The expansion of pure electron plasmas due to collisions with background neutral gas atoms in the Electron Diffusion Gauge experiment device is observed. Measurements of plasma expansion with the new, phosphor‐screen density diagnostic suggest that the expansion rates measured previously were observed during the plasma’s relaxation to thermal quasi‐equilibrium, making it even more remarkable that they scale classically with pressure. Measurements of the on‐axis, parallel plasma temperature evolution support the conclusion. © 2003 American Institute of Physics