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Characterization of the Electron Energy Distribution Function of Plasma Sphere in the Inertial Electrostatic Confinement Device with Optical Emission Spectroscopy and Collisional-Radiative Model

ORAL

Abstract

The discharge behavior within inertial electrostatic confinement (IEC) devices is not yet fully understood. A working principle based on the double-layer theory is proposed to explain the discharge mechanism. [1-3] Optical emission spectroscopy (OES) is used to evaluate the non-Maxwellian electron energy distribution function (EEDF) and the respective effective electron temperature (Te) across the radius of the plasma sphere within the IEC. An optimized super-symmetrical cathode structure is implemented for the IEC device to reduce the uncertainty of the discharge [4] and argon is used as the demonstrating gas for the evaluation.

The prediction of the EEDF and Te is performed through the collisional radiative model [5,6]. The x-form formula proposed by Davydov-Druyvesten is used to interpret the non-Maxwellian EEDF. [5] The line-ratio of transition 420.06 nm and 419.87 nm is used to determine the EEDF of the experimental measurement.

The Te at the center of the plasma sphere aroud 20 eV and decays to 2 eV at the edge of plasma sphere. The Te profile across the radius of the plasma sphere presents strong non-linearity, so as the EEDF profile. This proves the formation of a virtual anode at the center of plasma sphere, which dominates the discharge mechanism of IEC device.

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Publication: [1] Y.-A. Chan and G. Herdrich, "Inertial Electrostatic Confinement: Innovation for Electric Propulsion and Plasma Systems," in 35th <br> International Electric Propulsion Conference, Atlanta, GA, USA, 2017, no. IEPC 2017-599.<br>[2] M. A. Raadu, "The Physics of Double Layers and Their Role in Astrophysics," Physics Reports, vol. 178, no. 2, pp. 25–97, 1989, <br> doi: 10.1016/0370-1573(89)90109-9.<br>[3] C. Charles, "A review of recent laboratory double layer experiments," Plasma Sources Science and Technology, vol. 16, no. 4, pp. <br> R1–R25, 2007, doi: 10.1088/0963-0252/16/4/r01.<br>[4] Y.-A. Chan and G. Herdrich, "Influence of Cathode Dimension on Discharge Characteristics of Inertial Electrostatic Confinement <br> Plasma Thruster," in 36th International Electric Propulsion Conference, Veinna, Austria, 2019, no. IEPC-2019-293.<br>[5] J. B. Boffard, C. C. Lin, and A. E. Wendt, "Application of Excitation Cross-Section Measurements to Optical Plasma Diagnostics," <br> in Advances In Atomic, Molecular, and Optical Physics, vol. 67, E. Arimondo, L. F. DiMauro, and S. F. Yelin, Eds. Academic Press, <br> 2018, pp. 1–76.<br>[6] J. B. Boffard, R. O. Jung, C. C. Lin, L. E. Aneskavich, and A. E. Wendt, "Optical diagnostics for characterization of electron <br> energy distributions: Argon inductively coupled plasmas," Plasma Sources Science and Technology, vol. 20, no. 5, 2011, doi: <br> 10.1088/0963-0252/20/5/055006.

Presenters

  • Yung-An C Chan

    Institute of Space Systems, University of Stuttgart

Authors

  • Yung-An C Chan

    Institute of Space Systems, University of Stuttgart

  • Georg Herdrich

    Institute of Space Systems, University of Stuttgart