Short DCDischarge withWall Probe as a Gas Analytical Detector

A new approach leading to the development of gas analytical detectors is reported. The approach is based on measurements in the near-cathode plasma of fine structures associated with atomic and molecular plasma processes of the high energy portion of the electron energy distribution function (EEDF). A short (without positive column) dc discharge with cold cathode and conducting walls was used. The EEDF measurements in a dc discharge are technically simpler and have dramatically better sensitivity than in the afterglow since temporal resolution is not required. Additional increased probe sensitivity is achieved by using a large-area, larger-radius-of-curvature conducting wall as the probe instead of the more common thin cylindrical Langmuir probe. The wall probe, being almost flat, also greatly reduces the ion current contribution to the measurements. The new approach allows for the development of micro-analytical, dc plasma electron spectroscopy (PLES) gas detectors that are operational up to atmospheric pressure.