Investigation of helium ion production in constricted direct current plasma ion source with layered-glows.
Generation of helium ions is experimentally investigated with a constricted direct current (DC) plasma ion source operated at layered-glow mode, in which electrons could be accelerated through multiple potential structures so as to generate helium ions including He(2+) by successive ionization collisions in front of an extraction aperture. The helium discharge is sustained with the formation of a couple of stable layers and the plasma ball with high density is created near the extraction aperture at the operational pressure down to 0.6 Torr with concave cathodes. The ion beam current extracted with an extraction voltage of 5 kV is observed to be proportional to the discharge current and inversely proportional to the operating pressure, showing high current density of 130 mA/cm(2) and power density of 0.52 mA/cm(2)/W. He(2+) ions, which were predicted to be able to exist due to multiple-layer potential structure, are not observed. Simple calculation on production of He(2+) ions inside the plasma ball reveals that reduced operating pressure and increased cathode area will help to generate He(2+) ions with the layered-glow DC discharge.
Some characteristics of the hollow anode glow
A new type of discharge realized in a diode consisting of a cathode and a special type of hollow anode is presented. The distinctive arrangement of dark and luminous regions between the cathode and anode with a characteristic hollow anode glow has been observed in the discharge. The optical spectrum strongly depends on the discharge current, and can be practically a spark or arc spectrum without any lines of anode or cathode material.
Cylindrical hollow‐anode discharge
Hollow‐anode discharge represents a new type of discharge which is realized in a diode consisting of a cylindrical cathode and special type of hollow anode whose inner surface only is conductive. The cylindrical cathode focuses electrons toward the hollow anode placed in the center of curvature, increasing the density of high‐energy electrons and efficiency of excitation and ionization in the hollow aperture of the anode. Optical spectrum consists of intense ion lines of the operating gas without anode or cathode material lines.