Honeycomb surface-plasma source of negative ions

A new honeycomb surface-plasma source of negative hydrogen ions is described. The cathode is a large array of cells with spherically concave surfaces. The negative ions ejected from the cathode by fast particles from a cesium--hydrogen discharge are accelerated in the potential-drop layer near the cathode and are focused geometrically into small emission apertures in the anode. The effect is to raise the gas and energy efficiencies of the source and to reduce the power density dissipated at the cathode. The yield of H- ions is proportional to the number of cells. A pulsed beam of negative ions with a current up to 4 A has been produced and accelerated to 25 kV from a working cathode surface area of 10.6 cm2 through emission windows with a total area of 0.5 cm2. Honeycomb surface-plasma sources with more cells hold promise for producing beams of negative ions with a current of tens of amperes