Diffusion Cooling of Electrons in Ionized Gases

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Abstract
The term "diffusion cooling" is used to describe the situation in which the average energy of an electron swarm is reduced by the diffusion of the faster electrons to the container walls. In the present experiment, measurements of the ambipolar diffusion loss of electrons during the afterglow reveal the presence of diffusion cooling by the reduction in the ambipolar diffusion coefficient. In low-pressure neon and argon afterglows the "thermal contact" between electrons and gas atoms is poor; consequently the diffusion loss of the fast electrons causes a large reduction in electron "temperature" with respect to the gas temperature. When small amounts of helium are added, the thermal contact is greatly improved, and therefore the electrons are restored to thermal equilibrium with the gas. These experimental observations confirm the predictions of a qualitative theory given for the process.