Variation of Mass Spectral Line Intensity with Field and Electrode Conditions

An analysis was made of the mass of carriers produced in a vacuum gap under a steady state prebreakdown condition. In order to transport these carriers to a mass analyzer, the cathode probe hole technique is adopted. The configuration of the test electrodes is plane parallel, and the gap length is 0.07 mm. The electrode materials used are Al and Cu. A time-of-flight (TOF) type of mass analyzer with an electrostatic energy filter is employed. Results of mass analysis show that the species of these carriers are identified as ions of hydrogen molecules and those of the electrode materials. For Al electrodes, the main line of the mass spectrum is Al+ at the maximum electric field strength (4.3×105 V/cm), and the relative abundance of Al+ to that of H2+ is 2.6. The value decreases to 0.97 when the applied field is lowered to 4.0×105 V/cm. A fine finish of the electrode surface also decreases the ratio. For Cu electrodes, the abundance of H2+ is maximum over the whole applicable field range.