Design and specifications of the diagnostics for the instrumented calorimeter of SPIDER

Operation of the thermonuclear fusion experiment ITER requires additional heating via injection of neutral beams from accelerated negative ions. In the SPIDER test facility, under construction in Padova, the production of negative ions will be studied and optimised. This test bed will aim at assessing beam characteristics and verifying the source proper operation. STRIKE (Short-Time Retractable Instrumented Kalorimeter Experiment) is a diagnostic used to characterise the SPIDER beam during short operation (several seconds) to verify if the beam meets the ITER requirement about the maximum allowed beam non-uniformity (below ±10%). During long pulse operations, STRIKE is parked off-beam in the vacuum vessel. The most important measurements performed by STRIKE are beam uniformity, beamlet divergence and stripping losses. This contribution gives an overview of the diagnostics dedicated to these measurements: thermal cameras to measure the temperature pattern on the rear side of the tiles; current sensors to measure the current associated to the beam particles; thermocouples, giving a local temperature measurement, to provide a calibration for thermal cameras; electrostatic sensors to characterise the plasma formed by the interaction of the beam with the background gas. In order to prevent secondary electrons from escaping the tile surface, a voltage is applied to the tiles with respect to the vacuum vessel. The specifications of these diagnostics have been defined according to the results of electrostatic and thermal simulations. A failure modes and effects analysis has been performed during the design. Consequently the project of the STRIKE diagnostics has been optimized to reduce the possible failure risks. This work was set up in collaboration and financial support of F4E.