The respone of a spherical plasma probe to alternating potentials: Results of computations and use for plasma diagnostics

Abstract

In a previous paper, the R.F. characteristics of a spherical probe immersed in a hot, low-density plasma using a realistic sheath model were considered, and a few results of computations presented. The remainder of these results are given in this paper. The dependences of R.F. admittance, and rectified current on probe radius, d.c. bias, and electron neutral collision frequency are exhibited and shown to be qualitatively in accord with the predictions of simple slab-sheath/dielectric models. It is shown how in principle, analysis of resonance rectification characteristics using curves included in the paper can yield values of electron density n e temperature T e , and electron-neutral collision frequency ν. Two methods of reduction are applied to some laboratory results obtained at Slough and are shown to give reasonably consistent values of n e and ν, but the values of T e , show considerable scatter. These methods could complement the Langmuir probe which gives more reliable values of T e than of n e in low density plasmas with n e ≾10 8 cm −3 . Effects of magnetic fields are not included in this paper.