ION-ENERGY MEASUREMENTS IN A DOUBLE PLASMA-DEVICE

It is found that the ion-energy distribution in a quiescent low-pressure argon plasma that is produced in a double plasma device is anisotropic. More ions drift to the mesh separating the two plasmas than away from it. Ions travelling in these two directions have velocity distributions that approach half-Maxwellians with different temperatures for speeds above the mean speed. The mean-free paths for Coulomb and ion-neutral collisions exceed the plasma size, and the plasma-density fluctuation levels delta-n/n less than or similar 2 x 10(-3) in the main body of the plasma are too small to explain the thermalization of the ion energy distribution. However, the larger fluctuation levels with delta-n/n approximately 0.1 that are observed close to the plasma boundaries and at the sheath at the separating mesh may play a role in the thermalization.