On the saturation luminance of high density microsecond arc channels

The emission of high current microsecond arc channels in argon and helium, with a 1-mm gap is studied by means of a 20-nsec exposure Kerr cell shutter, and profiles of the relative luminance B are determined from the photographic arc image. This method is largely unaffected by instabilities in the arc position; the scatter of relative luminance values was smaller than +/- 5%. Maximum values of the saturation luminance B in the axis of the arc channel are observed over a wide range of arc current which is altered by the gas pressure. A ratio of B(He)/B(A) = 1.52 for the two gases is determined. The luminance profile across the arc channel demonstrates increasing opacity after saturation is reached.