Low Voltage Discharges in Helium

Discharge through helium,.01 to 2.9 mm pressure.—A hot filament cathode and disk anode were mounted in a glass frame 10 to 12 cm apart, the frame being so arranged that it could be moved magnetically inside a glass tube of diameter about 4 cm, with reference to a fixed exploring electrode. Measurements of potential distribution and of mean energy and concentration of electrons were made at three pressures,.095, 0.5 and 2.9 mm. Although precautions were taken to secure pure He, striations were obtained because of a trace of neon. The results are similar to those obtained by Bramley for ${\mathrm{hydrogen}.\mathrm{}}^1$ The mean electron energy decreases to a minimum beyond the negative glow, then rises to a maximum beyond the face of the first striation. The electron concentration falls from a maximum in the negative glow to a minimum near the cathode side of the first striation; within the limits of accuracy of the work, it increases in a given region of the discharge with an increase of pressure and is proportional to the current density of the discharge at a given pressure. Calculations of the positive ion concentrations by Langmuir's formula and also by one developed by McCurdy, give results which seem to be equal to the electron concentrations, but as both methods are merely approximations, this result is not very reliable.