Infrared Thermography of Divertor ELM Heat Loads on TCV

Edge Localised Mode (ELM)-induced heat loads, in particular divertor heat loads present one of the main challenges in adopting nuclear fusion as an industrial-scale energy source. At present, the type-I ELMy plasma regime is chosen as the most suitable operational scenario because of its energy confinement and steady-state capabilities, however, with the understanding that the enormous quasi-periodic heat loads deposited by the ELMs will need to be controlled in order to avoid intolerable damage to heat- bearing elements. At present, a detailed theoretical understanding, and in particular, a sufficiently reliable way of predicting ELM behaviour based on basic discharge parameters is missing. The fusion community has been expending a great deal of effort in order to improve this situation by gathering as much experimental data as possible from a range of different-sized tokamaks, in order to develop empirical scalings and refine theoretical models, with the ultimate aim of mitigating their destructive power below thresholds where they won’t affect continuous scientific exploitation of the reactors. This experimental thesis joins into this effort via the installation and commissioning of a fast infrared camera on TCV viewing the outer divertor. Near the end of the thesis, an effort of similar magnitude has been carried out with a camera on temporary loan from the MAST group, in order to image the inner divertor region as well. The cameras possess a sub-array recording capability, enabling acquisition frequencies up to 25 kHz. Both cameras were calibrated with the combination of a low- and high-temperature blackbody source with large and small radiation surfaces, respectively. By estimating the surface emissivity as 0.85 and employing a gray-body model, target surface temperatures could be inferred. The resulting images were processed to produce 1D poloidal temperature profiles serving as an input to the THEODOR (THermal Energy Onto DivertOR) 2D finite-element code, with the goal of calculating the heat fluxes impinging on plasma facing components. The VIR (Vertical InfraRed) outer divertor system images a flat, horizontal surface covered by relatively large tiles from a perpendicular viewing angle. Deposited layers, microscopic surface changes and very small dust particles cause the appearance of microscopic hot-spots in the field-of-view (FOV), leading to a substantial deviation from the assumed model of a single-temperature (the tile bulk graphite) gray body radiator. Near the middle of the thesis, nearly all tiles inside TCV have been removed for cleaning via sandblasting. With 3 of the tiles having been left untouched, this presented a good opportunity to contrast the behaviour of the cleaned and uncleaned (~12 years of operation) surfaces. It has been found that already after 10 days of operation, the temperature signal significantly exceeds what could be expected from a pure graphite surface. This, though increasing error bars of the final he