Metal vapor densities and excitation temperatures in a pseudospark switch

The densities of iron, tungsten, copper, and nickel vapors produced by pseudosparks in a switch-like configuration are measured by laser-induced fluorescence. The cathode is made of a composite material essentially consisting of tungsten, but also containing the other metals mentioned. Total vapor densities are calculated from ground state densities using the excitation temperature of iron, which decays from 1900 K at 9 μs after initiation of the discharge to 600 K about 150 μs later. With maximum copper and tungsten vapor densities of 1.5×10¹⁸ m^-3 and 2×10¹⁷ m ^-3, respectively, the composition of metal vapor differs considerably from that of the cathode material. Iron and nickel vapors are present with densities in the range of 10¹⁶ m^-3. By comparison of vapor density ratios with vapor pressure ratios it is found that regions with temperatures in excess of 5000 K exist on the cathode. These are attributable to emission sites providing the electrons for current conduction. The vapor densities are roughly proportional to the current amplitude, while the gas pressure has practically no influence between 15 and 30 Pa