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Abstract: Heat deposition onto plasma facing components outside the divertor by ELMs and fast particles has been investigated in ASDEX Upgrade. Heat fluxes up to tens of megawatts per square meter are found during ELMs on limiters and a few megawatts per square meter in between. The total deposited power on non-divertor structures can be up to 10% of the heating power and has to be considered for high power next step experiments. The mechanisms behind the observed heat load patterns are qualitatively understood. The main contributions come from fast ions created by neutral beam injection (and ion cyclotron minority) heating, and from ELMy energy bursts from the plasma edge. [Copyright &y& Elsevier]

An observation system using fast digital cameras was developed to measure a cryogenic hydrogen pellet’s cloud structure, trajectory, and velocity changes during its ablation in ASDEX Upgrade plasmas. In this article the system, the applied numerical methods, and the results are presented. The three-dimensional pellet trajectory and velocity components were reconstructed from images of observations from two different directions. Pellet acceleration both in the radial and toroidal directions was detected. The pellet cloud distribution was measured with high spatio-temporal resolution. The cloud surrounding the pellet was found to be elongated along the magnetic field lines. Its typical size is 5–7 cm along the field lines and 2 cm in the perpendicular directions. A cloud extension in the poloidal direction was also observed which may be related to the drift of the detached part of the cloud. [ABSTRACT FROM AUTHOR]

Microwave reflectometry has been proposed as an alternative/backup approach to the usual magnetic systems in long pulse operation on the International Thermonuclear Experimental Reactor (ITER) for plasma position and shape control. This new application of reflectometry must be fully demonstrated in present machines in view of its importance for ITER. First experiments performed in ASDEX Upgrade with frequency modulated continuous wave with reflectometry diagnostic showed that radial variations of the plasma column occurring during preprogrammed horizontal as well as vertical plasma displacements could be followed with sufficient accuracy (≤1 cm) in phases with approximately constant density. In this article we determine the plasma edge position simultaneously in the inner and outer midplane, of ohmic L-mode density limit and ELMy H-mode discharges in ASDEX Upgrade, both with significant density variations. It is shown that if normalized density layers are selected, at a certain percentage of the average line density, the results from reflectometry are in good agreement with the corresponding data, separatrix position, derived from the magnetics. Further work aiming at the full demonstration of plasma position and shape measurements from reflectometry is discussed. [ABSTRACT FROM AUTHOR]

Abstract: ASDEX Upgrade pursues the progressive increase of W coated plasma facing components. At present, the central column, the upper passive stabiliser loop, the complete upper divertor, the baffles at the lower divertor, as well as six tiles of one guard limiter at the low field side are W coated, representing about 65% of the total surface area. W erosion at these guard limiter tiles exceeds the erosion found at other main chamber components by more than one order of magnitude, and spectroscopically determined erosion yields indicate a strong contribution from fast particles. Upper single null discharges do not show an obviously increased W content compared to discharges run in the lower C based divertor. [Copyright &y& Elsevier]

Abstract: A comparative analysis of the spatial and temporal characteristics of transient energy loads (ELMs and disruptions) on plasma facing components (PFCs) in present tokamak devices and their extrapolation to next step devices is presented. Type I ELMs lead to the expulsion of energy by the plasma in helical structures with ballooning-like features and toroidal numbers in the range n =10–15. The plasma energy is transported towards the divertor and the main chamber PFCs leading to significant transient energy loads at these two locations on small wetted area. The largest transient energy fluxes onto PFCs in tokamaks are measured during the thermal quench of disruptions. These fluxes do not exceed greatly those of large Type I ELMs, due to the much larger wetted area for energy flux during the thermal quench compared to Type I ELMs. The implications of these findings for the next step devices are discussed. [Copyright &y& Elsevier]