T. On the beam line of the HIMAC, at first, beam guiding using the magnet was demonstrated, and then a carbon-ion beam was injected intentionally into the RE-123 coils of the magnet to simulate the incident of uncontrolled beam injection into accelerator magnets. Repeated excitation experiments of the magnet were conducted in order to study its tolerance against AC loss and stability, as well as the reproducibility of the magnetic field generated. The magnet was excited repeatedly with a saw-tooth waveform to examine the tolerance against AC loss. Next, we examined the influence of shielding current on the field stability and reproducibility at the steps during ramping down, where the current was held constant. Prior to such series of tests using the magnet, the feasibility of quench detection using voltage taps and protection using a dump resistor were studied through quench experiments using short pieces of RE-123 coated conductors. Indeed, such quench detection and quench protection schemes were implemented for the test magnet.