Experimental investigation of an electronegative cylindrical capacitively coupled geometrically asymmetric plasma discharge with an axisymmetric magnetic field

TL;DR

This study explores how magnetic fields influence negative ion production in an asymmetric cylindrical plasma discharge, revealing that low magnetic fields optimize negative ion yield and that magnetic control is crucial for plasma composition.

Contribution

It provides new insights into the role of axial magnetic fields in controlling negative ion fractions in asymmetric plasma discharges.

Findings

Low magnetic fields enhance negative ion production.

Magnetic fields influence electron temperature and confinement.

Gas mixture ratios and magnetic fields jointly control plasma composition.

Abstract

In this study, we have investigated the production of negative ions by mixing electronegative oxygen gas with electropositive argon gas in a geometrically asymmetric cylindrical capacitively coupled radio frequency plasma discharge. The plasma parameters such as density (electron, positive and negative ion), negative ion fraction, and electron temperature are investigated for fixed gas pressure and increasing axial magnetic field strength. The axisymmetric magnetic field creates an ExB drift in the azimuthal direction, leading to the confinement of high-energy electrons at the radial edge of the chamber, resulting in decreased species density and negative ion fraction in the plasma bulk. However, the electron temperature increases with the magnetic field. It is concluded that low magnetic fields are better suited for negative ion production in such devices. Furthermore, in addition to the percentage ratio of the two gases, the applied axial magnetic field also plays a vital role in controlling negative ion fraction.