A lot of effort is invested in plasma edge diagnostic to understand the interaction between the plasma and the vessel’s inner surface. Besides traditionally efficient tools like electrical (Langmuir) probes, neutral particle analysers, infrared cameras and dedicated spectral measurements, new methods are being developed and used at JET. Among the most innovative and successful are the quartz microbalance monitors which permit the measurement of the minute erosion and deposition on wall materials. At JET, five Quartz Micro-Balances and five Rotating Collectors are installed in the divertor region to register material deposition. Thanks to these measurements we can rapidly progress towards better plasma configurations to produce lower wall erosion.
Wide-angle infrared cameras
Infrared cameras help undestand and quantify the heat distribution on the walls. A new state-of-the-art wide-angle infrared camera overviews the heat load on plasma-facing components and to estimate their temperature during experiments.The system is expecially important for the protection of the ITER-Like Wall, which was installed on JET in order to resemble ITER-like conditions.
AT JET, eleven CCD cameras view different areas of the plasma facing surfaces using the near-infrared part of the spectrum to monitor for hot spots and to trigger appropriate actions. In the image from each camera, ‘regions of interest’ – i.e. ‘main chamber’, ‘divertor’ and ‘RF antennae’ – can be configured to offer protection from different events. The analysed information from each region of interest is sent to a system called the “Vessel Thermal Map” (VTM). VTM is programmed to identify the action that is required to prevent further heating of hot spots and to terminate heating in an intelligent way.