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K: Fachverband Kurzzeitphysik

K 11: Poster

K 11.1: Poster

Tuesday, March 31, 2009, 17:30–19:30, Foyer des IfP

Time-resolved Spectroscopy on Cathode Spots of a Vacuum Discharge — •Ralf Methling¹, Dirk Uhrlandt¹, Sergey Popov², Alexander Batrakov², and Klaus-Dieter Weltmann¹ — ¹INP Greifswald, Felix-Hausdorff-Str. 2, D-17489 Greifswald — ²Institute of High-Current Electronics SB RAS, Tomsk, Russia

Cathode spots show a very dynamic behaviour. In the last one or two decades, our knowledge on vacuum spots could be remarkably enlarged due to the great improvements in experimental techniques, e.g. by the application of fast intensified CCD cameras. Two-dimensional imaging techniques with high time resolution yielded a wealth of new information on the spot (sub-) structures, their dynamics and lifetimes. Ultra-high time resolution in the sub-ns range with long measuring intervals was obtained with one dimensional streak imaging.

Our goal is to investigate the spectral dynamics of the optical emission of the cathode spots. Therefore, a 0.5 m spectrograph was combined with a streak camera. Limits concerning wavelength and time resolution as well as the emission intensity will be discussed.

The experiments were carried out under UHV conditions using a liquid metal cathode of GaIn alloy. We present first results in which spectral lines of the atom and single as well as double charged ions of the cathode spot plasma could be observed simultaneously. At the beginning of the discharge, the emission spectra are dominated by ionic lines. With a delay in the range of hundreds of nanoseconds atomic lines appear. The intensity of atomic lines is much higher than that of the ionic ones and increases the brightness of the spot in this stage.