Abstract
Metal ions generated from an impulse vacuum arc were measured by a time of flight (TOF) method. A gap between a needle cathode and a rod anode, a grid electrode made of metal mesh, a linac tube and an ion collector electrode were installed in a vacuum chamber and the gap was fired by a negative sinusoidal arc current. A negative square pulse was applied to the linac tube at an appropriate time after the arc ignition to extract a sample of ions. Pb+ and Pb++ ions were measured for a lead cathode and Cu+, Cu++ and Cu+++ were measured for a copper cathode.
TOF ion currents were measured as a function of the ion extraction time. The duration of the sinusoidal arc was 13 μs and Pb+ ion currents were measured only within 49 μs after the arc ignition, while Cu+, Cu++ and Cu+++ ion currents were measured within 15.5 μs. The lifetime of the ions, i.e. the upper limit of the ion residence time at the space between the grid and the linac tube, was betermined from the time distance between the arc extinction and the critical time of the TOF ion detection. Based on the above definition, the lifetimes of the lead and copper ions obtained were 36 μs and 2.5 μs, respectively.
