Key issues for application of SUS316 steel to large scale superconducting magnet system

Abstract

The most important behavior of SUS316 in a cryogenic service is serrated deformation after yielding. So-called serration generally happens under stroke rate or cross head speed control during a tensile test. The serration is caused by the adiabatic deformation due to very low thermal conductivity at cryogenic temperature. The large superconducting magnet system in the fusion device requires stiff structure to support the huge electro-magnetic force, and SUS 316 is a common structural material for cryogenic support structure because of non-magnetism, high-toughness, and good machinability and weldability. Since the electro-magnetic force would not decrease so quickly, the serrated deformation has a potential to cause the continuous heat generation and crack propagation which leads to catastrophic failure of the structure. In this report, some key issues on application of SUS316 stainless steel to the cryogenic support structure of a large superconducting magnet system will be presented and pillar-wall structure for the support structure will be discussed conceptually.