In-vessel calibration of the imaging diagnostics for the real-time protection of the JET ITER-like wall

Abstract

The in situ absolute calibration of the JET real-time protection imaging system has been performed for the first time by means of radiometric light source placed inside the JET vessel and operated by remote handling. High accuracy of the calibration is confirmed by cross-validation of the near infrared (NIR) cameras against each other, with thermal IR cameras, and with the beryllium evaporator, which lead to successful protection of the JET first wall during the last campaign. The operation temperature ranges of NIR protection cameras for the materials used on JET are Be 650-1600• C, W coating 600-1320• C, and W 650-1500

Real-time protection of the JET ITER-like wall based on near infrared imaging diagnostic systems

“…We used the fact that the MARFE provides strong continuum radiation in the NIR range with an excellent toroidal symmetry. The "virtual" temperatures delivered by JET-ILW wide-angle cameras are consistent within 4%, confirming the reliability of the in-vessel calibration (see Fig.12b) [37]. The cross-validation NIR cameras observing the beryllium evaporator, equipped with a thermocouple, also demonstrate a good agreement within 20°C at Tsurf=900°C.…”

“…Be 700-1400°C; W coating 700-1370°C; W 700-1400°C. The detailed description of the invessel calibration of the protection imaging system can be found in [37].…”

Effect of reflections on 2D tomographic reconstructions of filtered cameras and on interpreting spectroscopic measurements in the JET ITER-like wall divertor

“…1. The cameras are calibrated using the in-vessel calibration light source (ICLS) setup of JET, [12][13][14] providing reference data for spectroscopic analysis in absolute units of intensity.…”

Analysis of the outer divertor hot spot activity in the protection video camera recordings at JET

“…The aim of these correspondence criteria is to enable the recognition of the same hot spot in different frames of the video recording, in which the image of the hot spot does not always result in the same cluster of bright pixels due to fluctuations in its temperature or noise (e.g. bright pixels due to neutrons [6]).…”

“…In order to prevent recrystallization of the bulk W tile, and the delamination of the W coatings, the surface temperature must be kept below 1200 °C [3,4]. To prevent such damage to the plasma facing components (PFCs) due to excessive heat loads, JET relies on an array of video cameras, protection cameras, which monitor the temperature of the plasma facing surfaces [5][6][7][8]. The field of view of each protection camera is split into pre-determined regions of interest (ROIs).…”