Samenvatting

The purpose of this report is to assess the relevance of the measurement of the spectrally resolved distribution of radiation in tokamak boundary plasmas. This assessment is important and urgent in view of the recent ambition to design and construct a multi-camera configuration for hyper imaging spectroscopy1 in the TCV tokamak in Lausanne, Switzerland. A collection of videos recorded in the visible light range { sometimes with a C-III filter { from earlier research was used and compared to single line of sight spectroscopic data and measurements from Langmuir probes.
The videos have been recorded with a high frame rate camera that was applied for plasma boundary detection and for real time plasma position control. The first step in project was to index the videos in a database, which is driven by SQL { this provides superior exibility and speed over a spreadsheet. Various phenomena were identified in which a clear variation in the distribution of the intensity over the plasma can be observed. Then, a list containing the IDs of the recordings was constructed from the database so that sufficient review material was available for each phenomenon. Four phenomena were identified as potential study cases. These are a) data from two cameras one of which is using a C-III filter while the other is observing visible light are used to identify a significant spatial displacement of the hydrogen and carbon lines. b) Emitting structures in the plasma boundary, reminiscent of MARFEs [1], have been observed. c) Quasi-toroidal variations in the intensity are observed, reminiscent of the effects of micro-turbulence. d) During some discharges, plasma detachment is thought to be observed by a variation in intensity that shifts over a leg towards the divertor.
Examples of these phenomena will be shown in the report. For further analysis { given the availability of the data at TCV { it was decided to proceed with the C-III data and the alleged detachment data for further analysis.
The temperature was estimated based on the assumption that the temperature of the plasma boundary is the same as the photon temperature of their main contributing emission component. With MATLAB image processing, the distance between the apparent boundaries of C-III and H?radiation have been estimated. With those results, the spatial (rTx = 0:77 eV m?1) gradient and the temporal evolution thereof has been estimated.
For the alleged detachment cases, a detailed comparison with measurements of additional diagnostics was carried out. Langmuir probe data shows sudden changes in the saturation current to the divertor and the perpendicular power load on the divertor surface. This coincides with a reduced heat- and particle
load. It can be concluded that detachment is occurring and that the heat load is reduced. Spectrally resolved data shows that the instant that the plasma detaches from the divertor, the spectral intensities change as well. Spectral, spatial and temporal solutions can thus be found for this phenomenon.
The progress of this work was hampered due to a mismatch of ID numbers of the discharges or due to saturated signals from the Langmuir probes in some cases. This was solved by combining data from different yet similar discharges. With this caveat, it is demonstrated that temporal, spectral and spatial data is crucial to understand and -most likely - control the plasma boundary.