Beam emittance measurement and plasma channel properties in channel-based ion beam transport

The transport of high-current beams a crucial task in heavy-ion-beam-driven inertial fusion. Plasma-channel-based beam transport is a promising final transport concept which has been studied at the Gesellschaft für Schwerionenforschung (GSI) and at the Lawrence Berkeley National Laboratory (LBNL) in recent years.Aspects of ion beam transport in plasma channels are studied with the beam transport experiment at GSI which is described in this work. Its original setup and recent extension of channel length are discussed. In this experiment, plasma channels are formed by a high-voltage discharge in a background gas. Two methods of channel initiation are investigated: ion beam initiation and laser initiation. The latter uses a laser to create favorable conditions for a discharge along the axis; the former uses the ion beam itself.The properties of ion-beam-induced plasma channels in several gases are studied for a wide range of pressure and voltage for the extended channel length of approximately 1 m. A comparison of different background gases shows that high-Z noble gases are more suitable to create channels for beam transport than low-Z noble gases or nitrogen. The mechanism and limits of laser-initiated discharges with the experimental setup available are discussed. The experiment uses the combination of ammonia gas and a CO2 laser. The parameter range of the two initiation methods and their differences are compared. While laser initiation requires a specific combination of laser and gas, ion-beam-induced channels are theoretically possible with any gas.For final beam transport in a heavy-ion-beam-driven fusion reactor, it is important that the beam quality does not decrease during beam transport. The most important measure of beam quality is the beam emittance. Diagnostics to measure the emittance of the ion beam after transport through the plasma channel are described. Systematic errors due to the measurement setup and the diagnostics are discussed. The particular challenge of measuring the emittance of the beam during beam transport is that the measurement has to be made instantaneously, as all measurements which require a longer time interval cannot be used to investigate changes during beam transport. The results demonstrate the feasibility of measuring beam emittance after a transport channel in a single shot with the setup presented and indicate no changes in the beam emittance within statistical errors