Two dimensional PIC simulation of a Langmuir probe in a plasma beam

Abstract

Summary form only given, as follows. A 2d/3v electrostatic particle-in-cell (PIC) code has been developed to simulate a Langmuir probe in a plasma beam. The code was written to enable the use of the Langmuir probe in plasma regimes for which no closed-form analytical solutions exist; this is the case for a probe in an ion beam, such as the plume of an ion thruster. Langmuir probes are used to determine local plasma properties, such as electron temperature, by careful dissection of the probe's V-I characteristic. To interpret experimental data from a Langmuir probe, one must separate ion from electron current. This process is well documented for quiescent plasmas; however, no systematic techniques are available for interpreting data obtained using an electric probe in an ion beam ad hoc estimates of probe ion current in beam plasmas may lead to order of magnitude errors in the calculation of electron temperature. The PIC code described in this paper was written to elucidate the beam-probe interaction and provide systematic techniques for legitimately interpreting experimental data. Elements of the PIC technique in general will be discussed; in particular, methods used in fluxing particles across boundaries. Code results will be presented. Code and theoretical probe traces for an infinite cylindrical probe in a quiescent plasma will be shown to be in agreement. Also, code results for a plasma beam will be compared with experimental data from the UTSI three-grid ion thruster.