High voltage breakdown measurements of a large area SMES-ETM mockup in gaseous helium and air

Breakdown voltage measurements of a SMES-ETM (superconducting magnet energy storage-engineering test model) mockup are presented for gaseous helium and air at room temperature. The mockup dimensions are 1.35 m long by 0.15 m high. Four critical configurations are simulated (layer-to-layer, dewar-to-layer, coil-to-dewar and turn-to-turn) under four pressure conditions (0.25, 0.5, 0.75 and 1.0 atmospheres). The experimental results for the first three configurations are in rough accord with published data of breakdown voltages in air and helium (Paschen curve). The thin G-10 insulation layer of the fourth configuration provides an excellent insulation capability. Experimental breakdown voltages are compared to worst-case design specifications at one atmosphere. All worst-case safety factors exceed 10. The results indicate that design voltage specifications are adequate for operation in a worst-case quench scenario at one atmosphere helium.<>