A magnetic field generator, a persistent current switch assembly for such a magnetic field generator, and the method of controlling such a magnetic field generator

摘要

A magnetic field generator has a superconductive coil (1) immersed in a coolant material (6). When power is supplied to the superconductive coil (1) from a suitable power source (5), the superconductive coil (1) is energised to generate the magnetic field. The ends of the superconductive coil (1) may then be shorted through a persistent current switch (2), to maintain the magnetic field without the need for further power. The persistent current switch (2) has a superconductive connection (12) connected across the ends of the superconductive coil (1) and a heater (13). These components are enclosed in a casing (15) with a gap (14) between these components and the casing (15). Apertures (16) in the casing (15) permit coolant material (6) to enter the gap (14). When the heater (13) is energised, it heats the coolant material (6) in the gap (14) until it vaporises. There is then a significant decrease in the thermal conductivity through the gap (14) hence the superconductive connection (12) is heated rapidly to its critical temperature. Only low power is needed. When the heater (13) stops being energised, liquid coolant material (6) fills the gap (14) thereby rapidly cooling the superconductive connection (12) to below its critical temperature. IMAGE