A solution to the ‘training’ problem in superconducting magnets

Abstract

A major factor in the design of large superconducting magnets is the problem of premature quenching, notably the ‘training’ effect, associated with the use of epoxy resin impregnants. This paper draws attention to the existence of a simple but neglected solution to this problem. A review is given of a series of tests carried out in 1968–1971 which showed that such effects were considerably reduced in the case of solenoid and quadrupole coils impregnated with wax or oil, allowing currents at least 85–90% of the critical value to be achieved consistently and reliably. The tests included a full scale prototype quadrupole (9 cm bore, 40 kG maximum field). A discussion of the mechanical and thermal properties of such coils indicates no reason to doubt their long term reliability, and the adoption of this solution for operational magnets is recommended.