Capillary Porous System Research Articles

Optimization of lithium vapor box divertor evaporator location on NSTX-U using SOLPS-ITER

Commercial fusion reactors will be faced with extremely high divertor target heat fluxes that will require mitigation. Simulations of detachment in an NSTX-U scenario projected to have 92 MW m−2 unmitigated peak target heat flux are presented, which reaches sub-10 MW m−2 target heat flux using a highly dissipating lithium vapor box divertor design. The lithium vapor box is a detached divertor design which employs lithium vapor evaporation and condensation to contain lithium below the X-point. Previous SOLPS modeling has indicated a lithium vapor box can reduce the heat flux down to 10 MW m−2 via simultaneous evaporation from the Private Flux Region (PFR) and the Common Flux Region (CFR) sides of the vapor box. It is found here that PFR evaporation has improved access to the separatrix leading to significantly more efficient power dissipation than CFR evaporation. Simulations of target evaporation with an evaporation distribution that is self-consistent with the temperature of a Capillary Porous System with Fast flowing liquid lithium could reach nLi / ne∼ 0.025–0.030 at the Last Closed Flux Surface (LCFS) depending on the liquid metal flow speeds and lithium sputtering yield, while PFR-side evaporation can reach acceptable heat fluxes with nLi / ne∼ 0.038 at the LCFS. However, PFR evaporator performance can be improved if the target is allowed to be hot enough such that it reflects lithium, reaching nLi / ne∼ 0.028 and reducing required lithium evaporation. Ultimately PFR evaporation and target evaporation are found to have similar ability to produce acceptable heat flux solutions with minimal upstream concentration.

Stabilization of liquid tin surfaces under D plasma irradiation by a capillary porous system

Liquid metal divertors are discussed as a potential alternative to divertor components made entirely of solid materials such as tungsten. However, liquid metal interaction with H isotope plasmas poses entirely new challenges, including the stability of the liquid surface. In this article, the interaction of low-temperature D plasmas with both free liquid tin surfaces, and the liquid metal confined in a capillary porous system (CPS) is presented. Free surfaces showed intolerable instabilities due to formation of gas bubbles in the melt, as opposed to a strong stabilizing effect of the CPS. A tendency of liquid tin to well up and entirely cover the surface of the CPS may be beneficial in terms of quickly re-establishing a tin surface after depletion by transient overloading. On the other hand, this appears to counteract efforts to fully suppress superficial bubble formation and bursting, and the resulting ejection of tin droplets by designing a CPS with very small pores.

Conceptual design of a 3D printed liquid lithium divertor test modular for EAST

The utilization of Liquid Metal Divertor (LMD) stands as a promising prospect for the divertor component in DEMO. To explore the vapor shielding effect and provide technical accumulation for the development of DEMO LMD, the imperative development of a high-performance LMD test module has arisen. The Experimental Advanced Superconducting Tokamak (EAST) has amassed substantial expertise in LM first wall design and experimentation, rendering it suitably equipped for experimental pursuits. Therefore, this paper aims to design a test module running in the mid-plane of EAST to accumulate technical experience for the application of 3D printed capillary porous system (CPS) in LMD. Drawing upon prior experience, specific design requirements are articulated. Lithium is chosen as the operational LM due to its favorable balance between heat dissipation capacity and compatibility with the core plasma. The conceptual design encompasses active water cooling components, a CPS, and a lithium channel. Thermal analysis is conducted to ascertain the prevention of excessive evaporation or frozen during operation. The maximum power handling capacity of this design is projected, with practical solutions outlined for inter-component thermal management. The results affirm the viability of this design within the thermal load parameters of the EAST experiment, offering invaluable insights for designers exploring diverse LMD configurations.

Challenges towards an acceleration in stellarator reactors engineering: The dual coolant lithium–lead breeding blanket helical-axis advanced stellarator case

Under the ambitious EUROfusion mission of “bringing the stellarator line to technological maturity”, the development of a Dual Coolant Lithium–Lead (DCLL) Breeding Blanket (BB) for a Helical-Axis Advanced Stellarator (HELIAS) started. The BB is the crucial systems to achieve tritium self-sufficiency in fusion power plants. The DCLL has potentialities to answer the challenges posed by complex HELIAS configuration, having liquid breeder and decoupled first wall (FW) and breeding zone circuits. Both characteristics are being empowered to simplify remote maintenance and integration of the BB segments. Hence, a “quasi-toroidal” BB segmentation has been proposed to minimize the magnetohydrodynamic pressure drop eschewing complex electrical insulating components while hindering maintenance. Such controversy motivated the use of a detached FW small panels manageable through ports. On this basis, a decoupled Capillary Porous System FW has been assessed under thermal-hydraulics and neutronics point of view. Moreover, ad-hoc tools have been developed for the parametrization of models and convergence toward a viable DCLL HELIAS design, speeding-up the coupling of computer-aided design modelling and analyses. Such novel strategies are described in view of a potential acceleration of the stellarator reactor engineering and by providing an overview of the stellarator challenges inside a global context.

MHD Flow in Simple Cubic Periodic Array Geometry

The aim of this study is to investigate the behaviour of liquid metal flow in Capillary Porous System (CPS) under strong external magnetic field. Overlapping simple cubic (SC) periodic array of electrically non-conducting spheres with diameter 6 mm and distance between spheres centres 5.6 mm is 3D printed from PLA electrically non-conducting filament. At room temperature, flow of up to 50 mL/s of In–Ga–Sn in pore space in magnetic field of superconducting magnet up to 5T is investigated. Three orientations of magnetic field in relation to the main flow in SC cell are considered—colinear with main flow and perpendicular to it. The values of Reynolds, Hartmann and Stuart numbers in experiment are up to 1160, 90 and 350, respectively. The results indicate that parallel to the main flow orientation of magnetic field has little influence on the flowrate, while perpendicular orientation strongly reduces flowrate with dependence close to 1/Ha, which agrees well with ANSYS Fluent simulations in a unit SC cell, resembling results for channel flow in magnetic field.

Depth profile CF LIBS analysis of the wall deposited layer in the COMPASS tokamak after LiSn testing campaign

Plasma-facing materials in tokamak nuclear reactors are subject to intense heat and radiation. The design of liquid metal (LM) divertor walls has several advantages over the solid counterparts. It is important to understand the migration and re-deposition of LMs such as lithium (Li), lead (Pb) or even tin (Sn). This work presents CF LIBS depth profile analysis of the deposited layer on Ni–Cr based screws situated at different places in the COMPASS tokamak vessel during the Capillary Porous System (CPS) LM (LiSn) divertor testing campaign. The experiment was carried out at low Ar pressure (100 mbar) using ns Nd:YAG laser operating at 532 nm. The spectra were recorded using echelle spectrometer (M5000, Andor Tech.) equipped with an iCCD camera (iStar DH743, Andor Tech.). The quantification was based on observed C I, B I, Li I and (weak) Sn I lines, in addition to trace elements (Ca, Na, K) and main matrix elements (Cr, Ni, Fe). The evaluation of electron temperature and density was based on Cr I-II, Ni-II and Fe I-II lines. The LM based content is estimated to be Li (0.3-0.81 at.%) and Sn (0.1-0.23 at.%) with Li/Sn at.% ratio ranging from 3 to 3.5 (wt.% ratio of 0.17-0.20). In practise, the limit of detection of Sn by CF LIBS for this type of Cr-Ni-Fe based matrix is observed to be ∼0.1 at.%.

High-temperature test of tin-lithium CPS under deuterium plasma irradiation conditions

This paper is devoted to experiments on testing of the Sn-Li capillary porous system (CPS) under conditions of deuterium plasma irradiation, carried out at a plasma-beam installation (PBI). As a metal CPS matrix, molybdenum mesh was used. The paper presents a detailed description of the development of technology and procedure for the fabrication of the investigated sample, intended for plasma testing, as well as experiments on irradiation of Sn-Li CPS with deuterium plasma. As a result of the experiments performed, the dependences of the temperature of the investigated sample on the energy of the plasma contacting with the CPS, time dependence of the gas phase composition in the PBI chamber during irradiation of Sn-Li CPS with deuterium plasma, optical spectra depending on the temperature were obtained. Post-experimental material science studies with a sample of Sn-Li CPS were also performed and the results of microstructure, thermal and X-ray phase analysis were obtained. Analysis of the experimental data obtained showed that the energy of deuterium plasma precipitated on the Sn-Li alloy is re-emitted into the energy of optical radiation on the evaporating neutral atoms of lithium and tin. A complete evaporation of the alloy from CPS, during interacting with deuterium plasma, leads to partial destruction of the metal matrix of molybdenum.

Physics and Technology Research for Liquid-Metal Divertor Development, Focused on a Tin-Capillary Porous System Solution, at the OLMAT High Heat-Flux Facility

The operation of the Optimization of Liquid Metal Advanced Targets (OLMAT) facility began in April 2021 with the scientific objective of exposing liquid-metal plasma facing components (PFCs) to the particle and power fluxes provided by one of the hydrogen neutral beam injectors of the TJ-II stellarator. The system can deliver heat fluxes from 5 to 58 MW m−2 of high energy hydrogen neutral particles (≤ 33 keV) with fluxes up to 1022 m2 s−1 (containing an ion fraction ≤ 33% in some instances), pulsed operation of 30–150 ms duration and repetition rates up to 2 min−1. These characteristics enable OLMAT as a high heat flux (HHF) facility for PFC evaluation in terms of power exhaust capabilities, thermal fatigue and resilience to material damage. Additionally, the facility is equipped with a wide range of diagnostics that includes tools for analyzing the thermal response of the targets as well as for monitoring atomic/plasma physics phenomena. These include spectroscopy, pyrometry, electrical probing and visualization (fast and IR cameras) units. Such particularities make OLMAT a unique installation that can combine pure technological PFC research with the investigation of physical phenomena such as vapor shielding, thermal sputtering, the formation/characterization of plasma plumes with significant content of evaporated metal and the detection of impurities in front of the studied targets. Additionally, a myriad of surface characterization techniques as SEM/EDX for material characterization of the exposed PFC prototypes are available at CIEMAT. In this article, first we provide an overview of the current facility upgrade in which a high-power CW laser, that can be operated in continuous and pulsed modes (0.2–10 ms), dump and electrical (single Langmuir) probe embedded on the target surface have been installed. This laser operation will allow simulating more relevant heat loading scenarios such as nominal steady-state divertor heat fluxes (10–20 MW m−2 in continuous mode) and transients including ELM loading and disruption-like events (ms time scales and power densities up to GW m−2 range). The work later focuses on the more recent experimentation (2022 fall campaign) where a 3D printed Tungsten (W) Capillary Porous System (CPS) target, with approximated 30 μm pore size and a 37% porosity and filled with liquid tin. This porous surface was a mock-up of the PFC investigated in the ASDEX Upgrade divertor manipulator. The target composed with this element was eventually exposed to a sequence of shots with the maximum heat flux that OLMAT provides (58 ± 14 MWm−2). Key questions as resilience to dry-out and particle ejection of the liquid metal layer, its refilling, the induced damage/modification of the porous W matrix and the global performance of the component are addressed, attempting to shed light on the issues encountered with the PFC at tokamak scale testing.

Predictive and interpretative modelling of ASDEX-upgrade liquid metal divertor experiment

A liquid metal Capillary Porous System (CPS) test module filled with tin was studied in the ASDEX Upgrade (AUG) outer divertor. The CPS module was flush mounted as part of a target tile and exposed using the AUG divertor manipulator. In order to predict tin erosion from the designed module under typical AUG divertor loading conditions, the experiment was interpreted using the HeatLMD code. Preceding test exposures of the CPS in the high heat flux facility GLADIS were performed and interpreted by modelling to quantify the thermo-mechanical properties of the module. The results for the reference AUG discharge indicated a total of 2.6 × 1017 tin atoms (51 μg) would be eroded during the exposure, predominantly through temperature enhanced sputtering. The vapour cooling power was predicted to be negligible (5 kW/m2at the end of a 5 s exposure with heat flux from the plasma of 2 MW/m2). The module was expected to be compatible with plasma operation, with tin erosion too low for any significant effect on the plasma performance. However, interpretative modelling of the experimental discharge with the highest exposure time yielded significantly lower tin erosion than observed. To be attributed to tin radiation the experimentally observed increase in total radiative power (1.5 MW) would require 2 × 1018 tin atoms (peak calculated erosion rate) radiating in the core plasma. This would require every tin atom eroded, to reach the core, which is unlikely.

Neutronic Assessments towards a Novel First Wall Design for a Stellarator Fusion Reactor with Dual Coolant Lithium Lead Breeding Blanket

The Stellarator Power Plant Studies Prospective R&D Work Package in the Eurofusion Programme was settled to bring the stellarator engineering to maturity, so that stellarators and particularly the HELIAS (HELical-axis Advanced Stellarator) configuration could be a possible alternative to tokamaks. However, its complex geometry makes designing a Breeding Blanket (BB) that fully satisfies the requirements for such a HELIAS configuration, which is a difficult task. Taking advantage of the acquired experience in BB design for DEMO tokamak, CIEMAT is leading the development of a Dual Coolant Lithium Lead (DCLL) BB for a HELIAS configuration. To answer the specific HELIAS challenges, new and advanced solutions have been proposed, such as the use of fully detached First Wall (FW) based on liquid metal Capillary Porous Systems (CPS). The proposed solutions have been studied in a simplified 1D model that can help to estimate the relative variations in Tritium Breeding Ratio (TBR) and displacement per atom (dpa) to verify their effectiveness in simplifying the BB integration and improving the machine availability while keeping the main BB nuclear functions (i.e., tritium breeding, heat extraction and shielding). This preliminary study demonstrates that the use of FW CPS would drastically reduce the radiation damage received by the blanket by 29% in some of the selected configurations along with a small decrease of 4.9% in TBR. This could even be improved to just a 3.8% TBR reduction by using a graphite reflector. Such an impact on the TBR is considered affordable, and the results presented, although preliminary in essence, have shown the existence of margins for further development of the FW CPS concept for HELIAS, as they have been not found, at least to date, to be significant showstoppers for the use of this technological solution.

Liquid Sn corrosion behaviors to high-flux hydrogen plasmas irradiated Mo capillary-pore systems

This paper studied the effects of hydrogen plasma irradiation on the corrosion resistance of Mo capillary porous systems (CPSs) in high temperature liquid Sn. Initial Mo CPSs showed a significant morphology change and mass loss rate (1.107 × 10–3 mg/(mm2·h)) after corrosion in liquid Sn at 1,023 K for 100 h. A brief period of irradiation enhanced the corrosion resistance of Mo wires, resulting in a dramatic decrease to 1.23 × 10–4 mg/(mm2·h) in mass loss rate under the same corrosion conditions. To determine whether temperature was the main factor leading to above phenomenon, Mo CPSs were pre-annealed at the same temperature (843 K) as irradiation. The mass loss rate of annealed Mo CPSs (3.09 × 10–4 mg/(mm2·h)), which was lower than that of the initial sample, was still higher than that of the plasma-treated samples. Difference between plasma irradiation and heat treatment was the incident of various particles in hydrogen plasma. Therefore, the suppressed corrosion phenomenon caused by plasma could not only be attributed to the function of high temperature but its synergistic effect with hydrogen isotope retention.

Comparative study of different Sn wetted W CPSs exposed to NBI fluxes in the OLMAT facility

Four different tin-wetted, tungsten CPS (Capillary Porous System) targets where exposed to NBI pulses in the OLMAT High Heat flux (HHF) facility. They include two flexible ones placed on a TZM support (W meshes and W felt) and two compact ones (sintered W disk and 3D printed W). A comparative study was performed using a fast-frame imaging camera and an infrared pyrometer. Surface temperature increase and homogeneity, particle ejection, CPS damage and overall behaviour were studied for each case. Sn drop/accumulation at the lower part of the targets was observed for all cases when they are heated up to around 400 °C except for the 3D printed W target that has its own Sn deposit. The 3D printed W target presented the best results in all aspects, withstanding heat pulses up to 58 MW/m2 in 100 ms without any damage or particle ejection. On the other hand, the W mesh targets displayed damage at 20 MW/m2 due to a bad thermal contact with the deposit, while the sintered W disk developed a crack during a series of 15 MW/m2 NBI pulses. As might be expected, a reduced increase of temperature during pulses is observed for the two compact W targets. The results and their relevance for the design of a Sn wetted W CPS for application as a DEMO-divertor material are discussed in the present work.

First study of lithium boron composite as plasma facing material

Lithium-Boron Composite Material (LBCM) is presented as a plasma-facing material with a lot of promise from the perspective of liquid metal first wall. LBCM consists of ∼ 20 w.% boron and ∼ 80 w.% lithium, arranged in the form of a Li5B4 matrix filled with metal lithium, similar to capillary porous systems (CPS) already used as plasma-facing elements. The characteristic matrix cell size is approximately 5 µm. LBCM was subjected to electron flux and helium plasma in a linear PR-2 device. LBCM maintained physical integrity up to T > 900 °C. Boron didn’t evaporate from LBCM under electron irradiation, but was sputtered during helium bombardment. CPS-like properties, wherein Li from the whole of the LBCM sample was transported to the area of the highest thermal load were observed.

Strategies to enhance the moisture-barrier qualities of concrete mixtures to improve their durability

Moisture transport in concrete significantly impacts its durability attribute, which in turn affects the useful service life of the built concrete infrastructure. A host of physical, chemical, and mechanical deterioration processes of concrete depend on the presence of moisture inside the concrete. Enhancement of the moisture-barrier characteristic of concrete can thus be the key to improving its durability. This paper reports the test results of various strategies implemented to reduce the moisture transport into concrete. These strategies include (i) use of fly ash and silica fume as partial replacement of cement for refinement of capillary porosity, discontinuity of pores, and refinement of the chemistry of hydrated cement matrix; (ii) use of milled waste glass as partial replacement of cement to refine the microstructure of cementitious mixture (iii) use of hydrophobic additives to reduce the affinity of capillary pore surfaces to moisture; and (iv) use of polymer emulsion to line capillary pore surfaces to cause partial blockage of the capillary pore system. Five different concrete mixtures including a control mixture were prepared using the above formulations and tested for moisture sorption, acid attack resistance, abrasion resistance, and compressive strength characteristics at 28 and 90 days of concrete age. Test results indicated enhancement in compressive strength, moisture resistance, and other durability characteristics of the modified mix formulations compared to that of control mixture. Mix formulation incorporating fly ash and silica fume as partial replacement of cement proved to be the most effective combination for achieving the desired improvements in mechanical and durability attributes of concrete. The findings of this study are expected to provide guidelines for designing concrete mixtures with enhanced durability when exposed to aggressive environmental conditions.[copyright information to be updated in production process.]

Study of Plasma Interaction with Liquid Lithium Multichannel Capillary Porous Systems in SCU-PSI

In this paper, an embedded multichannel capillary porous system (EM-CPS) was designed and fabricated with 304 stainless steel using the laser ablation method. The EM-CPS revealed its excellent ability to wick liquid lithium to its surface effectively. The interaction between Li-prefilled EM-CPS and plasma was studied, and the results showed that the surface temperature decreased by ~140 °C compared with the results of the experiment of EM-CPS without lithium filling. Additionally, EM-CPS displayed a better heat transfer performance and stronger radiation loss of the vapor cloud than the traditional woven tungsten-based meshes. In addition, the drift of the lithium vapor cloud center was found during plasma irradiation and led to a decrease in the intensity of the Li 670.78 nm emission line detected by the spectrometer at the observation point. When the thermal load deposited on the sample surface is reinforced by increasing the magnetic field, the rise in surface temperature is restrained due to the enhanced heat dissipation capability of lithium. SEM images of irradiated samples showed that the 304 stainless steel-based EM-CPS has corrosion problems due to the interaction between liquid lithium and argon plasma, but it still showed good plasma-facing characteristics. These findings provide a reference for further studies of embedded multichannel CPSs with plasma-facing components (PFCs) in linear plasma devices and tokamaks in the future.

Interaction of an unwetted liquid Li-based capillary porous system with high-density plasma

This study examined the effects of plasma irradiation on an unwetted liquid lithium-based capillary porous system (Li-CPS). The Li-CPS was irradiated with high-density Ar plasma using a linear plasma device at Sichuan University for Plasma Surface Interaction. The high-speed camera, Langmuir probe, and multi-channel spectrometer were used to characterize the effects of plasma irradiation. Upon Ar plasma irradiation, liquid Li drops were formed on the surface of the unwetted Li-CPS. Immediately after this irradiation, the drops fractured and were ejected into the plasma within ∼20 ms scale, which is not observed before to the best of our knowledge. Related results showed that the ejection behavior of Li could effectively cool electron temperature and reduce incident heat flux by ∼30% and correspondingly matrix temperature ∼150 °C, revealing an enhanced vapor shielding effect. The involved internal mechanism and physical processes deserve further investigations.

Plasma facing components with capillary porous system and liquid metal coolant flow

Liquid metal can create a renewable protective surface on plasma facing components (PFC), with an additional advantage of deuterium pumping and the prospect of tritium extraction if liquid lithium (LL) is used and maintained below 450 °C, the temperature above which LL vapor pressure begins to contaminate the plasma. LM can also be utilized as an efficient coolant, driven by the Lorentz force created with the help of the magnetic field in fusion devices. Capillary porous systems can serve as a conduit of LM and simultaneously provide stabilization of the LM flow, protecting against spills into the plasma. Recently, a combination of a fast-flowing LM cooling system with a porous plasma facing wall (CPSF) was investigated [A. Khodak and R. Maingi, Nucl. Mater. Energy 26, 100935 (2021)]. The system takes an advantage of a magnetohydrodynamics velocity profile as well as attractive LM properties to promote efficient heat transfer from the plasma to the LL at low pumping energy cost, relative to the incident heat flux on the PFC. In the case of a disruption leading to excessive heat flux from the plasma to the LM PFCs, LL evaporation can stabilize the PFC surface temperature, due to high evaporation heat and apparent vapor shielding. The proposed CPSF was optimized analytically for the conditions of a fusion nuclear science facility [Kessel et al., Fusion Sci. Technol. 75, 886 (2019)]: 10 T toroidal field and 10 MW/m2 peak incident heat flux. Computational fluid dynamics analysis confirmed that a CPSF system with 2.5 mm square channels can pump enough LL so that no additional coolant is needed.

Improving the frost resistance of roof tiles beyond current prediction schemes

Frost resistance is an important requirement for clay roof tiles and the most difficult to keep under control during industrial production. Durability under freeze/thaw cycles is related with the capillary pore system, and current models predict the lower the open porosity and the coarser the pore size, the better the frost resistance. This implies, however, high firing temperature and rather refractory clay bodies, which are in contrast with energy and resource efficiency. Therefore, a different approach is needed to improve frost resistance of roof tiles without stressing the concept of low porosity and coarse pore size. A case-study is presented to demonstrate how excellent frost resistance can be achieved by adjusting raw materials formulation and firing schedule. Raw materials and bodies were characterized by XRF, ASTM C958 and technological properties. Both laboratory tests were performed: the products were characterized by water absorption (ASTM C67), open porosity and pore size distribution (Hg porosimetry), phase composition (XRD-Rietveld), mechanical strength (EN 538) and frost resistance (EN 539-2) up to 400 freeze/thaw cycles. Durability of roof tiles was drastically improved acting on both pore size distribution (eliminating pores <0.1 μm) and increasing mechanical strength (>13 MPa). Phase composition plays a complex role with opposite effects of new formed phases versus amorphous phase and residual clay minerals. A satisfactory target (no damages after 250 freeze/thaw cycles) was achieved firing at 900 °C (7% pores <0.1 μm) while the best performance (no damages after 400 cycles) required firing at 950 °C (<1% pores <0.1 μm). Excellent frost resistance (well beyond the standard 50 cycles) can be obtained through proper design of firing schedule and body composition, even for temperatures below 950 °C.

Overview of the TJ-II stellarator research programme towards model validation in fusion plasmas

TJ-II stellarator results on modelling and validation of plasma flow asymmetries due to on-surface potential variations, plasma fuelling physics, Alfvén eigenmodes (AEs) control and stability, the interplay between turbulence and neoclassical (NC) mechanisms and liquid metals are reported. Regarding the validation of the neoclassically predicted potential asymmetries, its impact on the radial electric field along the flux surface has been successfully validated against Doppler reflectometry measurements. Research on the physics and modelling of plasma core fuelling with pellets and tracer encapsulated solid pellet injection has shown that, although post-injection particle radial redistributions can be understood qualitatively from NC mechanisms, turbulence and fluctuations are strongly affected during the ablation process. Advanced analysis tools based on transfer entropy have shown that radial electric fields do not only affect the radial turbulence correlation length but are also capable of reducing the propagation of turbulence from the edge into the scrape-off layer. Direct experimental observation of long range correlated structures show that zonal flow structures are ubiquitous in the whole plasma cross-section in the TJ-II stellarator. Alfvénic activity control strategies using ECRH and ECCD as well as the relation between zonal structures and AEs are reported. Finally, the behaviour of liquid metals exposed to hot and cold plasmas in a capillary porous system container was investigated.

Vapour shielding of liquid-metal CPS-based targets under ELM-like and disruption transient loading

This paper presents experimental studies of plasma-surface interactions during powerful plasma impacts of a quasi-stationary plasma accelerator (QSPA) on the Sn capillary porous systems (CPSs) in conditions simulating disruption and edge localized modes (ELM) like loads. Experiments were carried out using two QSPA devices. ELM-like plasma exposures were performed with QSPA-M test-bed facility. A large-scale QSPA Kh-50 device was used to simulate plasma disruptions and giant ELMs. Variation of the plasma stream energy density has been performed to study the onset of vapour shield. It is shown that during plasma exposures of a Sn-CPS target with the QSPA plasma load <1 MJ m−2, single dust particles traces have been registered. A further increase in the heat load leads to the splashing of the eroded material. For ELM-like impacts, a rather weak melt motion was observed on the target surface. A post-mortem analysis has shown that the CPS structure was not destroyed in the course of many repetitive ELM-like pulses. Surface morphology has changed from a smooth surface to corrugation structures with the formation of some cavities in mesh cells due to the influence of the surface tension and capillary effects. Spectral lines of Sn I and Sn II have been identified by optical emission spectroscopy in the near-surface plasma. A plasma shield, that consists mostly of Sn neutrals appears at Q ∼ 0.1 MJ m−2. An increase in the surface heat load resulted in the intensive emission of Sn II lines, which started to be observed at Q ∼ 0.3 MJ m−2. The plasma electron density near the surface increases significantly at Q > 0.5 MJ m−2, which corresponds to the strong vapour shielding of the exposed surface. A comparison between the obtained results on the vapour shielding of Sn CPS and available numerical simulation using the TOKES code has been performed.