Design And First Results Of A Retractable 1d-Cfc Beam Target For Batman Upgrade

BATMAN Upgrade (BUG) is a test facility for the production of negative ion beams from an RF driven plasma ion source devoted to supporting the development of the ITER Neutral Beam Injection (NBI). BUG consists of the IPP RF prototype source and a multi-aperture grid system corresponding roughly to a beamlet group of the ITER NBI grid system, i.e. an arrangement of 14 (vertical) x5 (horizontal) 014 mm apertures, meaning the ion beam is comprised of 70 individual beamlets. The beams can be extracted with up to 10 kV and accelerated up to a total voltage of 45 kV for up to 10 s (steady state operation is underway). One of the goals of BUG is a detailed study of the ion beam optics. So far, the permanently installed beam diagnostic consisted of several lines of sight of Beam Emission Spectroscopy (BES) at two different positions and thermocouple measurements on the beam dump calorimeter. Resolving the divergence and deflection of single beamlets is technically exceptionally difficult with the existing diagnostic tools, therefore, a beam target made out of a one-directional carbon fiber composite material (1D-CFC) with dimensions 376 x 142 x 20 mm 3 has been installed at a distance of 851 mm from the exit of the grid system. The thermal footprints of the beamlets are observed from the back side via infrared imaging with a high spatial resolution (<0.7 mm/pixel) that allows characterization of the beamlets at low divergence. The target can be rotated out of the beam to make it compatible with long pulses and the forthcoming steady state operation. The safety analysis of the target operation for different operational scenarios is presented together with an energy-based interlock. Finally, the accuracy of estimating the shape of the heat flux on the front of the target from the temperature profile at the back is assessed, based on FEM simulations of a single beamlet.