Angle-resolved ion charge state distribution measurements in a vacuum arc plasma using time-of-flight mass spectroscopy

Abstract

Summary form only given. In vacuum arc discharges the current is conducted through vapor evaporated from the cathode surface, creating very dense, highly ionized plasmas from any metallic or conducting solid. Vacuum arc sources are currently used for ground-based material deposition systems and to form very high energy, heavy ion beams for fusion applications. Space propulsion engines using vacuum arc sources can be operated efficiently with a range of propellant options that gives great flexibility in specific impulse. In addition, the efficiency of plasma production in these devices appears to be largely independent of scale because the metal vapor is ionized within a few microns of the cathode electron emission sites, so this approach is well-suited for micropropulsion. The ion charge state distribution influences the efficiency of these devices and the behavior of the plasma plume. In addition, this parameter provides considerable insight into the physics of plasma production in the emission site. Charge state distributions have been measured on the centerline of vacuum arc plasma accelerators, but there are no measurements of the angular distribution of charge state in the plume of vacuum arc discharges. A time-of-flight mass spectrometer has been developed to measure the distribution of charge states in the plumes of vacuum arc discharges as a function of angle, material and current. This paper describes the design and fabrication of the instrument and preliminary results of angle-resolved measurements of charge state distribution in titanium vacuum arcs.