Beam Emittance Measurement for Channel-based Ion Beam Transport

The transport of high-current beams is a crucial task in heavy-ion-beam-driven inertial fusion. Plasma-channel-based beam transport is a promising nal transport concept which has been studied at the Gesellschaft f¤ ur Schwerionenforschung and at the Lawrence Berkeley National Laboratory in recent years. Aspects of ion beam transport in plasma channels are studied with the Z4 beam transport experiment at GSI. In this experi- ment, plasma channels are formed by a high-voltage discharge in a background gas. For any nal beam transport scheme in a fusion reactor which includes drift space, it is important to know whether the beam quality decreases during beam transport. The most important measure of beam quality is the beam emittance. The partic- ular challenge in a beam transport setup is an instantaneous measurement of the beam emittance, since all scanning mea- surements cannot be used to investigate changes during beam transport. The beam is sent through the transport channel, then passes a gold pepper-pot foil of 35 m thickness and a drift space of sev- eral centimeters before it is made visible on a plastic scintillator which is photographed by a fast CCD camera. The integration of the emittance diagnostics into the setup is shown in Fig. 1.