The classical electron-ion collision rate, ${\nu }_{\mathrm{ei}}$, has been deduced in the absence of Ohmic heating from the inverse bremsstrahlung absorption rate measured on a laboratory plasma subjected to an intense microwave electric field $E$ whose frequency $\omega$ is near the electron plasma frequency ${\omega }_p$. The observations, carried out in the transition range, where $\frac{\mathrm{eE}}{\left(m\omega \right)}\approx {\left(\frac{k{T}_e}{m}\right)}^{\frac{1}{2}}$, yield a simple empirical relation that describes the decrease of ${\nu }_{\mathrm{ei}}$ with increasing $E$.

• Received 26 August 1974

DOI:https://doi.org/10.1103/PhysRevLett.33.1210