Thomson Scattering Diagnostics in the Plasma of an Ion Thruster

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  • YAMAMOTO Naoji
    Department of Advanced Energy Engineering Science, Kyushu University
  • HIRAOKA Yoshiaki
    Department of Advanced Energy Engineering Science, Kyushu University
  • SUGITA Kensaku
    Department of Advanced Energy Engineering Science, Kyushu University
  • KURITA Tomoaki
    Department of Advanced Energy Engineering Science, Kyushu University
  • TOMITA Kentaro
    Department of Applied Science for Electronics and Materials, Kyushu University
  • UCHINO Kiichiro
    Department of Applied Science for Electronics and Materials, Kyushu University
  • NAKASHIMA Hideki
    Department of Advanced Energy Engineering Science, Kyushu University

Abstract

In order to validate the grid erosion evaluation code for the lifetime validation of ion thrusters, the electron number density/temperature in the vicinity of a screen gird in a 30 W class microwave discharge ion thruster were measured by means of laser Thomson scattering (LTS) technique. A photon counting method and a triple grating spectrometer were used against a small Thomson scattering signal and a strong stray laser light. Observed Thomson scattering spectrum tells that the electron energy distribution function was Maxwellian. From this spectrum and the Rayleigh scattering calibration using nitrogen gas, electron number density and electron temperature were calculated to be (3.8±0.2)×1017m-3 and 6.2±0.1 eV, respectively at incident microwave power of 8 W and krypton mass flow rate of 6.2 μg/s. The ion saturation currents estimated from the LTS measurement are in good agreement with ion beam currents through the screen grid for several conditions. These results show that LTS technique is a useful non-intrusive tool for measuring plasma property in the vicinity of the screen grid.

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