Study for Emittance Measurements in a High-Current Multibeamlet Beam

SPIDER is the prototype beam source of the ITER Heating Neutral Beam injector. A movable diagnostic calorimeter will be used as a direct mean to obtain the beam footprint in short-pulses, while a fixed beam-dump is installed for steady-state operation. For the comparison between experiment and numerical simulations of ion beam extraction, measuring the beam emittance is extremely useful, being the most complete characterization for a particle beam. We discuss in this paper two proposals for beam-emittance measurements in SPIDER: at high beam energies, a fixed electric-sweep scanner is proposed for integration in the water-cooled beam-dump; at relatively low beam energies, a movable emittance scanner is proposed for the installation on the movable diagnostic calorimeter. The synthetic signals of the scanner are calculated considering the multibeamlet setup. The constraints given by the integration in high heat load components and the thermal design are discussed. The fixed ESS can be used to reconstruct the beam divergence, even if it detects only a limited section of the beamlet emittance, if identical single-beamlet optics is assumed. The movable emittance scanner is easy to integrate in the present design, and allows a full characterization of the single beamlet optics.