Negatively Charged Oxygen Ions as a Plasma Diagnostic Tool: Application to Comets

Sreekala Gopinathan¹, Sijo Sebastian¹, Noble Abraham¹, Savithri Devi¹, Venugopal Chandu^1*, Renuka Gangadharan²

¹School of Pure & Applied Physics, Mahatma Gandhi University, Kottayam, India.
²Kerala State Council for Science, Technology & Environment, Thiruvananthapuram, India.

DOI: 10.4236/oalib.1100570                

Abstract

We study the stability of the ion-acoustic (IA) wave in a collisional plasma composed of hydrogen, positively and negatively charged oxygen ions, electrons and neutral atoms. This composition approximates very well the plasma environment around a comet. A solution of the dispersion relation yields a frequency for the IA wave at around the hydrogen plasma frequency. The growth/ damping rate is sensitively dependent on the ring parameters μ _⊥s (the ring speed) and ν _ts (the thermal spread). The growth rate of the wave, which decreases with increasing collisional frequencies, is larger when μ _⊥s < ν _ts. In the presence of negatively charged oxygen ions, the phase and group velocities of the IA wave behave in a contrasting manner when μ _⊥s < ν _ts (and viceversa). We propose that this behaviour be exploited as a diagnostic tool for the detection of these ions and also their thermalization.

Keywords

Ion-Acoustic Wave, Negative Ions, Diagnostic Tool, Cometary Plasma

Conflicts of Interest

The authors declare no conflicts of interest.

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