Development of a Test Conduction-Cooled MgB 2 Coil

We are now developing conduction-cooled MgB 2 coils toward the realization of magnets with 1-MJ magnetic energy. We devised a new fabrication method, which is based on the wind and react method. A bobbin in the react process is made of stainless steel. To improve cooling performance, one of the stainless steel flanges of the bobbin is replaced with an oxygen-free copper (OFC) one after the react process. To prevent winding collapse, these flanges consists of several pieces, and these pieces are replaced in sequence. The OFC flange and the coil winding are bonded with epoxy impregnation. To validate this new method, we fabricated a test coil with an inner diameter of 100 mm and a self-inductance of 8.3 mH by using a multistrand MgB 2 wire. We cooled the test coil by a two-stage GM cryocooler and measured its critical current (I c ) at 25 K. The difference between the temperature of the OFC flange and that of the winding surface was within 2 K. The I c was about 263 A, which had been expected to be 275.8 A in accordance with its load line and short-sample measurements. These results support the validity of our fabrication method.