Development of the turn releasing technology for the Nb₃Sn pancake coil of CFETR CSMC

A central solenoid model coil (CSMC) is being developed to verify the large-scalar superconducting coil manufacture technology for China Fusion Engineering Test Reactor (CFETR) in Institute of Plasma Physics, Chinese Academy of Sciences (ASIPP). The turn insulation wrapping of the Nb3Sn pancake coil is conducted after the coil heat treatment. The turn releasing technology is necessary to be developed and verified to insure there is no damage to Nb3Sn conductor during the turn insulation wrapping of the Nb3Sn pancake coil. This paper introduces the design, analysis and verification for the safe stretch distance, the design and debugging of the special equipment, and the process experiment with the 4 × 4 mockup coil.