ABSTRACT
Different modes of current transfer to hot tungsten cathodes were observed already many years ago [1]. But only just recently the different modes could be related definitely to basic physical laws by a stability analysis of axially symmetric cathodes [2]. A detailed experimental investigation of HID electrodes revealed at least three different modes [3, 4]: a diffuse mode, characterized by a low current density at the cathode surface and a high global cathode temperature, a spot mode, with a spot of high current density and surface temperature at the edge of a cylindrical cathode, and a so called super spot mode of arc attachment with a symmetric, high density current transfer onto a tiny tungsten tip and a low global cathode temperature. To achieve a better understanding of the experimental results which were found at the Bochum model lamp a numerical simulation of modes was performed.
