An experiment on the plasma expansion into a wake

Abstract
Experiments on the expansion of a plasma into the wake region behind an object inserted in a flowing plasma are described. The dominant expansion mechanism that fills in the wake is determined to be a self‐similar expansion. Accelerated ions with a velocity greater than the local ion‐acoustic velocity are detected ahead of the self‐similar expansion front. In a plasma with two species, two groups of accelerated ions are detected.