NORMAL ZONE ORIGINATION AND PROPAGATION IN SUPERCONDUCTING WIRE WITH FAST CHANGING CURRENT

The key to understanding the fast quench phenomenon in multistrand cab les is the normal zone origination and propagation in superconducting wires with fast changing currents. Results of experiments simulating t he 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 d ifferent transport current ramp rates and at different initial current s. Normal zone velocity propagation depends on I(t) and I(t) only. The presence of an initial current leads to the acceleration of normal zo ne propagation at decreasing current. The initial current also leads t o a reduction of the current increase and the time when a quench start s. We use the results received to explain the appearance of fast quenc h phenomenon in superconducting cables with insulated or highly resist ive matrix strands.