Fundamental techniques of superfluid cooling of superconducting magnets and electronic apparatuses are exemplified by an AC magnet. Superfluid helium, as a cryogen for magnets, has excellent properties such as superfluidity and super-thermal conductivity. Despite these properties, its heat transport capacity is restricted by narrow cooling channel configurations of a magnet winding and by the critical heat flux for a surface of a superconducting wire. To obtain the maximum heat transport and maximum critical heat flux, the optimum operational temperature should be between 1.8 and 1.9K. Also mentioned is the heat transfer to superfluid helium under transient state, where one can obtain a critical heat flux that is higher than that under the steady state but with a lifetime less than a one millisecond.
