Modelling of dust generation, transport and remobilization in full-metal fusion reactors

The design, licensing and operation of magnetic confinement fusion reactors impose various limitations on the amount of metallic dust particles residing inside the plasma chamber. In this context, predictive studies of dust production and migration constitute one of the main sources of relevant data. These are mainly conducted using dust transport codes, which rely on coupled dust-plasma and dust-wall interaction models, and require external input on the dust and droplet initial conditions. Some particularities of dust modelling in reactor-relevant conditions are analyzed with an emphasis on dust generation mechanisms relevant for disruption scenarios and on dust remobilization mechanisms relevant for ramp-up scenarios. Emerging topics such as dust production by runaway electron impact and pre-plasma remobilization of magnetic dust are also discussed.

Achievements of Actively Controlled Divertor Detachment Compatible with Sustained High Confinement Core in DIII-D and EAST

The compatibility of efficient divertor detachment with high-performance core plasma is vital to the development of magnetically controlled fusion energy. The joint research on the EAST and DIII-D tokamaks demonstrates successful integration of divertor detachment with excellent core plasma confinement quality, a milestone towards solving the critical Plasma-wall-interaction (PWI) issue and core-edge integration for ITER and future reactors. In EAST, actively controlled partial detachment with Tet,div ~ 5 eV around the strike point and H98 > 1 in different H-mode scenarios including the high βP H-mode scenario have been achieved with ITER-like tungsten divertor, by optimizing the detachment access condition and performing detailed experiments for core-edge integration. For active long pulse detachment feedback control, a 30s H-mode operation with detachment-control duration being 25s has been successfully achieved in EAST. DIII-D has achieved actively controlled fully detached divertor with low plasma electron temperature (Tet,div ≤ 5 eV across the entire divertor target) and low particle flux (degree of detachment, DoD >3), simultaneously with very high core performance (βN ~3, βP >2 and H98~1.5) in the high βP scenario being developed for ITER and future reactors. The high-βP high confinement scenario is characterized by an internal transport barrier (ITB) at large radius and a weak edge transport barrier (ETB, or pedestal), which are synergistically self-organized. Both the high-βP scenario and impurity seeding facilitate divertor detachment. The detachment access leads to the reduction of ETB, which facilitates the development of an even stronger ITB at large radius in the high βP scenario. Thus, this strong large radius ITB enables the core confinement improvement during detachment. These significant joint DIII-D and EAST advances on the compatibility of high confinement core and detached divertor show a great potential for achieving a high-performance core plasma suitable for long pulse operation of fusion reactors with controllable steady-state PWIs.

Development of a wall jet model dedicated to 1D combustion modelling for CI engines

Diesel engines are becoming smaller as technology advances, which means that the fuel spray (or jet) interacts with the cylinder walls before combustion starts. Most fuel injection 1D models (especially for diesel fuel) do not consider this interaction. Therefore, a wall-jet sub-model was created on an Eulerian 1D diesel spray model. It was calibrated using data from the literature and validated with experimental data from a fuel spray impacting a plate in a constant volume combustion chamber. Results show that the spray moving along the wall has a higher mixing rate but less penetration as an equivalent free jet, therefore they show a similar volume. Spray-wall interaction creates a stagnation zone right before the impact with the wall, and friction of the jet with the wall is relatively low. All these phenomena are well captured by the wall-jet sub-model.

Directional manipulation of diffusio-osmosis flow by design of solute-wall and solvent-wall interactions

Understanding of the diffusio-osmosis, the flow induced by a solute gradient acting in narrow interfacial layers at nanoscale solid-liquid interface, is of great value in view of the increasing importance of micro- and nano-fluidic devices and self-propelling particle. Here, using molecular dynamics simulations, we develop a numerical method for direct simulation of diffusio-osmosis flows mimicking the realistic experiment without any assumed external forces. It allows us to obtain reliable flow details which is however hard to get in experiments. We found that the solvent-wall interaction, previously overlooked in classical paradigm, plays a critical role in diffusio-osmosis process. In particular, diffusio-osmosis is controlled by the interaction difference between solute-wall and solvent-wall. When solute-than solvent-wall, a surface excess (depletion) of solute particles on solid-liquid interface is formed which induces diffusio-osmosis flow towards low (high) concentration. We modified the classical Derjaguin expression to include the effect of nanoscale hydrodynamics boundary conditions for the accurate prediction of diffusio-osmosis characteristics. Overall, our results provide the clear guidance for controlling fluids flow and manipulating motion of colloids under tunable solute concentrations.