Experimental study of diffusive cooling of electrons in a pulsed inductively coupled plasma

Langmuir probe measurements of the temporal behavior of the electron distribution function in a low-pressure inductive discharge are presented. The structure of the measured distribution functions suggests that the loss of high energetic electrons to the wall of the discharge chamber is the main energy loss mechanism. Electron-heavy-particle collisions play only a secondary role for the energy loss. The rapid loss of energetic electrons—while low energy electrons remain confined in the space charge potential field—leads to a fast cooling of the electron distribution function. We also present a simple model to describe the evolution of the mean kinetic energy and plasma potential on the basis of a distribution function that is cutoff at energies above the potential electron energy at the wall.