Drift Velocity of Electrons in Helium

Abstract

The drift velocity of electrons in helium at 300°K has been measured for E/p values between 4X10" 4 and 40 volt/cm-mm Hg. The data for E/p < 1 volt/cm-mm Hg were obtained from measurements of electron transit time in a modernized version of the double shutter tube developed by Bradbury and Nielsen. The data at high E/p were obtained from microwave measurements of the electron density in a positive column of a low-pressure discharge. The measured drift velocities are in good agreement with previous results in the E/p range from 10" 1 to 3 volt/cm-mm Hg. At E/p less than 3X10~3 volt/cm-mm Hg the electrons are essentially in thermal equilibrium with the gas. Margenau's theoretical expression for the drift velocity of electrons in a gas for which the cross section for momentum transfer is independent of electron energy is found to fit the data for E/p < 1 volt/cm-mm Hg to the accuracy of measurements. The cross section which gives the best fit of the theory to the data is 6X10 -16 cm 2 .

Theory of Gas Discharge Plasma

“…Summing up these integrations, we obtain for the flux of resonant photons from the surface of a cylinder uniform plasma [258,259] …”

Possibility of locking of stimulated Raman emission components in an optical resonator with a dispersive medium

“…It is now well known that there are a large number of possible secondary ionization processes in helium (Phelps 1960, Davidson 1962. It is of interest to consider whether any information can be obtained about the predominant secondary ionization process in helium at high pressures from the results given in the previous section and from the previously reported (I) variation of ,/a with E/p,.…”

“…The following data w e used in the computation of elastic losses: Townsend's (1947) experimental values of E? the mean electron energy, and Townsend and Bailey's (1923) values of A, the fraction of the mean electron energy lost per elastic collision; values for the total elastic cross section Qe were taken from Phelps, Fundingsland and Brown (1951) and values of the electron drift velocity Wfrom Phelps, Pack and Frost (1960). The ionization (Ci) and elastic ( e e ) losses were thus computed and equation (2) It is clear from the table that about 707; of the energy loss in this region is due to excitation and this, together with the experimentally observed variation of ,/a with E/p,, W i W s that the predominant processes of secondaiy ionization in helium at high pressure arise from the production of excited states.…”

Electron Mobility Transition in a Random System of Hard-Core Scatterers

“…14 The electron transport has been investigated by Levine and Sanders 15 using time-of-flight techniques at temperatures near 4°K and densities of the order of 10 21 atoms/cm 3 with results as shown in Fig. 2.…”