Dynamics of the pulsed high-current vacuum arc in semiuniform electrode geometry

A vacuum spark develops in the metallic vapor emitted by the electrodes. The plasma thus created experiences contractions and expansions and emits X-rays. We report an investigation into the initial dynamics of the arc. A fast 1-kJ generator was used for the experiments. The diagnostics employed include optical frame and streak photography, time-resolved filtered X-ray detection, and pinhole X-ray photography. The results obtained indicate that there is plasma column pinching, some of it producing X-radiation. The energy of the X-rays tends to be rather soft and seldom were characteristic lines detected, even when exchanging electrodes, which are made of dissimilar material. This demonstrates that radiative collapse is not attained at this level of energy and that from the point of view of X-ray emission, it is irrelevant what metallic vapors initiate the vacuum arc.