Some Features of the Vacuum Arc Ion Source Operation with Lanthanum Hexaboride Cathodes

The paper reports on recent experimental studies of the operation of a vacuum arc ion source with a hot pressed lanthanum hexaboride (LaB6) rod cathode which has a low porosity and almost perfect density (4.65 g/cm
³
). Under normal conditions the resistivity of LaB6, being a refractory ceramic material, is very low and its conductivity is similar to that of metals, and the behavior of cathode spots on the surface of LaB6 is the same as their behavior on pure metals. From cathode spots, the vapors, charged particle flows, a large flow of macroparticles and small cathode fragments is emitted. Such macroparticles bombard the electrodes of the ion-optical system of the source and evaporate, forming a dense plasma, with the result that the acceleration gap is broken down within several milliseconds after vacuum arc extinction. For reducing the flow of macroparticles, the discharge system of the source is equipped with a mechanical direct-flow filter in the region of cathode plasma expansion. The loss of plasma in the filter is compensated by the fields of a permanent magnet and solenoid. The vacuum arc source produces a pulsed (about 300 μs) boron–lanthanum ion beam with a current of 600 mA and diameter of 4 cm with no gas supply.