ACOUSTIC-EMISSION FROM SUPERCONDUCTING MAGNETS - THE DIFFERENCE BETWEEN LAYER WOUND COILS AND PANCAKE WOUND COILS

The energy counting rate of acoustic emission (AE) is measured as a function of energizing current for several simple-shaped unimpregnated superconducting magnets. A simple theory based on the frictional motion of the conductor predicts that the AE rate increases monotonically with increasing current. This is confirmed by experimentation using test coils. The practical magnets, however, exhibit a different behavior. For layer wound coils, the AE rate has a peak in the high current region when the current increases. For pancake wound coils, the AE rate has a peak in the low current region.