No abstract

The Magnum-PSI facility is available for plasma-material interaction studies. • Magnum-PSI is capable to reach relevant plasma parameters for the ITER divertor. • Particle fluxes over 10 25 m-2 s-1 and heat fluxes of up to 50 MWm-2 are obtained. • Particle fluences of up to 10 30 particles m-2 have been achieved. • Linear regression and artificial neural network analysis have been applied.

In magnetic confinement thermonuclear fusion the exhaust of heat and particles from the core remains a major challenge. Heat and particles leaving the core are transported via open magnetic field lines to a region of the reactor wall, called the divertor. Unabated, the heat and particle fluxes may become intolerable and damage the divertor. Controlled ‘plasma detachment’, a regime characterized by both a large reduction in plasma pressure and temperature at the divertor target, is required to reduce fluxes onto the divertor. Here we report a systematic approach towards achieving this critical need through feedback control of impurity emission front locations and its experimental demonstration. Our approach comprises a combination of real-time plasma diagnostic utilization, dynamic characterization of the plasma in proximity to the divertor, and efficient, reliable offline feedback controller design.

The oxygen evolution reaction (OER) has been identified as one of the performance-limiting processes in solar water splitting using photoelectrochemical (PEC) cells. One of the reasons for the low OER performance is related to the existence of different types of surface states at the semiconductor–electrolyte interface: recombining surface states (r-SS) and surface states due to intermediate species (i-SS). Since the impact of surface states on OER is still under debate, we investigate how different types of surface states affect PEC water oxidation and how they impact experimental measurements. In a new computational approach, we combine a microkinetic model of the OER on the semiconductor surface with the charge carrier dynamics within the semiconductor. The impact of r-SS and i-SS on the current–voltage curves, hole flux, surface state capacitance, Mott–Schottky plots, and chopped light measurements is systematically investigated. It is found that (a) r-SS results in a capacitance peak below the OER onset potential, while i-SS results in a capacitance peak around the onset potential; (b) r-SS leads to an increase in the OER onset potential and a decrease in the saturation current density; (c) r-SS leads to Fermi-level pinning before the onset potential, while i-SS does not result in Fermi-level pinning; and (d) a smaller capacitance peak of i-SS can be an indication of the lower catalytic performance of the semiconductor surface. Our approach in combination with experimental comparison allows distinguishing the impact of r-SS and i-SS in PEC experiments. We conclude that r-SS reduces the OER performance and i-SS mediates the OER.

This paper presents DIV1D, a new 1D dynamic physics-based model of the divertor plasma under development to study and control the dynamics of detached plasmas. An innovative feature of DIV1D is that it mimics cross-field transport using an effective flux expansion and includes a neutral gas background outside the divertor leg. We outline a 1D mapping procedure for static 2D SOLPS-ITER simulations of divertor plasmas in the Tokamak à Configuration Variable (TCV) which can be used to benchmark 1D codes. For DIV1D good agreement is found for the most important divertor plasma quantities along the leg (e.g. densities, temperature, heat flux, and velocity) both in qualitative and quantitative sense. In addition, the comparison with SOLPS-ITER demonstrates that DIV1D self-consistently captures the evolution of divertor plasma quantities in the main heat flux channel as function of the upstream plasma density in a scan from 2 to 3 · 1019 m−3. The agreement is ascribed to the unique account of cross-field transport in DIV1D with an effective flux expansion and the interaction with an external neutral gas background

The EUROfusion MST1 team * , and the TCV team †

No abstract

The tokamak à configuration variable (TCV) continues to leverage its unique shaping capabilities, flexible heating systems and modern control system to address critical issues in preparation for ITER and a fusion power plant. For the 2019–20 campaign its configurational flexibility has been enhanced with the installation of removable divertor gas baffles, its diagnostic capabilities with an extensive set of upgrades and its heating systems with new dual frequency gyrotrons. The gas baffles reduce coupling between the divertor and the main chamber and allow for detailed investigations on the role of fuelling in general and, together with upgraded boundary diagnostics, test divertor and edge models in particular. The increased heating capabilities broaden the operational regime to include T e/T i ∼ 1 and have stimulated refocussing studies from L-mode to H-mode across a range of research topics. ITER baseline parameters were reached in type-I ELMy H-modes and alternative regimes with ‘small’ (or no) ELMs explored. Most prominently, negative triangularity was investigated in detail and confirmed as an attractive scenario with H-mode level core confinement but an L-mode edge. Emphasis was also placed on control, where an increased number of observers, actuators and control solutions became available and are now integrated into a generic control framework as will be needed in future devices. The quantity and quality of results of the 2019–20 TCV campaign are a testament to its successful integration within the European research effort alongside a vibrant domestic programme and international collaborations.