Parametrization of current-voltage characteristics and operation domains of cylindrical emissive probes in collisionless Maxwellian plasmas at rest Articles uri icon

publication date

  • November 2021

start page

  • 115018

issue

  • 11

volume

  • 63

International Standard Serial Number (ISSN)

  • 0741-3335

Electronic International Standard Serial Number (EISSN)

  • 1361-6587

abstract

  • Important progress has recently been made on the Orbital Motion Theory for cylindrical
    emissive probes immersed at rest in collisionless and Maxwellian plasmas. However, due to the computational cost of its numerical algorithm, only solutions for specific values of the physical parameters were found, thus preventing its direct application to the interpretation of
    experimental current–voltage characteristics (Ip − Vp curves). In this work, and thanks to an
    analytical analysis of a Jacobian matrix appearing in the algorithm, the computational cost was
    reduced by a factor in the order of Nr, where Nr is the number of grid points. This achievement,
    together with the implementation of parallel programming, allowed to construct a database with
    more than 18 000 Ip − Vp curves for a broad range of physical parameters, including the
    emission level, the probe radius-to-Debye length, and the ion-to-electron temperature ratios.
    The boundaries in parameter space of the operational regimes of emissive probes, covering both
    orbital motion limited (OML) and space charge limited (SCL) transitions were computed. A
    novel OML/non-OML transition for emissive probes operating at low bias was found. The
    numerical results were used to propose useful analytical laws for the SCL boundary happening
    at negative bias, the reduction of the emitted electron current due to SCL effects, and the
    floating potential of emissive probes. The applications of the results to the modeling of low
    work function tethers and three experimental methods for measuring the plasma potential, i.e.
    the separation point, the inflection point, and the floating potential techniques, were discussed. The formation of an inverse sheath for strong emission was investigated.

keywords

  • emissive probes; current-voltage characteristics; orbital motion theory