Abstract
The collected current by spherical and cylindrical Langmuir probes immersed in an unmagnetized and collisionless non-Maxwellian plasma at rest are theoretically studied, and analytical expressions for the currents of attracted and repelled plasma particles are presented. We consider Kappa, Cairns and the generalized Kappa–Cairns distributions as possible models for the velocity field in the plasma. The current–voltage characteristics curves are displayed and discussed. Furthermore, comparisons with the collected currents in Maxwellian plasmas are given. The results of Particle-in-Cell (PIC) simulations of spherical and cylindrical probes in non-Maxwellian plasmas are also presented, and compared with the theoretical expressions. The results for the collected currents by the Langmuir probes obtained by PIC simulations are in good agreement with the corresponding analytical expressions.
Highlights
Plasma is often called the fourth state of matter, after solids, liquids and gases [7, Ch 1.1]
For a given κ > 5/2, Before we present the theory and analytical expressions for the currents of plasma particles to a Langmuir probe in a plasma given by the Kappa–Cairns distribution, we will recall the standard assumptions that we make about the ambient plasma and its interaction with the spherical or cylindrical probe
In the following we present the results of PIC simulations for the collected current by positively biased spherical and cylindrical probes
Summary
Plasma is often called the fourth state of matter, after solids, liquids and gases [7, Ch 1.1]. Electrons become energetic enough to break free from molecules, causing a gas of charged particles, where electromagnetic forces between charged particles play a critical role in the dynamics The charged-particle velocity distributions in space plasmas are quite commonly shown to be non-Maxwellian with superthermal tails decreasing as a power-law of the velocity. Such velocity distributions have been measured [3–5], where it was shown that a good fit to the measurements can be achieved for the Kappa/Vasyliunas distribution, which is a generalization of the Maxwellian distribution. A generalized Kappa–Cairns velocity distribution, that effectively blends the former two, has been introduced [9]
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