Diffusion of Charged Particles Across a Magnetic Field in ``Short Circuiting Geometry''

Abstract

The diffusion of plasma across a uniform magnetic field was studied in an experimental apparatus of variable length. Thus, it was possible to confirm, experimentally, the influence of the end walls upon a plasma of finite length in the direction of the field lines; this influence is called ``short circuiting effect.'' By reducing the pressure from 2 × 10−3 to 5 × 10−5 mm Hg, an instability was found, and the diffusion coefficient reached a maximum. The onset of the instability was investigated as a function of pressure, magnetic field strength, and length of the plasma column. The results are compared with the analysis of Guest and Simon about the onset of an instability (similar to that of Kadomtsev and Nedospasov for a positive column) resulting from unequal streaming of ions and electrons to the conducting end walls, a phenomenon which should happen above a critical field or below a critical background pressure.