Negative hydrogen ion production in the hollow cathode Penning surface-plasma source

<jats:p>A small hollow cathode Penning surface-plasma source (SPS) was developed and studied. The H− yield was proportional to the emission apertures area and increased over a wide range of discharge current. The H− yield, with an intensity of up to 0.95 A and an emission current density of up to 3.6 A/cm2, was obtained in a pulsed mode. With the discharge current of 20 A and a pulse duration of 60 s, an H− yield with current of 0.1 A was obtained. The H− emission current density had approximately the same value for various diameters (0.5–7 mm) and thicknesses (0.3–4.0 mm) of cylindrical emission holes, if the thickness of hole walls did not exceed the hole diameter. The H− yield extracted through the thick conical emission holes had a value 25% higher than that for a thin cylindrical hole with the same permeable diameter. Dependencies of the H− yield versus magnetic field and hydrogen feed were different from that of the standard Penning SPS. The optimal cesium coverage of the electrodes was stable for both high-current, long-pulse and low-current, dc source operation. Noticeable H− production was realized with a low-discharge voltage of 15 V. The heavy negative ions fraction was less than 1% of total negative ion yield for long-pulse operation. The yield of D− ions from deuterium discharge had a value 15% lower than that of H− ions from the hydrogen discharge. Most of the extracted H− ions are produced by conversion of fast and superthermal (E≳1 eV) atoms on the cesiated surfaces of the emission hole cones or they are due to the resonant charge exchange of anode-produced H− ions in the volume adjacent to the emission apertures.</jats:p>