Striated Discharge in Hydrogen

Abstract

Potential distribution, electron concentration and mean electron energy at eleven points were determined for a discharge through a tube 15 cm long at pressures of.625,.20,.90 and.02 mm, using Langmuir's probe method. The total potential difference was 270-300 volts. The potential dropped to a minimum within 2 mm of the cathode, of 125, 60 and 20 volts for pressures.20,.09 and.02 respectively, giving a reverse gradient in a region 1 to 2 cm long through which the current must have been carried by diffusion of positive ions and electrons. The gradient was also reversed at the anode edge of a striation for pressures of.20 and.09 mm—the lower pressure.02 mm gave a uniform positive column. The electron concentration reached a maximum 1 to 2 cm in front of the cathode; the values, in general, are lower the higher the pressure. The mean electron energy decreases sharply at the cathode to a minimum of 1 to 2 volts, then rises gradually to about 10 volts at the beginning of the positive column; it also reaches 10 volts at a striation. Such electrons have sufficient energy to cause the ionization which is associated with the luminosity in the positive column. The anode drop within 2 mm was only 5 to 15 volts, the potential distribution depending on the position of the nearest striation.