Effect of wall material on H− production in a Plasma Sputter-Type Ion Source

Abstract

The effect of wall material on negative hydrogen ion (H⁻) production was investigated in a multicusp Plasma Sputter-Type Ion Source (PSTIS). Steady-state cesium-seeded hydrogen plasma was generated by a tungsten filament while H⁻ was produced through surface production using a molybdenum sputter target. Plasma parameters and H⁻ yields were determined from Langmuir probe and Faraday cup measurements, respectively. At input hydrogen pressure of 1.2 mTorr and optimum plasma discharge parameters V_d = −90 V and I_d = −2.25 A, the plasma parameters n_e was highest and T_e was lowest as determined from Langmuir probe measurements. At these conditions, aluminum generates the highest ion current density of 0.01697 mA/cm² , which is 64% more than the 0.01085 mA/cm² that stainless steel produces. The yield of copper, meanwhile, falls between the two materials at 0.01164 mA/cm². The beam is maximum at V_t = −125 V. Focusing is achieved at V_L = −70 V for stainless steel, V_L = −60 V for aluminum, and V_L = −50 V for copper. Results demonstrate that proper selection of wall material can greatly enhance the H⁻ production of the PSTIS.