Hydrogen negative ion source with LaB6 inserts

The compact negative ion source having a semiplanotron discharge geometry a nd the two independently heated LaB6 cathode inserts was developed and stud ied. The hot LaB6 cathode insert supports discharge ignition and operation at low hydrogen pressure, while the cold one provides the glow discharge co ncentration in its vicinity. The stable production of H- beams with the cur rent density in the emission hole in the range of about 0.1 A/cm(2) was obt ained in the pure hydrogen discharge. Negative ion yield at the different p arts of the composite source cathode was measured. It was maximal in the gl ow region. An enhanced H- yield was recorded due to discharge concentration near the LaB6 inserts. LaB6 with a decreased work function does not produc e a sizable income of surface-produced negative ions to the beam, extracted from the pure hydrogen discharge. The use of LaB6 inserts as a reliable so urce of electrons to form the discharge simplifies the surface-plasma sourc e use. (C) 2000 American Institute of Physics. [S0034-6748(00)50402-X].