Effect of object potentials on the wake of a flowing plasma
Abstract
Measurements and calculations have been carried out to determine the structure of electric potential and ion density in the near wake created by the flow of a highMachnumber plasma past a conducting plate biased with respect to the undisturbed plasma. Results are obtained for a molecular nitrogen plasma with ambient electron densities N of the order of 10^{5} cm^{}^{3}, ion temperatures of θ_{i}≂0.025 eV, electron temperatures of θ∼0.3 eV, and plasma flow velocities of V_{0}≂10^{6} cm/s, corresponding to V_{0}/(θ/M)^{1}^{/}^{2}≂11. For highMachnumber flow past an unbiased object, the wake structure is very nearly that predicted for the expansion of an initially uniform plasma halfspace into vacuum; in this case there is a sharply defined ion front moving under the influence of an electric field produced by charge separation between ions and electrons near the front. With bias potential φ_{p} such that qφ_{p}/θ is in the range 1 to 10, a welldefined ion front still exists, but its motion is strongly affected by the imposed potential. This effect can be explained in terms of the impulse received by those ions passing through the sheath region near the plate edge. Twodimensional simulations of the laboratory experiments were performed by using a multiple waterbag technique. The results for both zero and finite ion temperatures are almost noisefree and support the approximate analytical model. The calculated density for 10 θ negative bias on the plate is compared with the measured profile.
 Publication:

Journal of Applied Physics
 Pub Date:
 October 1987
 DOI:
 10.1063/1.339418
 Bibcode:
 1987JAP....62.2675K
 Keywords:

 Collisionless Plasmas;
 Magnetohydrodynamic Flow;
 Plasma Diffusion;
 Plasma Potentials;
 Finite Element Method;
 Plasma Density;
 Wakes;
 Plasma Physics