Free Expansion of an Isolated Plasma Column

Abstract

An isolated column of plasma is formed by the partial ionization of neutral argon gas with an intense, high‐energy photon beam. The manner in which this plasma expands radially from its initial prescribed position is observed in a region where the plasma has no interaction with confining walls. It is shown that the expansion proceeds initially in accord with the wave equation, having a velocity of propagation u ≈ (γkT_e/M_i)^1/2, a value predicted theoretically by Shimony and Cahn. The driving force for the plasma expansion comes from the electrons, which are in turn cooled predominately by the adiabatic expansion.