Optimization of pumping efficiency and divertor operation in DEMO

In the present work a sensitivity analysis of the pumping performance of a standard divertor design for two extreme dome cases (with and without) and different pumping port locations is performed. Such an investigation re-assesses the role of the divertor dome in the design of a DEMO divertor cassette. The non-linear neutral gas flow in the private flux and sub-divertor region is modeled based on the Direct Simulation Monte Carlo (DSMC) method, which takes into account the intermolecular collisions as well as the interaction of the molecules with the stationary walls. For this specific configuration, three different pumping port locations, namely in the low and high field bottom sides of the sub-divertor and directly under the dome haven been chosen. It is shown that the optimum pumping port location is found to be directly under the dome, since the pumped particle flux is increased by a factor 2–3 compared to the one, where the port is located inside the low and high field side divertor “shoulders”, respectively. In addition, the divertor dome physically restricts the conductance between the private flux region and the main chamber, enabling the compression of the neutral gas. However, the dome has no direct influence on the macroscopic parameters as the number density and the temperature at the pumping port. Furthermore, it is shown that without the dome, a strong outflux of neutrals towards the plasma core and through the x-point and its vicinity can be expected. This outflux can be reduced by a factor of 2 by positioning the pumping port directly under the dome. Finally it is noted that in all the obtained calculations, the flow field remains homogeneous without the presence of vortices. This can be explained by the fact that the studied geometry does not include any high curvature surfaces, which promote the formation of such flow structures

Effect of design geometry of the demo first wall on the plasma heat load

In this work we analyse the effect of W armour surface shaping on the heat load on the W/EUROFER DEMO sandwich type first wall blanket module with the water coolant. The armour wetted area is varied by changing the inclination and height of the «roof» type armor surface. The deleterious effect of leading edge at the tiles corner caused by misalignment is replaced in current design by rounded corners. Analysis has been carried out by means of the MEMOS code to assess the influence of the thickness of the layers and effect of the magnetic field inclination. Calculations show the evolution of the maximum temperatures in the tungsten, EUROFER, Cu allow and the stainless-steel water tube for different level of surface inclination (chamfering) and in the case of rounded corners used in the current design. It is shown that the blanket module materials remain within a proper temperature range only at shallow incident angle if the width of EUROFER is reduced at list twice compare with the reference case

Matter Injection in EU-DEMO: The Preconceptual Design

EU-DEMO will be the next step in Europe after ITER on the path toward a fusion power plant. The matter injection systems have to provide the requested material in order to establish, maintain, and terminate the burning plasma. Their main function is to fuel the plasma, but other tasks are addressed as well like delivering matter for generating sufficient core radiation and divertor buffering. In the preconceptual design phase performed from 2014 to 2020, the matter injection systems, in particular pellet injection and gas injection, have been assessed. This work describes the main findings and state of the art of the matter injection systems at the transition from the preconceptual design phase to the conceptual design phase