Design and preliminary measurements of a diagnostic calorimeter for BATMAN

Abstract

The ITER project requires neutral beam injection; such additional heating power will be provided by two injectors accelerating negative ions. To study and optimise negative ion production, the SPIDER prototype is under construction in Padova, Italy, whose beam has an energy of 100 keV and a current of 50 A. The instrumented calorimeter STRIKE (Short-Time Retractable Instrumented Kalorimeter Experiment) has been designed with the main purpose of characterising the SPIDER negative ion beam in terms of beam uniformity and beam divergence during short operations (several seconds). STRIKE is made of 16 1D Carbon Fibre Composite (CFC) tiles, intercepting the whole beam and observed on the rear side by infrared (IR) cameras. With two identical samples of the CFC material and with the IR camera under assessment, a reduced version of the entire calorimeter has been built, with the purpose of characterising its diagnostic properties. This mini-STRIKE was used in the BATMAN experiment at IPP (Garching, Germany). As the beamlet divergence in BATMAN is large, the beamlets are superposed in the position where the diagnostic is located; consequently the mini-STRIKE for BATMAN includes a copper mask, facing the beam and featuring 8 apertures. Thus, eight different portions of the beam can be simultaneously sampled, with minimal overlapping of the power coming from adjacent apertures. The copper mask was actively cooled and calorimetry was carried out. The temperature in the centre of the mask and in some positions along the CFC tiles was also measured. In this contribution the design of the system is presented, along with the tests performed before the installation of mini-STRIKE in BATMAN. The calorimetry system is presented in detail as well as the procedure adopted for calorimetrical data analysis. Results of calorimetry are presented together with preliminary correlations with the BATMAN beam features.