Liquid Metal Plasma-facing Components Research Articles

Recent progress in the development of liquid metal plasma facing components for magnetic fusion devices

One of the most critical challenges for future fusion reactors is to develop longevity plasma-facing components (PFCs) exposed to extremely high heat and neutron loads. As opposed to those employing solid metals, PFCs with flowing liquid metals (LM) have shown self-healing, heat removal and good impurity control capabilities, all essential to fusion devices. Recently, significant progress in LM-PFC development has been reported globally, with data from several magnetic fusion devices. These studies reveal that LM-PFCs can endure extreme heat fluxes while maintaining plasma compatibility. New design concepts have been proposed and numerically analyzed, advancing models for liquid PFCs in future reactors. Despite existing technical challenges, these developments suggest that LM-PFCs hold promise for future fusion applications.

Coupled model for liquid lithium plasma facing components

Numerical analysis provides the design choice and operating window of liquid metal Plasma Facing Components (PFC) concepts. Coupled analysis of boundary plasma together with the surrounding boundary structures is required. To achieve this goal, PPPL is developing a comprehensive multi-physics model for modeling of PFCs in fusion devices. The model includes the fluid-kinetic code SOLPS-ITER and the flow and heat transfer code CFX from ANSYS. SOLPS-ITER was augmented with a liquid metal boundary condition algorithm, allowing direct two-way coupling of the plasma analysis with the two-dimensional analytical slab flow model which includes heat convection in the liquid metal PFC. The target heat flux resulting from this coupled analysis is used as a boundary condition for detailed 3D Computational Fluid Dynamics (CFD) Magneto Hydro Dynamics (MHD) and heat transfer analysis. A new formulation of MHD equations is introduced in the numerical procedure ensuring current conservation of the discretized equations. Results of the 3D analysis are used for final validation of the coupled model. A PFC design where a porous wall is used to stabilize the liquid metal surface, while MHD drive is used to push the liquid metal flow inside the PFC, will be investigated in the regimes where vapor shielding is created for enhanced volumetric plasma heat dissipation.

Conference Report on the 7th International Symposium on Liquid metals Applications for fusion (ISLA-7)

Supported by the world magnetic fusion research community, a series of International Symposia on Liquid metals Applications for fusion (ISLA) have been held biannually since 2010. The 7th edition (ISLA-7) was held for the period from 12 December through 16 December 2022, at Chubu University located in Kasugai, Aichi, Japan. For the first time in the history of this series of symposia, ISLA-7 was held in a hybrid fashion, due to the COVID-19 situation. The total number of the participants was 60, 34 out of whom attended the symposium in person, and the rest participated online. As to the presentation statistics, 29 papers were presented in person, whereas 21 presentations were delivered online but real-time by the presenters in China, Spain, the UK, and the USA. Both of the presentations delivered in person and online were recorded, and the video has been shared by all participants. These participants represent 11 countries: China, Czech, Italy, Japan, Latvia, Netherlands, Russia, Thailand, the UK, and the USA. All these numbers are among the largest in this series of symposia. Covered by these presentations are; in session-2, program overviews and liquid metal research review; in session-3, liquid metal flows, and MHD issues; in session-4, liquid metal facilities; in sessions-5 and 6, liquid metal experiments and modeling; in session-7, divertor physics and heat flux mitigation; in session-8, plasma and liquid metals interactions; in session-9 liquid metal plasma-facing components, erosion, and wettability. In addition, there were an opening session whereby several opening addresses were delivered and also a closing session where all technical session summaries were presented by the respective session chairs.

Magnetohydrodynamics in free surface liquid metal flow relevant to plasma-facing components

While flowing Liquid Metal (LM) Plasma-Facing Components (PFCs) represent a potentially transformative technology to enable long-pulse operation with high-power exhaust for fusion reactors, Magnetohydrodynamic (MHD) drag in the conducting LM will reduce the flow speed. Experiments have been completed in the linear open-channel LMX-U device [Hvasta et al 2018 Nucl. Fusion 58 01602] for validation of MHD drag calculations with either insulating or conducting walls, with codes similar to those used to design flowing LM PFCs for a Fusion Nuclear Science Facility [Kessel et al 2019 Fusion Sci. Technol. 75 886]. We observe that the average channel flow speed decreased with the use of conducting walls and the strength of the applied transverse magnetic field. The MHD drag from the retarding Lorentz force resulted in an increase of the LM depth in the channel that ‘piled up’ near the inlet, but not the outlet. As reproduced by OpenFOAM and ANSYS CFX calculations, the magnitude and characteristics of the pileup in the flow direction increased with the applied traverse magnetic field by up to 120%, as compared to the case without an applied magnetic field, corresponding to an average velocity reduction of ∼45%. Particle tracking measurements confirmed a predicted shear in the flow speed, with the surface velocity increasing by 300%, despite the 45% drop in the average bulk speed. The MHD effect makes the bulk flow laminarized but keeps surface waves aligned along the magnetic field lines due to the anisotropy of MHD drag. The 3D fringe field and high surface velocity generate ripples around the outlet region. It was also confirmed that the MHD drag strongly depends on the conductivity of the channel walls, magnetic field, and volumetric flow rate, in agreement with the simulations and a developed analytical model. These validated models are now available to begin to determine the conditions under which the ideal LM channel design of a constant flow speed and fluid depth could be attained.

Numerical Analysis of Liquid Metal MHD Flow and Heat Transfer for Open-Surface Li Divertor in FNSF

Within the ongoing U.S.-based program on the development of liquid metal plasma-facing components, numerical simulations and analyses are performed to address the feasibility of the open-surface Li divertor. In the previous scoping studies (Smolentsev, 2021), heat-removal capabilities of the divertor were assessed using a simplified flow model for a slug-type velocity profile and constant flow thickness. Here, new analyses take into account forces acting on the flowing Li layer. Three reduced-order mathematical models are applied under the conditions of the U.S. Fusion Nuclear Science Facility (FNSF) to access magnetohydrodynamic (MHD) flow development effects, velocity distribution, and surface waves: 1) fully developed MHD flow; 2) quasi-2-D developing MHD flow; and 3) multiphase MHD flow. The obtained results for MHD flows and the surface heat flux computed with the plasma code scrape-off layer plasma simulation for ITER (SOLPS-ITER) are then used as input data to compute the temperature distribution in the divertor by solving the convection–diffusion energy equation.

HIDRA-MAT liquid metal droplet injector for liquid metal applications in HIDRA

A liquid metal droplet injector was explicitly designed for the Hybrid Illinois Device for Research and Applications Material Analysis Test-stand (HIDRA-MAT) at the University of Illinois Urbana-Champaign to prepare liquid metal plasma-facing components (PFCs) for plasma exposure. The design goals were to create a compact, reliable, and robust design that could apply liquid metal droplets in-vacuo to a variety of samples. The injector was designed for liquid metal use, and results discussed pertain to lithium. The injector can produce lithium droplets of consistent size by utilizing programmable piston movement. Droplet formation data is presented for four different piston step sizes (0.125 mm, 0.25 mm, 0.5 mm, and 1 mm) at three different nozzle temperatures (185 °C, 230 °C, and 270 °C). Droplets are formed on the injector nozzle tip and a linear shift mechanism vertically translates the droplet to the substrate for application. This design prevents the droplet from inadvertently detaching off the nozzle and falling to the sample. Application of the liquid metal droplet ensures placement consistency on the substrate and helps avoid damage to components in HIDRA-MAT that should not interact with liquid metals. A description of the liquid lithium droplet creation and application results is given and provides additional insight into the cooling and oxidation of lithium droplets under vacuum conditions. A second nozzle was fabricated and demonstrated repeatability in droplet diameter creation having a variance of ±0.14 mm for droplets created from the same number of piston steps. The end-use for the injector on HIDRA-MAT is to apply liquid metals to PFCs and expose them to HIDRA's plasma with subsequent intershot in-vacuo surface analysis in HIDRA-MAT for plasma-material interaction studies.

Developing solid-surface plasma facing components for pilot plants and reactors with replenishable wall claddings and continuous surface conditioning. Part A: concepts and questions

It is estimated that pilot plants and reactors may experience rates of net erosion and deposition of solid plasma facing component (PFC) material of 103–105 kg yr−1. Even if the net erosion (wear) problem can be solved, the redeposition of so much material has the potential for major interference with operation, including disruptions due to so-called ‘unidentified flying objects (UFOs)’ and unsafe dust levels. The potential implications appear to be no less serious than for plasma contact with the divertor target: a dust explosion or a major UFO-disruption could be as damaging for an actively-cooled deuterium-tritium (DT) tokamak as target failure. It will therefore be necessary to manage material deposits to prevent their fouling operation. This situation appears to require a fundamental paradigm shift with regard to meeting the challenge of taming the plasma–material interface: it appears that any acceptable solid PFC material will in effect be flow-through, like liquid–metal PFCs, although at far lower mass flow rates. Solid PFC material will have to be treated as a consumable, like brake pads in cars. ITER will use high-Z (tungsten) armor on the divertor targets and low-Z (beryllium) on the main walls. The ARIES-AT reactor design calls for a similar arrangement, but with SiC cladding on the main walls. Non-metallic low-Z refractory materials such as ceramics (graphite, SiC, etc) used as in situ replenishable, relatively thin—of order mm—claddings on a substrate which is resistant to neutron damage could provide a potential solution for the main walls, while reducing the risk of degrading the confined plasma. Separately, wall conditioning has proven essential for achieving high performance. For DT devices, however, standard methods appear to be unworkable, but recently powder droppers injecting low-Z material ∼continuously into discharges have been quite effective and may be usable in DT devices as well. The resulting massive generation of low-Z debris, however, has the same potential to seriously disrupt operation as noted above. Powder droppers provide a unique opportunity to carry out controlled studies on the management of low-Z slag in all current tokamaks, independent of whether their protection tiles use low-Z or high-Z material.

Liquid metal “divertorlets” concept for fusion reactors

Abstract A new, novel approach to liquid metal plasma facing components called “divertorlets” is presented and accompanied by experiments, simulations, and analysis. The development of a robust and reliable plasma facing component at the divertor is ongoing, with liquid metal divertor concepts gaining interest by showing promise for being able to handle higher heat fluxes as well as improve plasma performance through a reduction in particle recycling. The presented design in this work seeks to address challenges associated with evaporation, operation power, and liquid metal inventory. Divertorlets utilize many adjacent narrow channels with alternating vertical velocity that maintain large flow rates with small velocities at the surface by minimizing the flow path length. Preliminary results using a test stand on LMX-U at PPPL and simulations in COMSOL demonstrate the successful operation and the potential for divertorlets to remove large heat fluxes, with projections made to reactor scale showing the expected system performance.

Exploration of Sn70Li30 alloy as possible material for flowing liquid metal plasma facing components

• First wetting data for Sn 70 Li 30 alloy are reported on 316 SS, Mo and W substrates. • Wetting temperatures of 360 °C, 390 °C and 405 °C were measured respectively. • Alloy contamination/passivation worsened wettability with Δ T~130 °C in worst cases. • First depth profile characterization of the tin-lithium alloy by SIMS-ToF was carried out. • Mixing boundaries between alloy and substrates studied by SEM/EDS and 3D microscopy. • Lithium and tin induced corrosion found on 316 SS exposed at T < 550 °C during t ≤ 3 h. • Molybdenum and tungsten presented good compatibility after equivalent interaction. As an advanced alternative to solid materials, Liquid Metals (LM) may offer more resilient and feasible Plasma Facing Components (PFCs). Particularly, regarding the unavoidable material erosion/degradation produced by particle/heat fluxes in future fusion devices where much longer duty cycles are expected. Furthermore, configurations that propose a flowing LM surface can add the advantage of a continuously fresh and clean layer facing the plasma. Although lithium is the most widely tested option, tin-lithium (SnLi) alloys have been proposed to attempt to combine the positive characteristics of both pure elements and ameliorate the specific issues of lithium. In this work, the potential use of Sn 70 Li 30 alloy in such flowing concepts has been explored by addressing several preliminary and mandatory aspects for its utilization. Key issues such as wettability and compatibility of the alloy with relevant substrates have been studied in a multidisciplinary approach. The data obtained from deposited liquid tin-lithium droplets indicates approximate wetting temperatures of 360 °C, 390 °C and 405 °C for the fresh alloy on 316 stainless steel, molybdenum, and tungsten, respectively. However, the alloy contamination appeared to strongly affect the wetting characteristics of materials, increasing their wetting temperature by ~130 °C in the worst observed cases. Interestingly, in some instances, the instability of the liquid alloy surface was observed in the form of sudden gaseous ejection. The deposited droplets were posteriorly characterized in terms of absolute composition and depth profile by Inductively Coupled Plasma-Optical Emission Spectroscopy (ICP-OES) and Secondary Ion Mass Spectrometry (SIMS-ToF). Additionally, the nature and composition of the boundaries between the substrates and alloy microparticles was investigated by Scanning Electron Microscopy (SEM), Energy Dispersive X-Ray Spectroscopy (EDS), and 3D Laser microscopy. The overall results of this post-mortem characterization revealed that first signs of corrosion induced by both alloy elements (lithium-chromium association and iron-tin intermetallic mixing) were present on 316 stainless steel after short exposures (≤3 h) at temperatures lower than 550 °C. Conversely, molybdenum and tungsten showed good compatibility with the alloy in equivalent conditions. The global implications of these results are finally addressed, focusing on the future perspectives and the more viable scenarios for the eventual utilization of these alloys in flowing liquid metal configurations.

Free-Surface Liquid Lithium Flow Modeling and Stability Analysis for Fusion Applications

Liquid metal plasma facing components are considered an attractive design choice for fusion devices including pilot plants. Virtual prototyping of such devices includes modeling of free-surface flow of the electrically conductive liquid, which requires computational fluid dynamics (CFD) and magnetohydrodynamics (MHD) simulations. Numerical tools capable of simulating flows and heat transfer in the free-surface MHD flow were developed at PPPL based on the customized ANSYS CFX. MHD is introduced using a magnetic vector potential approach. Free-surface flow capabilities are available in the code and were tested. Special stabilization procedures were derived and applied to improve convergence of the momentum equations with the source terms due to the Lorentz force and surface tension. Important characteristics of the fusion-relevant liquid metal flow is free surface smoothness and stability. Heat flux from the plasma impacts the liquid surface at a very acute angle, so any change of the free surface from axisymmetry can dramatically increase the local heat flux density and thus create excessive evaporation of liquid lithium into the plasma, which is detrimental to operations. Stability analysis of the liquid metal film flow was performed to determine applicable flow regimes. Thin film flow along horizontal wall is considered. Effects of gravity, magnetic field, and surface tension are included in the analysis.

A Domestic Program for Liquid Metal PFC Research in Fusion

While high-Z solid plasma-facing components (PFCs) are the leading candidates for reactors, it is unclear that they can survive the intense plasma material interaction (PMI). Liquid metals (LM) PFCs offer potential solutions since they are not susceptible to the same type of damage, and can be “self-healing”. Following the Fusion Energy System Study on Liquid Metal Plasma Facing Components study that recently was completed by Kessel et al. (Fusion Sci Technnol 75:886, 2019) a domestic LM PFC design program has been initiated to develop reactor-relevant LM PFC concepts. This program seeks to evaluate LM PFC concepts for a Fusion Nuclear Science Facility (FNSF) or a Compact Pilot Plant via engineering design calculations, modeling of PMI and PFC components and laboratory experiments. The latter involves experiments in dedicated test stands and confinement devices and seeks to identify and answer open questions in LM PFC design. The new national LM PFC program is first investigating lithium as the plasma facing material for a flowing divertor PFC concept. Several flow speeds will be evaluated, ranging from ~ cm/s to m/s. The surface temperature will initially be held below the strongly evaporative limit in the first design; higher temperatures with strong evaporation will be considered in future concepts. Other topics of interest include: understanding of the hydrogen and helium interaction with the liquid lithium; single effect experiments on wetting, compatibility and embrittlement; and prototypical experiments for control and characterization of flowing LM. A path to plasma and future tokamak exposure of these concepts will be developed.

Development of a new TZM substrate flowing liquid lithium limiter for high performance plasma discharge in EAST

Abstract Liquid metal plasma-facing components (PFCs) provide certain promising advantages as compared with solid PFCs. A new flowing liquid lithium (FLiLi) limiter using a Titanium-Zirconium-Molybdenum Alloy (TZM) material substrate was developed and inserted into H-mode plasmas in EAST. As compared to the previous FLiLi limiters that used a copper heat sink covered with a stainless steel (SS) protective coating, the TZM limiter has better erosion resistance and wettability. Also, helium-cooling and water-cooling simulations show acceptable performance under continuous 2 MW/m2 heat flux deposited on the plate for 10 s. Both simulations show a peak surface temperature located at the ends of the plate where the cooling tubes can’t quite reach just below 650℃ while ignoring the influence of Li flowing, evaporation, and vapor shielding. Moreover, FLiLi is introduced to plasma lead to lower recycling and slight storage energy of plasma increase.

Perspectives on the FESAC transformative enabling capabilities: Priorities, plans, and Status

• Perspectives are given on recent efforts in the United States on the five “Transformative Enabling Capabilities” identified in a 2018 FESAC report. These areas are: • Advanced algorithms. • High-critical-temperature superconductors. • Advanced materials and manufacturing. • Novel technologies for tritium fuel cycle control. • Fast flowing liquid metal plasma-facing components. In early 2017, the Fusion Energy Sciences Advisory Committee (FESAC), an advisory committee to the United States Department of Energy, was charged with identifying transformative enabling capabilities (TECs) “that could promote efficient advance toward fusion energy, building on burning plasma science and technology.” A subcommittee with broad expertise was formed and sought feedback from scientific experts, including experts from outside the fusion community. Three workshops were conducted, and a report was approved by FESAC in 2018 that identified four of the “most promising” TECs: advanced algorithms, high-critical-temperature superconductors, advanced materials and manufacturing, and novel technologies for tritium fuel cycle control. In addition, one “promising” TEC was identified: fast flowing liquid metal plasma-facing components. This paper will give details on the promising TECs and an overview on considerations of these TECs in the United States since the publication of the report.

Conference report on the 1st US–Japan workshop on power and particle control by liquid metal plasma-facing components in a steady state magnetic fusion DEMO reactor

As part of the US–Japan bilateral collaboration program, a new series of workshops have been inaugurated on the subject of ‘Power and Particle Control by Liquid Metal Plasma-Facing Components in a Steady State Magnetic Fusion DEMO Reactor’. The first workshop of this series was held at Princeton Plasma Physics Laboratory on 11–13 March 2019. This conference report is intended to share 24 technical presentations, discussion and the planning of future workshops with the world magnetic fusion community.

Design and Analysis of the Liquid Metal Free-Surface Divertor Cooling System

Liquid metal (LM) plasma-facing components (PFCs) have the potential to alleviate some of the difficult constraints of solid PFCs. The solid substrate that supports these liquids would see only neutron irradiation and is protected from the plasma. Lithium or lithium eutectics would have a high affinity for tritium and deuterium at low operating temperatures and would provide a low recycling environment for the core plasma that seems to provide significant confinement improvements in existing plasma experiments. Liquid metals have sufficient thermal conductivity for good thermal conduction and can provide vapor shielding under transient heat loads. On the other hand, electrically conducting liquids will have magnetohydrodynamic (MHD) interactions that can disturb the surface allowing material to enter the plasma and can laminarize the flow, thereby reducing turbulence and convective heat transport. Sputtering and evaporation must be controlled by limiting the operating temperature. The substrate material must remain covered to survive, and the design for how the LM enters and exits the plasma chamber or divertor region needs to be identified. The present contribution introduces a liquid lithium free-surface cooling system into a future fusion device design developed for the Fusion Nuclear Science Facility (FNSF) program. The design includes LM PFCs covering convex divertor surfaces as well as lithium supply and removal lines. Three-dimensional analysis of the proposed design was performed using a highly customized version of the ANSYS CFX code applying methods of computational fluid dynamics. MHD was introduced using a magneto vector potential approach, allowing a natural interface. Free-surface flow was included using a volume of fluid approach with surface tension on the fluid vacuum interface. Electromagnetic equations were solved for LM as well as for solid components and vacuum. Special stabilization procedures were derived and applied to improve the convergence of the momentum equations with the source terms due to Lorentz force and surface tension. Conjugate heat transfer analysis was performed in LM and solid components. The numerical model was validated using analytical MHD solutions for high Hartmann number flow as well as relevant experimental results. Numerical solutions were obtained for the design configuration including FNSF geometry and Fusion Energy System Studies device parameters obtained from the system studies. Results of the analysis allow determination of the parameter range for the operation of the proposed design as well as design optimization.

Potential Impacts of Liquid-Metal Plasma-Facing Components on Heating and Current Drive Actuators for a Fusion Nuclear Science Facility

This paper addresses the potential impact of liquid metal (LM) plasma-facing components (PFCs) for the heating and current drive (H&CD) actuators on the Fusion Nuclear Science Facility (FNSF) fusion reactor. Fulfilling the high neutron fluence mission of the FSNF requires steady-state operation for extremely long pulses (months to years) between maintenance opportunities. The use of LM as a surface material is one strategy for extending the lifetime of the PFCs for long pulse operation in a high heat flux, high neutron flux environment like that of the FNSF. Liquid metal PFCs provide possible pathways forward on many difficult aspects of a fusion reactor; however, the LM PFCs also bring new challenges and unknowns with respect to the H&CD actuators needed to provide steady-state operation. The development of LM-compatible materials for radio-frequency (RF) antennas will be critical, as well as strategies for minimizing contamination of antenna surfaces and the core plasma. Successful deployment of LM PFCs on the FNSF will require operational experience with RF in a LM environment both on test stands and in an integrated toroidal environment.

Critical Exploration of Liquid Metal Plasma-Facing Components in a Fusion Nuclear Science Facility

Liquid metal (LM) plasma-facing components (PFCs) may provide a resolution to the challenging fusion environment, particularly the first wall and divertor surfaces. Transforming these concepts into viable technologies will require considerable research and development. With the fusion nuclear regime in mind, the Fusion Energy System Studies group examined LM PFCs in order to identify needed research thrusts that could accelerate their development and assess their viability. Liquid metal behavior, solid substrate aspects, and fusion facility integration aspects are examined, with concepts as the research focusing element. The concepts applied to a fusion nuclear device are the primary definer of the LM parameters, environmental conditions, and operational aspects. This forms the research strategy recommended for these complex systems.

Initial Neutronics Investigation of a Liquid-Metal Plasma-Facing Fusion Nuclear Science Facility

The use of a liquid-metal (LM) plasma-facing component (LM-PFC) in fusion reactor designs has some advantages as well as some disadvantages as compared to traditional designs that use a solid plasma-facing wall. Neutronics analysis of these potential LM-PFC concepts is important in order to ensure that radiation limits are met and that system performance meets expectations.A three-dimensional (3-D) neutronics analysis parametric study considering four LM first-wall (FW) candidates, (PbLi, Li, Sn, and SnLi) was performed with a thin (2.51-cm) LM-PFC design. The 3-D neutronics study used a fusion reactor based on the Fusion Energy Systems Study (FESS) Fusion Nuclear Science Facility (FNSF) (FESS-FNSF) that served as the baseline for comparison. FESS-FNSF is a deuterium-tritium–fueled tokamak with 518 MW of fusion power. A partially homogenized 3-D computer-aided-design model of the LM-PFC FNSF design was analyzed using the DAG-MCNP5 transport code.The results show that all candidate LM designs are acceptable with 4% to 13% increases in the tritium breeding ratio compared to the baseline case. The peak displacements per atom at the FW decrease 2% to 15%. For all four LM designs examined, the magnet heating and fast neutron fluence are well below acceptable limits. Overall, the Li LM design is the best candidate from a neutronics perspective.

Study of liquid metal surface wave damping in the presence of magnetic fields and electrical currents

Abstract Experiments and predictions of surface wave damping in liquid metal due to a surface aligned magnetic field and externally regulated j × B force are presented. Fast-flowing, liquid-metal plasma facing components (LM-PFCs) are a proposed alternative to solid PFCs that are unable to handle the high heat flux, thermal stresses, and radiation damage in a tokamak. The significant technical challenges associated with LM-PFCs compared to solid PFCs are justified by greater heat flux management, self-healing properties, and reduced particle recycling. However, undesirable engineering challenges such as evaporation and splashing of the liquid metal introduce excessive impurities into the plasma and degrade plasma performance. Evaporation may be avoided through high-speed flow that limits temperature rise of the liquid metal by reducing heat flux exposure time, but as flow speed increases the surface may become more turbulent and prone to splashing and uneven surfaces. Wave damping is one mechanism that reduces surface disturbance and thus the chances of liquid metal impurity introduction into the plasma. Experiments on the Liquid Metal eXperiment Upgrade (LMX-U) examined damping under the influence of transverse magnetic fields and vertically directed Lorentz force.

A Review of Recent Studies on Particle Recycling From Liquid Metals With/Without Convection Under Plasma Bombardment

From the recent experiments on liquid metal plasma-facing components, convection appears to play an important role in maintaining reduced recycling conditions. Either it is natural or forced convection, the transport of the implanted particle is accelerated in the depth direction whereby the surface saturation would be delayed or avoided. Reviewed in this paper are some of the recent studies on particle recycling from liquid metals under plasma bombardment with the emphasis on liquid convection effects. Natural convection has been observed to enhance deuterium plasma-driven permeation. In addition, the effects of J × B forced convection on particle recycling have been extensively studied under steady-state hydrogen, deuterium, helium, and argon plasma bombardment. Also, preliminary fluid dynamics analysis has been conducted to interpret these experimental observations.