Magnetic and collisional effect of presheaths

Abstract

The effects of both magnetic field and collisions on presheath properties are experimentally investigated in plasmas with electron temperatures much greater than ion temperatures. Measurements of plasma potential in collisionless plasmas show presheath thicknesses at boundaries oblique to magnetic field to be approximately (C-s/omega(ci))sin psi where C-s is the ion sound speed, omega(ci) is the ion gyrofrequency, and Psi is the angle between the magnetic field and the normal to the wall boundary. Measurements of plasma potential in collisional plasmas find presheaths consisting of two distinctive regions. With ion-neutral collision mean-free path lambda(n)<(C-s/omega(ci))sin psi the presheath region next to the sheath has collisional characteristics and a thickness of approximately (0.5-0.6)lambda(n). The corresponding presheath region adjacent to the bulk plasma has magnetic characteristics and a thickness of approximately (0.5-0.9)(C-s/omega(ci)sin psi. Equipotential contours in the collisional region of this presheath are found to be parallel to the boundary, while those in the magnetic region are not. (C) 1995 American Institute of Physics.