Recent advances in high current vacuum arc ion sources for heavy ion fusion

dFor a heavy ion fusion induction linac driver, a source of heavy ions with charge states I + -3 +, approximate to 0.5A current beams, approximate to 20 mus pulse widths and similar to 10 Hz repetition rates is required. Ther mionic sources have been the workhorse for the Heavy Ion Fusion (HIF) progr am to date, but suffer from heating problems for large areas and contaminat ion. They are limited to low (contact) ionization potential elements and of fer relatively low ion fluxes with a charge state limited to 1 +. Gas injec tion sources suffer from partial ionization and deleterious neutral gas eff ects. The above shortcomings of the thermionic ion sources can be overcome by a v acuum are ion source. The vacuum are ion source is a good candidate for HIF applications. It is capable of providing ions of various elements and diff erent charge states in short and long pulse bursts and high beam current de nsity. Under a Phase-I STTR from DOE, the feasibility of the vacuum are ion source for the HIF applications was investigated. We have modified an existing va cuum are ion source at LBNL to produce a gadolinium (A approximate to 158) ion beam with > 0.5A beam current, 120 keV beam energy, approximate to 6 cm diameter extraction aperture and approximate to 20 mus pulse width. The av erage beam current density at the extraction grids was approximate to 17 mA /cm(2). We have measured that > 85% Gd ions were in the 3 + charge state, t he beam current fluctuation level (rms) was approximate to 3%, pulse-to-pul se variation of the beam (rms) was about 3%, the uniformity of the beam den sity over its 6 cm diameter was greater than or equal to 98% and the ion lo ngitudinal energy spread was less than or equal to1%. Additional measuremen ts were made to improve charge state purity by using other materials and em ploying an axial magnetic field close to the cathode. Yttrium (cl approxima te to 89, lead (A approximate to 207), and B(Ai approximate to 137) were te sted at similar current parameters with Ba delivering nearly a purl charge state with >95% being in 2 + state. The results of the experiments indicate that the vacuum are ion source is a good candidate for HIF applications. ( C) 2001 Elsevier Science B.V. All rights reserved.