H− and electron production in a magnetic multipole source

Abstract

An investigation has been made of the yield of H⁻ ions and electrons extracted from a magnetic multipole, or bucket, ion source as a function of the parameters of the source. Under optimum conditions the H⁻ current density attains a value equal to half of the positive ion current density (H⁺₃) measured at the extraction plane. The experimental results indicate that, while the H⁻ current rises linearly with arc current, the extracted electron current shows a quadratic dependence. There is also a strong dependence of the electron current on the magnetic field applied across the extraction aperture, and source filling pressure. Probe measurements within the plasma volume show considerable axial variation of the fluxes of electrons, H⁻ ions and H⁺₃ ions.