Interferometric measurement of the electron density in a pseudospark switch

Summary form only given. In the recent years pseudospark switches have been developed for several applications in pulsed power devices. The pseudospark is a low pressure gas discharge usable as a closing switch. For medium power (I<30 kA, pulse length<500 ns) sealed-off devices are available for tests. In the high current regime (currents>30 kA up to a few 100 kA, pulse length<20 /spl mu/s) only devices connected to a vacuum system are in use. The pseudospark transforms from a special hollow cathode discharge to a metal vapour arc like discharge type when the current exceeds 35 kA. Fast shutter photographs of the discharge prove the appearance of filaments at currents exceeding 40 kA corresponding to a dip in the forward voltage drop and a rise of the erosion rate of about one order of magnitude (4 to 40 /spl mu/g/C) for molybdenum electrodes. The knowledge of the electron density distribution provides more information about these phenomena The discharge is no more radial symmetric to the central apertures at these high currents. A contraction to a small area on the plane electrode surface takes place. Therefore a tomographic setup is necessary to measure the electron density distribution with interferometry. To eliminate the contribution of the ions and the neutral plasma particles to the phase shifts two wavelengths are necessary.