HIGH-SPEED IMAGING OF THE PULSED-FIELD FLASHOVER OF AN ALUMINA CERAMIC IN VACUUM

An intensified high-speed imaging technique was used to observe the optical events associated with the pulsed-field breakdown of an alumina ceramic tube having two concentric planar electrodes metalized onto its end face. HV pulses, typically of 5 kV amplitude (5 kV mu s(-1) rate of rise), were applied to the radial M-I-M insulator-electrode regime under ultrahigh vacuum (pressure < 5x10(-7) Pa), with video recordings made at 1000 frames per second. Images of the observed breakdown phenomena are presented, viewed both along the center axis and also in the plane of the M-I-M structure. These breakdown images are discussed in relation to plasma jets associated with vacuum arcs and, in particular, on the nature of the ion species within such jets.