Ion source with LaB6 hollow cathode for a diagnostic neutral beam injector

In this article ion source capable of providing 8 A, 54 keV proton beam in maximum 3 s pulses is described. A general description of the diagnostic injector based on this ion source is also given. The ion beam is extracted and accelerated by a four-electrode multiaperture ion-optical system. In the ion source, hydrogen (deuterium) plasma is generated by an arc discharge plasma box with a hot LaB6 cathode. The plasma jet diverging from a small anode orifice enters the plasma expansion volume with a peripheral multipole magnetic field and after partial reflection from this field forms a uniform plasma emitter of 160 mm in diameter in the plasma grid plane. The plasma box operates with an arc current of 350-700 A, providing more than 75% of full energy specie in the extracted ion beam. The ion beam is subsequently neutralized in a hydrogen target with similar to 50% efficiency and is focused 4 m downstream from the ion source that is provided by a spherical shape of the grids. The beam angular divergence is 0.6 degrees. The ion source is used for plasma diagnostics at Alcator C-mod tokamak. (c) 2006 American Institute of Physics.