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Investigation of a low - temperature cesium plasma in a low-voltage arc

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Abstract

The electron temperature Te and electron concentration ne in a cesium plasma in a low-voltage arc have been measured at an electrode temperature of 700°C using the double probe method. The distribution of Te and ne in the interelectrode gap d=9.8 mm is obtained in the investigated range of pressures, P = =5.7 · 10−3-5 · 10−1 mm Hg. The distribution ne=f (x) has a maximum near the cathode. Te and ne are obtained as a function of the discharge current Ip=1–3 a, and a qualitative description of the burning mechanism for a low-voltage arc is given.

The behavior of a low-temperature cesium plasma is currently of great interest in connection with its use in thermionic and MHD devices for the direct conversion of thermal energy into electricity.

One of the most interesting manifestations of such a plasma is the low-voltage arc. A thermionic converter operating in the diffusion regime at some cathode temperature (of the order of 1300–1400°C), which depends upon the cesium pressure and the length of the interelectrode gap, spontaneously goes over into the low-voltage arc regime. The latter is the most promising operating regime for the converter.

The low-voltage arc in inert gases and mercury vapor is already familiar [1]. In 1951, Medices observed a low-voltage arc during thermionic conversion of thermal energy into electricity in a xenon atmosphere [2]. One of the fundamental problems in investigating the low-voltage arc is accounting for the burning mechanism, particularly when the burning potential is lower than the first excitation potential of the gas in which the arc burns.

In order to understand the burning mechanism of the low-voltage arc one must know the parameters of the gas discharge plasma and their distribution in the interelectrode gap. A very satisfactory qualitative explanation of the burning mechanism, based on the experimental fact of the existence of a maximum in the plasma potential and density distributions in the interelectrode gap near the cathode, has been given by Druyvesteyn [3].

Steinberg [4] and N. D. Morgulis [5], investigating low-voltage arc plasma parameters in cesium vapor by the single probe method, did not detect plasma density and potential maxima in the interelectrode space.

This article is concerned with a study of the distribution of electron temperature Te and electron concentration ne in a low-voltage arc (LVA) along the axis of the interelectrode gap and the effect on Te and ne of a cesium vapor pressure of 5 · 10−3 to 5 · 10−1 mm Hg and a discharge current in the range 1–3 a.

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References

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In conclusion, the author wishes to express his appreciation to V. N. Glazanov for his continuous interest in the work and I. P. Stakhanov and I. I. Kasikov for their useful comments.

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Lebedev, M.A. Investigation of a low - temperature cesium plasma in a low-voltage arc. J Appl Mech Tech Phys 6, 34–37 (1965). https://doi.org/10.1007/BF00915608

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Keywords

  • Cesium
  • Burning Mechanism
  • Cesium Vapor
  • Double Probe
  • Thermionic Conversion