The arcing behaviour of a number of refractory metals and graphite has been examined by negatively biasing specimen electrodes in the presence of a pulsed rf discharge. The main object of this work was to select anode materials for gas-filled valves which would reduce their tendency to arc-back under severe Commutation conditions.The voltage at which about 5 % of the pulses resulted in an arc, at an argon ion current density of 1.2 kA m-2, was used as a figure of merit. Of the materials examined, tungsten was the best with a figure of merit of 15 kV and graphite the worst with 6 kV.A good correlation was obtained between the results and the published values for the vacuum arc voltages.

No abstract

No abstract

This paper describes the characteristics and potential uses for plasma chemistry of the sac which occurs at a constriction in a dc glow discharge (SESER). It is found that the rate at which molecules are dissociated is increased in the presence of a plasma sac; in the sac itself the dissociation rate per unit volume can be three orders of magnitude greater than in the positive column. Plasma sacs have been produced in an ammonia discharge with currents in the range 50 to 600 mA, pressures between 0·02 and 2·0 Torr and flow rates of 0·1 to 14 mg s−1, the direction of flow being through the plasma sac from anode to cathode. The dissociation of ammonia to hydrogen and nitrogen has been measured with a mass spectrometer. Optical spectra show that the intensity of all lines is higher in the plasma sac than in the positive column; hydrogen lines, Hα and Hβ are seen in the sac but not in any other region of the discharge. Strong NH lines are seen but none from NH2 and it is concluded that excited NH radicals may play an important role in the dissociation process. The high dissociation rates and intense spectra appear to be caused by the high-energy electrons in the plasma sac. A constriction in a gas discharge (SESER) appears to have interesting potentialities for plasma chemistry.

No abstract