A Conduction-Cooled REBCO Magnet With a Single-Stage GM Cryocooler and a Stainless Steel Case for Storing the Coil and Covering it From Thermal Radiation

A conduction-cooled REBCO racetrack coil that is stored and impregnated in a stainless steel case is proposed for mechanical reinforcement of the straight parts. Two racetrack coils composed of a stack of four single pancakes wound with two kinds of the REBCO tapes were fabricated and tested using conventional and new advanced conduction cooling systems, respectively. As the latter a more simplified cooling structure for a REBCO coil without the need for a conventional thermal radiation shield is currently under development. One challenge is restricting the flow of heat to the coil when the cryocooler stops due to an unexpected electrical and/or mechanical breakdown. In this research, the stainless steel case was thermally connected to a single-stage GM cryocooler. Most of the heat load was received by the case, and thermal resistance layers were inserted between the case and the coil surface for controlling the flow of heat into the coil. The REBCO coil was cooled indirectly and operated successfully without any degradation and the temperature rise when the cryocooler stopped was evaluated by experiments and calculations.