Diffusion Model of Saturation Current Collection by a Planar Langmuir Probe in a Strong Magnetic Field

Abstract

AbstractPlasma presheath and saturation current collection by a planar Langmuir probe in a strong magnetic field perpendicular to the probe surface ares described with the diffusion model. The model takes into consideration the geometry of the probe, that is its size and shape, and dependence of the cross‐field charged particles' transport into the effective collection region of the probe on the parallel‐field transport to the probe. Experimental study of planar Langmiur probe I—V characteristics in D.C. discharge argon plasma in strong magnetic fields confirms the possibility of deriving the cross‐field diffusion coefficient, D, from the measured electron satuation current. Additional dependence of the electron saturation current on the parallel‐field diffusion coefficient, D, and the ion temperature, Ti, derived in the approximate Stangeby's study using the diffusion model of current collection by a planar surface (Stangeby, P. C., J. Phys. D: Appl. Phys. 15 (1982) 1007) can be eliminated with more rigorous calculation. Series of measurements on two neutral pressures and various magnetic fields gave reproducible values of D, approximately given by relation D ≈ (δn/〈n〉) kBTe/(eB).