In this paper we report our recent research on thermal stabilization of low-temperature superconducting magnets by means of large heat capacity substances (LHCS). Two samples (lengths ∼100 m) of NbTi composite wires with additional internal filaments made from intermetallic compound PrB6 (5.9–7.3 vol.%) were produced and tested. The design of the wires was similar to that of the conventional MRI sc wires, except for their smaller diameter (0.835 mm instead of 1.345 mm). Our final goal was the investigation of the possibility to minimize (or even eliminate completely) the necessity of MRI magnets training before their commissioning. The comparative stability measurements showed a twofold increase of the minimum quench energies (MQEs) of the doped wires against short heat disturbances. The magnetic field corresponding to the first flux jump increased by 50%. In MQE tests, the PrB6 heat capacity was fully utilized over the course of a 1 ms heat pulse. In the thermomagnetic stability measurements, the efficiency of LHCS doping was about 75% due to the fast evolution of the flux jumps.

Several years ago at Kurchatov Institute the R&D program on the new type of superconducting magnets (SM) doped with large heat capacity substances (LHCS) in order to improve their stability was started. We began from an "external" doping by the LHCS powder mixed with epoxy resin using the wet-winding process. Later on at Bochvar Institute the methods to introduce LHCS inside superconducting wires (both NbTi and Nb3Sn based) were developed. The comparative tests of LHCS doped wires and model windings with LHCS have shown positive results regarding a considerable increase of critical energies, improving of thermomagnetic stability and training behavior. The state-of-the-art of these methods is reviewed and their perspectives are discussed. (C) 2011 Elsevier Ltd. All rights reserved.

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.

Two samples of Nb3Sn multifilamentary wires 0.82 mm diameter were prepared by the bronze method. One of the samples was internally doped with 7 vol% of PrB6, a large heat capacity substance (LHCS), while the other sample did not contain any LHCS and was used for comparison. The influence of LHCS internal doping on the stability toward short (similar to 1 ms) heat disturbances and critical currents in a transverse external magnetic field up to 3 T was investigated both experimentally and computationally. The average heat capacity for the doped sample in the temperature range 4-10 K was three times larger than for the undoped one. For the LHCS-doped sample its critical current was found to be slightly larger than for the comparison sample (6-8% depending on the external field), while its critical energies towards external heat disturbances were five times larger.