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 fusion target depends on the ability to control the breakdown of both unintended (in the ‘‘vacuum’’ diode region) and intended (in the transport region) gas. The desorption and breakdown of anode-surface contaminants in an ion diode complicates the generation of a pure, high-brightness ion beam. Beyond the accelerator, the gas in the reactor vessel must provide excellent charge neutralization and specified current neutralization 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. Results are discussed from hybrid particle-fluid simulations of anode contaminant desorption and ion beam transport.