Langmuir probe diagnostics of continuous, electron beam produced plasma in argon, nitrogen and their mixtures

Langmuir probe diagnostics have been carried out in the Naval Research Laboratory’s Large Area Plasma Processing System (LAPPS) using a continuous, electron-beam produced plasma. The electron beam was extracted from a hollow-cathode discharge, accelerated using a high-voltage grid and a magnetic field was applied to confine the beam. The plasma was produced in a background of pure argon, nitrogen and their mixtures. The generated plasma had a high density 10⁹–10¹¹ cm⁻³ like the conventional discharges but a lower electron temperature (≪ 1 eV) which allows for the processing of energy-sensitive materials. The effect of the operating parameters including hollow cathode and extraction voltages and currents on the plasma characteristics was examined. Further tuning of the plasma properties was achieved by adjustment of the magnetic field and the gas composition.