Speaker
Description
YBCO coated conductors are of interest in a number of possible High Energy Physics applications, like e.g. high field solenoids for muon colliders. A new approach in making YBCO magnets has been suggested recently, where the coils are neither insulated nor epoxied. It is believed that in this approach, the coil is much easier to protect, because one a given zone becomes normal, the lack of insulation lets it share its current to the next winding layer down. Essentially, the various coil windings are no longer completely in series once a normal zone forms. In principle, the current can be shared across the whole winding, thus essentially serving both to re-route the current, but also to distribute the energy, as quench heaters would in a normal active protection scheme. In the present work we have measured current sharing, stability, quench and normal zone propagation in such a YBCO pancake coil at 4.2 K in liquid helium bath. The experiments have been done in applied magnetic fields up to 10 T at transport currents of a certain percentage of the coil critical current. The coil winding 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 to measure quench and NZP. Obtained results are compared with our previous measurements on a coil wound using a kapton insulated YBCO tape.