Diffusion, Ionization, and Sampling Processes in the Glow Discharge Source for Mass Spectrometry

A microsecond pulsed glow discharge source has been coupled to a quadrupole mass analyzer for plasma diagnostics. Diffusion times of sputtered atoms from the cathode surface to the sampling orifice are measured for different cathode orifice distances, pressures, and powers. These measured times are found to be close to the values calculated from the theoretical models, indicating the suitability of this approach to describe the diffusion process in the glow discharge. By comparing ion signal profiles of the gaseous species and sputtered particles and the theoretical atom distributions, evidence is shown that most ions measured by the mass spectrometer are ionized in the vicinity of the orifice.