GAS-BREAKDOWN EFFECTS IN THE GENERATION AND TRANSPORT OF LIGHT-ION BEAMS FOR FUSION

The efficiency of delivering an ion beam to an inertial confinement fu sion target depends on the ability to control the breakdown of both un intended (in the ''vacuum'' diode region) and intended (in the transpo rt region) gas. The desorption and breakdown of anode-surface contamin ants in an ion diode complicates the generation of a pure, high-bright ness ion beam. Beyond the accelerator, the gas in the reactor vessel m ust provide excellent charge neutralization and specified current neut ralization to permit the beam transport and focusing to a <1 cm radius , spherical target. Two schemes, in which controlling gas breakdown is essential, are ''ballistic'' and ''self-pinched'' ion transport. Resu lts are discussed from hybrid particle-fluid simulations of anode cont aminant desorption and ion beam transport. (C) 1996 American Institute of Physics.