Analysis of the Electrode Products Emitted by dc Arcs in a Vacuum Ambient

TLDR

Ion energies exceeding the anode potential may arise from a potential peak near the cathode. The study measured radial and axial ion emissions from dc arcs in vacuum on various cathode materials, finding positive volt‑ampere characteristics over 30–250 A and ion energy distributions peaking above the arc voltage. Axial copper results matched radial copper data, and all examined elements produced significant multiply charged ions; ion energy distributions peaked above the arc voltage, with singly charged fractions rising with current and peak energies shifting lower with higher ionization, higher arc voltage, and higher current.

Abstract

We have examined the particles emitted radially by dc arcs drawn in a vacuum ambient on cathodes of several elements, as well as the axial (through-anode) ion flux from a copper cathode. The axial results for copper agree grossly with the radial copper results. Significant quantities of multiply charged ions were seen for all elements examined. All arc volt-ampere characteristics were positive in the range of currents observed: 30 to 250 A. We drew the following conclusions (normalizing energy in units of ion energy/ion charge): (1) The energy distributions for the various ions are similar, peaking at potentials well above the arc voltage. (2) The fraction of ions that are singly charged tends to increase with increasing arc current. (3) For a given element, as the degree of ionization increases the location of the ion-energy distribution peak shifts to lower energies. (4) For a given degree of ionization, the location of the peak tends toward higher energies for elements with greater arc voltages. (5) The location of the peak shifts toward lower energies as the arc current increases. A possible mechanism for the production of ions with energies corresponding to potentials greater than the anode potential lies in the theory of a potential peak near the cathode.