Investigation of the interaction of dense noble gas plasmas with cold cathodes: I—Experimental setup and application to Al, Cu, Ti, and graphite cathodes

Abstract

AbstractThe formation of arc spots on cold cathodes, called arcing, is an interference factor in all kinds of plasma technical devices. It is investigated by igniting an arc in a clean atmospheric pressure Ar or Kr filling of a stainless steel vessel. It is brought into interaction by a magnetic blast field with a negatively biased commutation electrode (CE), formed by a rod with a diameter of 2 mm consisting of pure Al, Cu, Ti, or graphite; its end face is polished with diamond grinding powder. The arc commutation is observed by short‐time photography, streak camera records, and temporally highly resolved optical spectroscopy for different applied voltages. The emission of ion lines of the filling gas and of vaporized electrode material by the plasma in front of the cathode is indicating the formation of a positive space charge layer in front of its surface. It provides the ions, which induce secondary electron emission of the cathode surface and with it, the arc commutation. The commutation time tc elapsing between a signal generated by the arc plasma in front of the CE and the beginning of a current flow through the electrode increases for low voltages with increasing permittivity of a surface layer formed by electrically insulating metal oxide and decreases with increasing electrical conductivity of the layer. It is lowest for graphite without an oxide layer. On scanning electron microscope pictures, taken of the end face of the electrode after arc commutation, craters with diameters of less than 1 μm are visible.