New infrared imaging diagnostic for the Neutral Beam Heating System at the TJ-II stellarator

An upgraded infrared imaging system has been installed at the stellarator TJ-II as a diagnostic tool of the Neutral Beam Injection heating. Thermographic analysis of the beam-wall interaction areas can be used to estimate the beam power lost through reionization and shine-through mechanisms in Neutral Beam heated plasmas. Three different Regions of Interest inside TJ-II vacuum vessel have been determined whose thermographic analysis will be applied to the study of beam related processes. The optical conditions required for each application have been used to define the specifications of the IR camera. Optimization of the optical design has been carried out by means of the optical simulation code ZEMAX. The IR window size has been increased to maximize the fraction of the field of view that is free from vignetting. The system has been fully commissioned and is now operative, routinely providing thermographic data of the regions of interest during the last TJ-II experimental campaign. The IR diagnostic is described in detail and its applicability to study beam power deposition on different targets is discussed.