A dc glow discharge as a source of electrons for a portable mass spectrometer: characterization of the electron current intensity and electron kinetic energy distribution

A dc glow discharge cell with planar electrodes operating at about 1 Torr has been characterized with an inlet flow from ambient air. It will be used as a source of electrons to further ionize molecules by electron impact in a portable mass spectrometer. The Paschen curve has been measured for six values of the pressure around the minimum of the curve. The voltage-current characteristic, observed until 7 mA for different values of the pressure, increases with current in the normal glow regime. The temporal evolution of the discharge current has been recorded over long periods greater than one day for different insulator materials. The best stability has been obtained with Macor and Nylon. The available electron current for ionization has been measured at about 0.6 mu A and the electron kinetic energy distribution has been found to be between 0 and a few tens of eV.