Collector Measurements in the Positive Column of the Glow Discharge in Neon, Argon and Helium

The LANGMUIR method for the use of sounding electrodes in low pressures discharges, has been applied for a study of the positive column in Ne, Ar and He. The electrons are found to have a Maxwellian distribution of velocities, with an average velocity as high as 11v, the equivalent temperature increasing with decreasing pressure. It is suggested that the wall plays an important part in the realization of the random velocity distribution; qualitatively, secondary effects in the sheath on the wall can account for the presence of LANGMUIR’s fast electrons. The positive ion currents do not show saturation with increasing accelerating voltage on the collector, and the calculated values from the space charge equations come out 50% of the measured ones. This cannot be accounted for by a disturbing effect due to the collector. The increase is probably caused by an electron emission from the metal with subsequent impact ionization in the sheath, the secondary electrons being liberated by positive ion impact on the metal. Different other possibilities are also discussed. A general discussion of this type of discharges at very low pressures is given.