Millimetre-wave diagnostics of a pinched linear discharge

Experiments were carried out using 8.9 and 4.3 mm radiation to explore the properties of a pinched discharge between plane electrodes. The discharge had a maximum energy of 10kJ at 10kV and took place in argon at pressures of 75 and 300¿m Hg. Millimetre-wave radiation was directed on to the discharge tube normal to its axis, and the transmitted and reflected signals were recorded. Analysis of these records gave detailed information about the times of certain changes in the plasma, not only during the afterglow but also during the much shorter period of current flow when pinching, if any, occurred. Observations were, in general, found to be independent of the shape of the incident beam, but were critically dependent on the gas pressure and therefore on the flow rate and the discharge-repetition frequency. Other measurements-of voltage, current and luminosity-were used as required to augment and compare with the millimetre-wave results: where comparison could be made, the agreement was good.