Dependence of quench current level on current ramp rate in AC superconducting windings under different fixing conditions

Mechanical instabilities in AC Nb-Ti superconducting wire are theoretically investigated. We derived the expressions for the temperature rise of the SC wire due to the friction between the wire and the bobbin to estimate the quench current degradation induced by mechanical disturbances. The quench current levels were calculated for different conditions of frictional force and current ramp rate. It is confirmed that a certain frictional force brings about the lowest quench current level. It is also found that the quench current degradation induced by mechanical disturbance may not occur when the current increases rapidly.