Normal zone origination and propagation in superconducting wire with fast changing current

The key to understanding the fast quench phenomenon in multistrand cables is the normal zone origination and propagation in superconducting wires with fast changing currents. Results of experiments simulating the situation in strands during fast quench development are presented. The maximum quench current, normal zone velocity, increase of current and time before quench are measured in NbTi-CuNi composite wire at different transport current ramp rates and at different initial currents. Normal zone velocity propagation depends on I(t) and I˙(t) only. The presence of an initial current leads to the acceleration of normal zone propagation at decreasing current. The initial current also leads to a reduction of the current increase and the time when a quench starts. We use the results received to explain the appearance of fast quench phenomenon in superconducting cables with insulated or highly resistive matrix strands