Creating negative ion beams from neutral gases using a negative hydrogen ion source

Abstract

A typical method to produce negative ion beams uses alkali vapour as a medium for a double charge exchange to convert incident positive (1+) beams to negative (1-) beams. Alkali vapours pose a problem in ion production as they are flammable, explosive and cause vacuum surface contamination. Thus, it is advantageous to use non-metallic vapours for charge exchange as it will prevent hazards and the contamination of vacuum surfaces and targets in which the negative ion beams are incident upon. In this paper we will describe and demonstrate the process of creating negative ion beams by impinging a 15 keV to 30 keV beam from D-Pace's TRIUMF licenced H- volume-cusp ion source (1 mA to 15 mA) onto a volume of non-metallic neutral gas (X) resulting in a single or two-step charge exchange: H- + X → H + X- or H- + X → H + X + e → H + X-. The newly created X- ion beams will be accelerated by a (1 to 20) kV electrostatic accelerator and passed through a mass spectrometer system to separate the primary H- beam from the X- beam. The two gases studied are He and H2 and we will present the magnitude of the resultant beam currents after being separated from the incident H- beam by the mass spectrometer system.