Speaker
Avnish Kumar Pandey
Description
See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P1.4012.pdf
Using biased hairpin probe for determining oxygen negative Ions in a
double plasma device
A K Pandey1, S K Karkari2
1
Institute for Plasma Research, Gandhinagar, India
2
Institute for Plasma Research, Gandhinagar, India
The hairpin probe is a quarter-wave transmission line. The probe exhibits a resonance which
is determined by the dielectric constant of the medium surrounding the hairpin. When
immersed in the plasma, the observed resonance relates to the electron plasma frequency
through the plasma dielectric constant. Hence the electron density, ne, can be directly found
using this technique. The hairpin probe had been used as a detection probe in pulse laser
photo-detachment of negative ions. In this paper we demonstrate that the hairpin probe can
also act as a Langmuir probe to determine α (ratio of negative ion density and electron
density). It is observed that on applying positive bias to the hairpin, the resonance frequency
shifts towards higher values, reaching saturation at the plasma potential. The positive ion
density is determined from the ion saturation region, based on OML theory. It has been found
that the OML theory is suitable for calculating the positive ion density, showing excellent
match with the electron density obtained by hairpin resonance in electro-positive argon
plasma. Using this method, the value of α has been determined in oxygen discharge in a
double plasma device. Experimental results show a decreasing trend in α on increasing the
power levels, consistent with the previous results.
Reference:
[1] Stenzel R L 1976 Rev. Sci. Instrum. 47 603.
[2] A. K. Pandey and S. K. Karkari, Phys. Plasmas 24, 013507 (2017).
