Effect of finite electrode area ratio on high-frequency Langmuir probe measurements

M. Shimoyama, Oyama Koichiro, T. Abe, A. W. Yau

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Abstract

Langmuir probe (LP) measurement generally requires a reference electrode with large surface area compared with that of a probe. Whereas a reference electrode with large surface area is available in laboratory experiments, surface area of the reference electrode is limited when the probe is installed on a small spacecraft such as a sounding rocket. Insufficient electrode area ratio of the reference electrode to the probe leads to distortion of the currentvoltage (IV) characteristics and therefore the derived electron temperature and density might be erroneous. In order to investigate the effect of finite electrode area ratio on LP measurements, we have carried out a laboratory simulation by setting up a model sounding rocket with whole apparatus for LP measurement in a vacuum chamber. By changing the frequency of sweep voltage applied to the probe from 0.1Hz to 3kHz, we have derived an equivalent resistance and capacitance of the reference electrode sheath, which was thought to be the principal cause of distortion in IV characteristics. The result shows that when the electrode area ratio is 124, the electron temperature is unaffected by the impedance of the reference electrode while the electron density is underestimated by 50%. In addition, the high sweep frequency method introduced here turned out to be an effective approach to make measurements with LP possible even when a sufficient surface area ratio cannot be achieved.

Original languageEnglish
Article number075205
JournalJournal of Physics D: Applied Physics
Volume45
Issue number7
DOIs
Publication statusPublished - 2012 Feb 22

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All Science Journal Classification (ASJC) codes

  • Electronic, Optical and Magnetic Materials
  • Condensed Matter Physics
  • Acoustics and Ultrasonics
  • Surfaces, Coatings and Films

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