A Novel Thermal Insulation Method for a Next-Generation Conduction — Cooled Superconducting Magnet
We have developed a new thermal insulation method for use with superconducting magnets or in applications where temperature needs to be maintained within a limit. Termed as Multi-shell-insulation (MSI) method, this method uses several thermal-energy storage shields to intercept heat flowing into the superconducting magnet. The shields are arranged in a vacuum vessel so that each shield is inside another slightly bigger shield and the superconducting magnet is inside the innermost shield. To use MSI, the shields are first cooled to about the same temperature as the superconducting magnet and then they are thermally separated from the cooling means. The temperature of the outermost shield would rapidly rise, but those of inner shields would rise only slowly; the closer the shield to the center, the slower the temperature rise. To demonstrate MSI effect, we used 10 copper shields, five of which were cooled to 30K and the other five to 4K by a two-stage Gifford-McMahon refrigerator. The 3kg-innermost shield could be maintained below 30K for a one-month period: a promising result for the realization of a cryocooler-detached, high-Tc superconducting magnet. It was also possible to maintain the inner shield below 10K for 8 days by coating the three inner copper shields with HoCu2 and Er3Ni.