K+ ion source for the heavy ion induction linac system experiment ILSE

Low emittance singly charged potassium thermionic ion sources are being developed for the ILSE injector. The ILSE, now under study at LBL, will address the physics issues of particle beams in a heavy ion fusion driver scenario. The K⁺ ion beam is emitted thermionically into a diode gap from alumino-silicate layers (zeolite) coated uniformly on a porous tungsten cup. The injector diode design requires a large diameter (4" to 7") source able to deliver a high current (~ 800 mA) low emittance (E_n<.5π mm-mr) beam. The SBTE (Single Beam Test Experiment) 120 keV gun was redesigned and modified with the aid of diode optics calculations using the EGUN code to enable the extraction of high currents of about 90 mA out of a one-inch diameter source. We report on the 1" source fabrication technique and performance, including total current and current density profile measurements using Faraday cups, emittance and phase space profile measurements using the double slit scanning technique, and lifetime measurements. Furthermore, we shall report on the extension of the fabricating technique to large diameter sources (up to 7"), measured ion emission performance, measured surface temperature uniformity and heating power considerations for large sources