The expansion of plasma in the early stage of an inductive high frequency discharge in helium has been investigated experimentally. In a collision dominated case a non-stationary ambipolar diffusion current transfers a lightly ionized plasma from a source region into an initially neutral ambient gas. Time resolved measurements of electron density and electron temperature have been performed at the source and at a test point outside of the plasma source region by 4 mm-microwave interferometer and pulsed double probe techniques. A comparison of experimental data with calculations based on a simplified diffusion model for collision dominated plasma expansion is given. © 1969 Springer-Verlag.
