Reproducibility of a titanium plasma vacuum spark discharge

Abstract

The results of an extensive operation of a vacuum spark plasma using Titanium electrodes in a 120-ns 150-kA discharge are presented. The hot spots are found to form with a regular spacing in a zippering Z-pinch plasma, which forms close to the cathode and extends to approximately two thirds of the anode separation over a period of a few nanoseconds. The axis of the discharge is well defined by an initial plasma from a Nd:YAG laser focussed onto the cathode electrode surface. The statistics of the formation of the hot spots are given for the life of one anode electrode. Between one and three hot spots form and the favored positions are at 1.5 and 3.0 mm from the cathode and the strongest emission, as observed in a filtered X-ray pinhole camera, comes from the hot spot closest to the cathode. The emission spectra resolved between 5 and 35 nm shows a wide range of Ti ionization which allows the temperatures of the anode blow off plasma, the Z-pinch and the hot spot plasma to be distinguished. These results are compared with filtered PIN diode signals and filtered pinhole images. The emission spectrum and the statistics of the axial localization of the hot spots are discussed in the context of potential applications to extreme-ultraviolet lithography.