Thermal Performance of the LDX Floating Coil

Abstract

The Levitated Dipole Experiment (LDX) is an innovative facility to study plasma confinement in a dipole magnetic field, created by a superconducting solenoid (floating coil), which is magnetically levitated in the center of a 5 m diameter by 3 m tall vacuum chamber. The floating coil (F‐coil) consists of a Nb3Sn magnet installed inside a strong vessel filled with high‐pressure helium gas at room temperature. It is surrounded by a fiberglass‐lead composite radiation shield and by a toroidal vacuum shell. The cryostat design provides the ability to operate the magnet for several hours of wanning while suspended in the middle of the vacuum chamber without electric and cryogenic connections to the coil. For this reason the magnet is charged/discharged inductively in a lower part of the vacuum chamber. The retractable cryogenic transfer lines serve to cool down the magnet to 4.5 K before it is lifted to the operating position. The F‐coil can be re‐cooled multiple times while maintaining its field and current. This paper describes the thermal performance of the F‐coil.