Magnetized plasma flow through a small orifice

Deuterium plasma flow through a circular hole in a flat conducting plate is simulated by the two-dimensional object-oriented particle-in-cell code (XOOPIC) [J. P. Verboncoeur, A. B. Langdon, and N. T. Gladd, Comp. Phys. Comm. 87, 199 (1995)]. A constant magnetic field is oriented perpendicular to the plate surface, and parallel to the cylindrical axis of the hole. Charge neutralization on the interior surface of the hole leads to attenuation of the ion current throughput. The attenuation is stronger than would be expected from a finite Larmor radius model, due to acceleration of ions by the self-consistent radial electric field. The current attenuation has been measured by comparing two Langmuir probes that were operated simultaneously under a wide range of plasma conditions in Tore Supra [Equipe Tore Supra, IAEA-CN-64/02-2, International Atomic Energy Agency, Vienna, p. I-41 (1996)]. One probe was exposed directly to the plasma and the other was hidden behind a graphite shield pierced with either 3 or 4 mm diameter holes. Both the ion current attenuation and the floating potential drop are in reasonable agreement with the simulation results. (C) 2001 American Institute of Physics.