Quench onset and propagation in Cu-stabilized multifilament MgB₂ conductors

The quench development of Cu-stabilized metal-sheathed MgB₂ conductors has been analysed. Experimentally, energy pulses were deposited into the conductor by passing rectangular current pulses through a graphite-based epoxy heater. The temperature and the electric field profiles around the point heat disturbance that gives rise to a quench, as well as their time evolution, were measured from multiple voltage taps and thermocouples along the conductor. The measurements have been done at self-field under two different conditions: in vacuum and in Ne vapour. The experimental results are in qualitative agreement with the simulated ones, obtained by solving the one-dimensional heat balance equation of the system and using a finite n value characterizing the I–V curves (V∝Iⁿ). The temperature and current dependences of the minimum quench energy and the quench propagation velocity are presented. Our results show that the nonlinear power-law current sharing in the normal zone had significant influence on the onset of the quench process and resulted in a marked deviation from the classical quench theory based on the critical state model.