Calculation and experimental investigation of fusion reactor divertor plate and first wall protection by capillary-pore systems with lithium

Liquid metals such as gallium, tin and lithium are potential plasma-facing materials that may be used to withstand the high heat and particle fluxes in a fusion plasma environment. The interaction of plasma with liquid gallium surfaces has been examined experimentally because of the liquid’s wide temperature range (303–2478 K) and relatively low chemical reactivity. The deuterium retention in liquid gallium samples following plasma exposure in the PISCES experimental plasma device is measured using thermal desorption spectroscopy and is found to be independent of exposure temperature. The retention level saturates at a value of roughly 3 × 10 23 Dm −3 (or about 5 ppm) for sample exposure temperatures ranging from 333 to 800 K and incident ion fluences up to 1.5 × 10 26 Dm −2 . Results from the analyses of the surface after plasma exposure using Auger electron spectroscopy is reported. Micropitting is observed in scanning electron microscope pictures taken after plasma exposure and after resolidification of the gallium surface. Calculations based on the observed retained concentration of deuterium in gallium show that the pumping capabilities of a flowing gallium surface will be small. In addition, measurements of the erosion yield of deuterium-bombarded gallium are presented and compare favourably with results from sputtering yield calculations.

https://iopscience.iop.org/article/10.1088/0029-5515/42/9/303/pdf

Deuterium plasma interactions with liquid gallium

The Fusion Energy System Studies (FESS) Fusion Nuclear Science Facility (FNSF) project team in the United States is examining the use of liquid metals (LMs) for plasma-facing components (PFCs). Our...

Integrated Liquid Metal Flowing First Wall and Open-Surface Divertor for Fusion Nuclear Science Facility: Concept, Design, and Analysis

In the framework of fusion energy research based on magnetic confinement, pulsed high-field tokamaks such as Alcator and FTU have made significant scientific contributions, while several others have been designed to reach ignition, but not built yet (IGNITOR, FIRE). Equivalent stellarator concepts, however, have barely been explored. The present study aims at filling this gap by: (1) performing an initial exploration of parameters relevant to ignition and of the difficulties for a high-field stellarator approach, and, (2) proposing a preliminary high-field stellarator concept for physics studies of burning plasmas and, possibly, ignition. To minimize costs, the device is pulsed, adopts resistive coils and has no blankets. Scaling laws are used to estimate the minimum field needed for ignition, fusion power and other plasma parameters. Analytical expressions and finite-element calculations are used to estimate approximate heat loads on the divertors, coil power consumption, and mechanical stresses as functions of the plasma volume, under wide-ranging parameters. Based on these studies, and on assumptions on the enhancement-factor of the energy confinement time and the achievable plasma beta, it is estimated that a stellarator of magnetic field B ~ 10 T and 30 m3 plasma volume could approach or reach ignition, without encountering unsurmountable thermal or mechanical difficulties. The preliminary conceptual device is characterised by massive copper coils of variable cross-section, detachable periods, and a lithium wall and divertor.

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Initial Exploration of High-Field Pulsed Stellarator Approach to Ignition Experiments

The liquid metal film Plasma Facing Component (PFC) has been considered as one of the most promising ways to realize a long time working PFC. However, due to the existence of a magnetic field, the magnetohydrodynamic effects appearing in the liquid metal film flow directly influence the reliability of the flowing liquid metal limiter or divertor. In the present study, considering the influence of the flow rate, the transverse magnetic field and the inclination angle, we carry out experiments on the liquid metal film flowing along an inclined conducting stainless steel plate. The Laser Profilometer(LP), as well as the high-speed camera are respectively adopted to obtain the local film thickness quantitatively and free surface structures qualitatively. We observe the magnetohydrodynamic effects of liquid metal film flow, such as the nonmonotonic change of film thickness, the reduction of film flow velocity and the weakening of free surface waves in the direction of magnetic lines. Moreover, the film thickness increases with an increasing flow rate, while decreases with an increasing inclination angle at a constant value of the magnetic field. While plotting the relative film thickening $\delta_{en}$ and the reduction of flow velocity against the Stuart number $N$, we find that there is a critical $N$, $N_{cr}\approx0.1$, at which $\delta_{en}$ starts increasing dramatically. The $\delta_{en}$sin$\beta$, from all of the experimental data, collapses onto one line, which can be scaled as $\delta_{en}$sin$\beta$ $\sim N$. The present experimental data and its scaling law are useful to estimate the magnetohydrodynamic effects on liquid metal film flows while designing the liquid metal film PFC.

V.N. Demjanenko

Papers

Research and development of liquid metal systems for a tokamak reactor