Influence of high heat capacity substances doping on quench currents of fast ramped superconducting oval windings

摘要

The effect of high heat capacity substances doping on superconducting magnets ramp rate induced quench currents has been investigated for three oval windings. The windings were wound from Rutherford type cable (1.44 x 4.64 mm~2), made of 10 multifilamentary NbTi strands 0.85 mm dia. Before application of electrical insulation and winding the cable was covered with epoxy resin with three different fillers: BN (boron nitride-a standard filler for preventing of epoxy cracking at low temperatures), and two rare-earth interme-tallic compounds (HoCu_2 and CeCu_6). The specific heat of these compounds at liquid helium temperatures is extremely high. The volumetric fraction of these compounds was 2.9 percent of the total winding volume, corresponding to 4.5 times increase of averaged winding heat capacity for HoCu_2 and to 1.5 times increase for CeCu_6. At high ramp rates (~4 kA/s, or ~6.5 T/s) quench current of HoCu2 doped winding was 35 percent higher than that for the BN doped one, while for CeCu_6 doped winding the quench current increase was 12 percent . Measured quench currents match values calculated with our theoretical model, in which whole doping substances enthalphy was taking into account. It indicates that the enhanced enthalphy is fully utilized in the used range of dB/dt.