Reconstruction of the large multi-aperture beam via IR calorimetry technique and beam emission spectroscopy at the ELISE test facility

Abstract

The ELISE test facility with its half ITER size ion source is an important intermediate step in the European development roadmap toward the ITER neutral beam injection system. Of particular interest is the beam characterization at ELISE in terms of homogeneity and divergence. The two main beam diagnostic systems are beam emission spectroscopy (BES), providing beam intensity and divergence and infrared (IR) calorimetry applied to the surface of a diagnostic calorimeter, which provides a spatially resolved 2D map of the beam power density. Beam parameters such as width, intensity, position and accelerated current are retrieved by a fitting routine which is validated using synthetic beam profiles, thus demonstrating that the beam parameters are correctly reproduced. By comparing results of BES and IR calorimetry for several thousand pulses, it is demonstrated that the beam width is, to a large extent, determined by the beam divergence. BES and IR calorimetry are then combined to reconstruct the beam profile and this is the basis to investigate procedures for improving the beam quality in terms of power density homogeneity.