Normal zone propagation, protection and quench measurements in a YBCO pancake coil at 77 K and at 4.2 K in magnetic fields up to 10 T

We have measured stability, and normal zone propagation (NZP) in a YBCO pancake coil in liquid nitrogen bath (77.3 K) and in liquid helium bath (4.2 K). The experiments in liquid helium bath at 4.2 K were carried out in applied magnetic fields up to 10 T and at transport currents of a certain percentage of the coil critical current at a given field. The pancake coil was instrumented for voltage and temperature measurements at several places around the winding, such that both radial and azimuthal quench propagation could be measured. A heater was placed on the inner-most part of the winding. Heat pulses of various powers and durations were generated at different coil currents to measure quench and NZP. A protection circuit with a possibility of setting different quench voltage limits was used to protect the coil after quench.This work was supported by the U.S. Department of Energy, Office of Science, Division of High Energy Physics, under Grant DE-SC0011721- Ic of the coil in self-field at 77 K was 48 A which is 45.5 % of the short sample Ic in self-field Spontaneous quenches occurred both at 77 K as well as at 4.2 K Spontaneous quenches were localized in the 1st quadrant of the winding, between 5th and 12th turn Heat pulses generated localized NZ just above the heater both at 77 K as well as at 4.2 K At 77 K and self field MQE = 16.84 J at Icoil = 39.6 A = 0.825Ic coil At 4.2 K and self-field MQE = 33.0064 J at Icoil = 60