Stability of superconducting coils made of NbTi wires internally doped with large heat capacity Gd2O3 powder

Abstract

During the past decade we have been carrying out R&D aimed at increasing the stability of low temperature superconducting magnets. The main idea is to enhance the superconductor temperature margin by means of introduction into the winding of several volume per cent of specific substances with enormously large heat capacities (LHCS) at liquid helium temperatures. Two doping techniques have been developed at the Kurchatov and Bochvar institutes: the ‘external’ one—introduction of a dopant into the epoxy compound—and the ‘internal’ one—the introduction of doping filaments directly into NbTi and Nb3Sn wires. Up to now, our experiments with LHCS internal doping have been carried out on short samples only. In this paper we report the first experimental and numerical investigation of the stability of small-scale internally doped coils made of NbTi wires of a new type, with Gd2O3 ceramic filaments. The coil wound from doped wire and an identical control coil without any doping were subjected to electromagnetic pulses with 1.4–7.4 ms duration. Minimum quench energies for the doped coil turned out to be about 80% larger than those for the undoped one. The gain is especially pronounced in the range of large transport currents (∼0.9Ic). Comparative effectiveness analyses of the two (external and internal) LHCS doping techniques are also presented.