Particle Sensors in Ionospheric Plasma: Study of Langmuir Probes with Kinetic Simulations

• Author / Creator

  Resendiz Lira, Pedro Alberto

• Particle collection by Swarm spherical probes, and front plate when used as a planar Langmuir probe, is studied for representative ionospheric plasma conditions.
  The objective is to assess uncertainties in the plasma parameters inferred from probe measurements using analytic models.
  Probe in situ measurements are generally interpreted in terms of plasma parameters on the basis of theoretical approaches.
  Swarm spherical probe measurements are interpreted in the Orbital Motion Limited (OML) approximation, while the front plate has assumed the following relation between the measured collected current I, e the elementary charge, the ion density n, the plasma flow velocity to the plate v{ram}, and the known geometrical surface of the plate, I=env{ram}A{geo}.
  In such models, several assumptions or asymptotic limits are considered in order to obtain analytical solutions.
  Probe collected currents are calculated numerically and interpreted as in actual Swarm in situ measurements.
  Kinetic simulations are done while accounting for more physical effects than can be accounted for analytically.
  For the spherical probes, simulations also account for the main aspects of the probe geometry and its proximity to the Swarm bus.
  By comparing inferred parameters from simulated probe measurements with the known ones used as input in the simulations, it is possible to assess relative errors resulting from the use of analytic expressions.
  OML predictions of the electron temperature inferred from spherical probe measurements are found to be moderately accurate, with relative errors not exceeding 12%, when the satellite floating is moderate negative.
  As the spacecraft floating potential becomes more negative, more electron are repelled and the electron currents collected by the probes are reduced, impacting then the estimates of the inferred temperatures by up to 48%$.
  The maximum errors are mainly caused by the neglect of magnetic field and satellite sheath effects in the OML theory.
  The estimates of the plasma density on the other hand, are significantly less accurate, with relative errors up to 76%.
  Here, discrepancies are attributed mostly to the neglect of minority light ions, and the satellite electric sheath, which can extend to, and include the tip of the spherical Langmuir probes.
  Simulation results of the Swarm front plate led to the conclusion that the effective cross section A{eff} is generally larger than the geometrical A_{geo} which is consistent with observations.
  The current collected by the plate is enhanced from 2.8 to 23.4% with respect to the one collected by the geometrical cross-section, where this enhancement is attributed to fringe effects.
  Simulation results from the front plate are used then to construct an empirical model for the collected current by the plate accounting for the enhancements, and in turn enable improvements in the accuracy of inferred plasma parameters.

• Subjects / Keywords

  • PIC Simulations
  • Langmuir Probes
  • Space Plasma Physics
  • Particle Sensors

• Graduation date

  Fall 2019

• Type of Item

  Thesis

• Degree

  Doctor of Philosophy

• DOI

  https://doi.org/10.7939/r3-cq2b-z829

• License

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