Liquid Helium-free Superconducting Magnets

Abstract

A liquid helium-free superconducting magnet was realized using high-temperature superconducting current leads as the practical application after the discovery of high-temperature superconductors. A tiny cryocooler with a small refrigeration capacity was successfully linked with a superconducting magnet employing conventional superconducting wires. This results in getting rid of liquid helium from the inevitable condition for a magnet operation. Although the high-field properties at low temperatures below 2.2K for NbTi alloy and Nb₃Sn compound superconducting wires have been concentrated on so far, the superconducting properties at high temperatures above 4.2K become rather important now, and the operating temperature from 5 to 6K is adopted as typical coil temperature. Since the liquid helium-free superconducting magnet works in a vacuum, cryogenic stability and quench protection based on a superconducting magnet immersed in liquid helium have to be reconsidered. In the near future, a liquid helium-free superconducting magnet wound with conventional low-temperature superconductors as well as high-temperature superconductors will make rapid progress, and high-field applications will be outstandingly enlarged. This article describes several key technologies for liquid helium-free superconducting magnets.