  This work shows the development of a volume-produced negative ion source that
consists of annular parallel plates driven by a 13.56 MHz capacitively coupled
radio frequency in a push-pull configuration. This source shows advantages in
controlling plasma conditions by varying the pressure, power, and applied axial
magnetic field. It is found that the push-pull configuration allows the plasma
potential to remain in the range of 20 to 40 Volts. Conversely, the application
of a magnetic field helps serves to augment the production of negative ions in
the central hollow part of the annular plate. Further, a plausible explanation
to the obtained experimental results is presented.
