Considerable increase in the thermomagnetic stability of multifilament superconductors internally doped by large-heat-capacity substances

Cu/Nb-Ti MRI wires with improved stability by incorporating filaments of large heat capacity substance PrB6

“…It is well known that the typical dependency B j (dB/dt) for helium cooled sc wires decreases, and for the high ramp rates comes to the plateau corresponding to an adiabatic stability criterion. We have obtained such dependencies in our previous experiments on monofilament superconductors with external doping (LHCS is in the inter-turn volume) [12] as well as on ITER-type superconductors (Nb 3 Sn + 7% PrB 6 ) & (NbTi + 5%Gd 2 O 2 S) with internal doping [8].…”

“…The B j values rapidly increase for ramp rates in the 0.1-0.5 T s −1 range due to the screening of the external magnetic field by the additional current induced in the copper matrix of the samples. It is interesting that for the composite ITER-type wires with internal LHCS doping from our previous papers [8,12], the corresponding threshold value for dB/dt was about 5 T s −1 .…”

“…For instance, we demonstrated 4-6 times stability increase for the ITERtype Nb 3 Sn wire doped with 7% PrB 6 against short (∼1 ms) electromagnetic disturbances [6] and up to 4 times growth for the NbTi wire with 5% Gd 2 O 2 S [7] (in comparison with wires without LHCS doping). The measurements of thermomagnetic stability (in terms of adiabatic stability criterion) had also shown 50% and 10% growth of the magnetic field of the first flux jump for Nb 3 Sn and NbTi wires correspondingly [8].…”

“…In thermomagnetic stability tests we used the experimental technique developed in our previous works [8]. Two singlelayer coils with Pb-Sn soft soldered turns (referred to below as 'the samples') were wound with wire #1 (NbTi + 5.9% PrB 6 ) and with the comparison wire #3 without additives.…”

“…The composite wires twisting should be taken into account. In the external magnetic field increasing at a constant rate, the gradient of the magnetic field over the sample thickness is divided into two almost identical spatially separated magnetic profiles [8]. Flux jump occurs in one of these most likely in the external one where the magnetic field is maximal.…”