A Wire Calorimeter for the SPIDER Beam: Experimental Tests and Feasibility Study

To study and optimize negative ion production and acceleration, in view of the use of neutral beam injectors in the ITER project, the SPIDER test facility (particle energy 100keV; beam current 50A, distributed over 1280 beamlets) is under construction in Padova, with the aim of testing beam characteristics and to verify the source proper operation, by means of several diagnostic systems. An array of tungsten wires, directly exposed to the beam and consequently heated to high temperature, is used in similar experiments at IPP-Garching to study the beam optics, which is one of the most important issues, in a qualitative way. The present contribution gives a description of an experimental investigation of the behavior of tungsten wires under high heat loads in vacuum. Samples of tungsten wires are heated by electrical currents and the emitted light is measured by a camera in the 400-1100nm wavelength range, which is proposed as a calibration tool. Simultaneously, the voltage applied to the wire is measured to study the dependency of emissivity on temperature. The feasibility study of a wire calorimeter for SPIDER is finally proposed; to this purpose, the expected behaviour of tungsten with the two-dimensional beam profile in SPIDER is numerically addressed.