Quench time lag of NbTi mechanical PCS with ramped current waveforms Original Research Article

This paper describes characteristics and generation mechanism of quench time lag of NbTi mechanical persist current switch (PCS). The quench time lag tD was defined as a time delay between quench occurrence and the moment of the instantaneous value of the switch current exceeding a static quench current of the PCS. Quench time lag characteristics were investigated by using ramp current waveforms in order to clarify effects of the current sweep rate. It was found that the quench time lag decreased with increasing current sweep rate. A theoretical model was proposed in order to clarify the quench mechanism with a transient current waveform. In the model, the quench time lag was calculated by computing temperature rise of a superconducting connection bridge due to an AC loss and a flux flow loss. The simulation results of the quench time lag were in a good agreement with experimental data when cooling effects of liquid helium were taken into account.