  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.
