Capillary Porous System Research Articles

Justification of the Production Process of Pressed Wood and Study of its Properties

Results of a numerical analysis of the stress-strain state of wood during its pressing in different symmetry directions of the anisotropic material are presented. It is shown that the anisotropy of mechanical properties of wood is an important factor determining both the structural characteristics of the porous system and its strength. A mathematical modeling of the process of pressing wood as a three-phase anisotropic rheologically complex capillary-porous system allows one to predict parameters of the resulting wood composite. The compressed wood obtained by the production modes developed has a tensile strength eight times greater than that of the natural one, which is comparable to the strength of the St3 steel, but its specific strength is higher than that of the St45 steel. Compression and impregnation of softwood species with an aqueous solution of carbamide allows one to harden them. This kind of treatment endows the wood with enhanced strength characteristics comparable to the characteristics of the St3 steel. The special features of tensile tests used to estimate the elastic modulus and strength characteristics of such materials are considered. Data obtained by different testing methods are correlated, and characteristics of the strengthened wood and some brends of steel are compared.

Исследование поведения капиллярно-пористых систем с жидким литием при воздействии импульсной дейтериевой плазмы

Исследование поведения капиллярно-пористых систем с жидким литием при воздействии импульсной дейтериевой плазмы

Comparative studies of liquid metals for an alternative divertor target in a fusion reactor

Two liquid metals (LM), Li and LiSn (20:80 at), presently considered as alternative materials for the divertor target of a fusion reactor, have been exposed to the plasma in a capillary porous system (CPS) arrangement in TJ-II. A negligible perturbation of the plasma has been recorded in both cases, even when stellarator plasmas are particularly sensitive to high Z elements due to the tendency to central impurity accumulation. The surface temperature of the LM CPS samples (made of a tungsten mesh impregnated in SnLi or Li) has been measured during the plasma pulse with ms resolution by pyrometry and the thermal balance during heating and cooling has been used to obtain the thermal parameters of the SnLi and Li CPS arrangements. Temperatures as high as 1150 K during TJ-II plasma exposure were observed for the LiSn solid case. Strong changes in the thermal conductivity of the alloy were recorded in the cooling phase at temperatures close to the nominal melting point. The deduced values for the thermal conductivity of the LiSn alloy/CPS sample were significantly lower than those predicted from their individual components.

Tin re-deposition and erosion measured by cavity-ring-down-spectroscopy under a high flux plasma beam

Cavity-ring-down spectroscopy (CRDS) was implemented to measure the re-deposition of liquid tin under a high flux plasma beam in the linear plasma device Pilot-PSI. A capillary porous system (CPS) consisting of a molybdenum cup and tungsten meshes (pores diameters of 0.2 mm and 0.44 mm) was filled with tin and exposed to argon plasma. The absorption of a UV laser-beam at 286.331 nm was used to determine a number of sputtered neutral tin atoms. The incoming flux of argon ions of ~50 eV was 1.6–2.7 × 1023 m−2 s−1, and the sample temperature measured by pyrometry varied from 850 °C to 1200 °C during exposures. The use of CRDS for measuring absolute number of particles under such plasma exposure was demonstrated for the first time. The number of sputtered tin particles in the cavity region assuming no losses would be expected to be 5.5 × 1011–1.2 × 1012 while CRDS measurements showed only 5.7–9.9 × 108. About 98–99.8% of sputtered particles were therefore found to not reach the CRDS observation volume. Spectroscopic ratios of Sn I to Sn II ions, as well as equilibrium considerations, indicate that fast ionization as well as plasma entrainment of neutrals is responsible for the discrepancy. This would lead to high re-deposition rates, implying a lowered contamination rate of core plasma and lower required replenishment rates at high-flux conditions than would otherwise be expected.

Model identification of the temperature over the FTU cooled liquid lithium (CLL) limiter surface

In this work, a data-driven model procedure aimed at identifying the dynamical behavior of the thermal distribution over the limiter surface placed in nuclear fusion plant facilities is provided. In particular, we focused on experimental data collected in the in Frascati Tokamak Upgrade (FTU) where a cooled liquid lithium limiter (CLL) with a capillary porous system (CPS) technology is adopted. Thus, a nonlinear dynamical system, namely a Hammerstein–Wiener model, has been investigated and opportunely identified in order to predict the thermal distribution over the CLL. The identified system is able to predict spatiotemporal thermal information even in the worst case scenario when disruptive events occur during plasma experiments.

Enhanced erosion of lithium surface with capillary porous system

Formation of lithium vapor cloud occurs above lithium surface as temperature goes up. Experiments devoted to investigating lithium vapor cloud interacting with expanding argon plasma under applied electric field have been carried out in a linear plasma device. Lithium spectrum has been characterized by utilizing optical emission spectroscopy (OES) and many emission lines of lithium atoms have been observed, including Li_670.78nm (1.9eV), Li_610.36nm (3.87eV), Li_460.30nm (4.54eV) and Li_323.26nm (3.83eV). Enhanced erosion of lithium surface caused by surface adatoms was found when bias is high, its effective adatoms sublimation energy was calculated to be 1.72eV at the high temperature through Arrhenius plot in enhanced region. The surface temperature of liquid lithium has been monitored by a thermocouple. Since incident argon ion energy has been elevated due to the applied electric field acceleration, the temperature of lithium surface will have different behaviors with different biases, and it turns out that the temperature has a linear relation with bias, about an increase of 16–17°C per 5V bias voltage. By calculating evaporation power, excitation power and ionization power, indicating that at temperatures above 700–800°C, heat flux dissipated in the lithium vapor can have a huge meaningful decrease.

Complex of lithium and tungsten limiters for 3 MW of ECR plasma heating in T-10 tokamak. Design, first results

A complex of tungsten and lithium limiters is developed. It is expected that application of W as a plasma facing material will allow excluding carbon influx into the vacuum chamber. An additional Li limiter, arranged in the shadow of the W one, will be used as a Li source. The parameters and design of limiters are presented. The plasma facing surface of the Li limiter is constructed to make use of a capillary-porous system (CPS). The porous matrix of the CPS provides stability of liquid Li surface under magnetohydrodinamic force effects, and facilitates its constant renewal due to capillary forces. It is shown that the upgrade of limiters in tokamak Т-10 will allow the provision of electron cyclotron resonance (ECR) plasma heating with power up to 3 MW at reasonable Li flux. The first results on Li–W experiments with ECR heating are presented and discussed. Li limiter design and limiter arrangement configuration for a steady state operating tokamak with a closed cycle of lithium circulation are considered.

Investigation of hydrogen isotopes interaction with lithium CPS under reactor irradiation

This work describes the experimental results of a study of tritium generation and release from the lithium capillary porous system (CPS) under neutron irradiation. The experiments were performed at the IVG1.M research reactor (Kurchatov, Kazakhstan) at a power level of 6MW and temperatures from 325 to 840°С. The studies were performed using two modes: with constant pumping out of the experimental ampoule device (differential mode) and with tritium accumulation in ampoule device (AD) with absence of the pumping out (integrated mode). The diffusion coefficients of free tritium atoms in liquid lithium under neutron irradiation were obtained. The Arrhenius dependence of free tritium atoms diffusion coefficient in lithium was derived as D=0.17·exp(−145/RT).

Liquid tin limiter for FTU tokamak

The liquid Sn in a matrix of Capillary Porous System (CPS) has a high potential as plasma facing material in steady state operating fusion reactor owing to its physicochemical properties. However, up to now it has no experimental confirmation in tokamak conditions. First steady state operating limiter based on the CPS with liquid Sn installed on FTU tokamak and its experimental study is in progress. Several aspects of the design, structural materials and operation parameters of limiter based on tungsten CPS with liquid Sn are considered. Results of investigation of corrosion resistance of Mo and W in Sn and their wetting process are presented.The heat removal for limiter steady state operation is provided by evaporation of flowing gaswater spray. The effectiveness of such heat removal system is confirmed in modelling tests with power flux up to 5MW/m2.

Comparative analysis of the possibility of applying low-melting metals with the capillary-porous system in tokamak conditions

The use of capillary-porous systems (CPSs) with liquid Li, Ga, and Sn is considered as an alternative for solving the problem of creating plasma-facing elements (PFEs) of the fusion neutron source (FNS) and the DEMO-type reactor. The main advantages of CPSs with liquid metal compared with hard materials are their stability with respect to the degradation of properties in tokamak conditions and capability of surface self-restoration. The evaluation of applicability of liquid metals is performed on the basis of the analysis of their physical and chemical properties, the interaction with the tokamak plasma, and constructive and process features of in-vessel elements with CPSs implementing the application of these metals in a tokamak. It is shown that the upper limit of the PFE working temperature for all low-melting metals under consideration lies in the range of 550–600°С. The decisive factor for PFEs with Li is the limitation on the admissible atomic flux into plasma, while for those with Ga and Sn it is the corrosion resistance of construction materials. The upper limit of thermal loads in the steady-state operating mode for the considered promising PFE design with the use of Li, Ga, and Sn is close to 18–20 MW/m2. It is seen from the analysis that the use of metals with a low equilibrium vapor pressure of (Ga, Sn) gives no gain in extension of the region of admissible working temperatures of PFEs. However, with respect to the totality of properties, the possibility of implementing the self-restoration and stabilization effect of the liquid surface, the influence on the plasma discharge parameters, and the ability to protect the PFE surface in conditions of plasma perturbations and disruption, lithium is the most attractive liquid metal to create CPS-based PFEs for the tokamak.

Reactor plasma facing component designs based on liquid metal concepts supported in porous systems

The use of liquid metals (LMs) as plasma facing components in fusion devices was proposed as early as 1970 for a field reversed concept and inertial fusion reactors. The idea was extensively developed during the APEX Project, at the turn of the century, and it is the subject at present of the biennial International Symposium on Lithium Applications (ISLA), whose fourth meeting took place in Granada, Spain at the end of September 2015. While liquid metal flowing concepts were specially addressed in USA research projects, the idea of embedding the metal in a capillary porous system (CPS) was put forwards by Russian teams in the 1990s, thus opening the possibility of static concepts. Since then, many ideas and accompanying experimental tests in fusion devices and laboratories have been produced, involving a large fraction of countries within the international fusion community. Within the EUROFusion Roadmap, these activities are encompassed into the working programs of the plasma facing components (PFC) and divertor tokamak test (DTT) packages.In this paper, a review of the state of the art in concepts based on the CPS set-up for a fusion reactor divertor target, aimed at preventing the ejection of the liquid metal by electro-magnetic (EM) forces generated under plasma operation, is described and required R+D activities on the topic, including ongoing work at CIEMAT specifically oriented to filling the remaining gaps, are stressed.

Development of fast video recording of plasma interaction with a lithium limiter on T-11M tokamak

A new high-speed color camera with interference filters was installed for fast video recording of plasma-surface interaction with а Lithium limiter on the base of capillary-porous system (CPS) in T-11M tokamak vessel. The paper presents the results of the study of tokamak plasma interaction (frame exposure time up to 4μs) with CPS Lithium limiter in a stable stationary phase, unstable regimes with internal disruption and results of processing of the image of the light emission around the probe, i.e. e-folding length for neutral Lithium penetration and e-folding length for Lithium ion flux in SOL region.

Selection of materials for tokamak plasma facing elements based on a liquid tin capillary pore system

Capillary-Pore Systems (CPS) filled by liquid metals are considered as an alternative solution of materials choice for plasma facing component of tokamak reactor. Tin is viewed as one of the candidates for CPS because it has lower corrosiveness than gallium and lower saturated vapour pressure compared to lithium. The corrosion resistance of Mo, Nb and W in pure liquid tin was investigated. The corrosion tests were carried out in the static isothermal conditions at a temperature up to 1050°C. As a result of the corrosion study, it was found that Mo does not corrode in liquid Sn, as opposed to Nb and is compatible with liquid tin in temperatures of up to approx. 1000°C. This allows considering Mo as an alloy base material of the in-vessel tokamak elements based on liquid tin capillary pore systems.

Development of technology for fabrication of lithium CPS on basis of CNT-reinforced carboxylic fabric

The paper describes the analysis of liquid lithium interaction with materials based on carbon, the manufacture technology of capillary-porous system (CPS) matrix on basis of CNT-reinforced carboxylic fabric. Preliminary study of carboxylic fabric wettability with liquid lithium is presented. The development of technology includes: microstructural studies of carboxylic fabric before its CNT-reinforcing; validation of CNT-reinforcing technology; mode validation of CVD-method for CNT synthesize; study of synthesized carbon structures. Preliminary studies of carboxylic fabric wettability with liquid lithium consist in carrying out of experiments at temperatures 673, 773 and 873К in vacuum during long time. The scheme of experimental device for manufacturing of lithium CPS and matrix filling procedure with liquid lithium are presented. The concept of lithium limiter with CPS on basis of CNT-reinforced carboxylic fabric is proposed.

Static arrangement of a capillary porous system (CPS): Modelling

The static arrangement is studied of a thin CPS wafer which is filled from below with a liquid metal. The CPS is modelled as a thin cylindrical disk that is resting on a flat wall. It is in contact with a reservoir that provides liquid lithium. Isothermal conditions are considered and a liquid metal layer is assumed to have been established on top of the CPS and reached an axisymmetric static arrangement. A numerical solution is obtained via the finite element methodology that solves the Young-Laplace equation which incorporates surface tension, gravitational, pressure and electrostatic forces. The layer thickness is predicted at static equilibrium as a function of the imposed pressure drop across the wafer, i.e. between the reservoir and the surrounding medium, and the wetting and dielectric properties of the liquid metal. It is seen that at large reservoir overpressure surface tension balances pressure forces and the liquid metal assumes the form of an almost hemispherical drop of small radius. Gravity is not important in this limit. As the pressure drop decreases the drop assumes an oblate shape and a thin film is gradually formed that entirely covers the CPS and extends onto the wetted rigid substrate. In this range, gravity balances pressure drop and surface tension and the film thickness is on the millimeter range, which is relatively large and has negative implications on the stability of the liquid metal layer as the electric field strength increases. Below a certain pressure drop the film in conjectured to become very thin, on the order of μm, and the disjoining pressure is expected to balance the imposed pressure drop across it. Such static arrangements have been reported in the literature and are favored in terms of stability of the CPS against j→×B→ effects.

TECXY Study of a Liquid Lithium Divertor for DEMO

AbstractDivertor targets made out of a capillary porous system (CPS) filled with liquid lithium, have been proposed as an alternative to standard, solid state plates. In the current work we simulate the DEMO edge plasma in either a standard single‐null or snowflake divertor configuration. Our tool is the 2D code TECXY.Lithium ablated from the target plate surface and released into the plasma is shown here to partially screen the incoming heat flux. Lithium's moderate SOL radiation levels suggest additional seeding to be beneficial. Very high heat fluxes to the divertor need to be avoided, as intensive lithium evaporation might unacceptably pollute the plasma.

Development of lithium and tungsten limiters for test on T-10 tokamak at high heat load condition

Application of a complex of powerful (up to 3 MW) ECR plasma heating in T-10 tokamak is pulled down with a problem of the strong plasma pollution at power input more than 2 MW. For the solution of these problems the new W and Li limiters is developed and prepared to implementation. As it is supposed, application of W as a plasma facing material will allow excluding carbon influx into vacuum chamber. An additional Li limiter arranged in a shadow of W one will be used as a Li source for plasma periphery cooling due to a reradiation on Li that will lead to decrease in power deposition on W limiters. Parameters and design of limiters are presented. Plasma facing surface of a limiter is made of capillary-porous system (CPS) with Li. Porous matrix of CPS (W felt) provides stability of liquid Li surface under MHD force effect and an opportunity of its constant renewal due to capillary forces. The necessary Li flux from a Li limiter surface is estimated for maintenance of normal operation mode of W limiters at ECRH power of 3 MW during 400 ms. It is shown, that upgrade of limiters in tokamak T-10 will allow providing of ECR plasma heating with power up to 3 MW at reasonable Li flux.

Determination of tritium generation and release parameters at lithium CPS under neutron irradiation

This paper describes the main parameters of tritium generation and release from lithium capillary-porous system (CPS) under neutron irradiation at the IVG.1M research reactor. The experiments were carried out using the method of mass-spectrometric registration of released gases and using a specially constructed ampoule device. Irradiation was carried out at different reactor thermal powers (1, 2 and 6 MW) and sample temperatures from 473 to 773K.In the experiments a very small tritium release was detected likely due to its high solubility in liquid lithium. It can be caused by formation of lithium tritide during tritium diffusion to the lithium surface.

Investigation of parameters of interaction of hydrogen isotopes with liquid lithium and lithium capillary-porous system under reactor irradiation

In this study, the effect of reactor irradiation on the processes of interaction of hydrogen with liquid lithium and a lithium capillary-porous system (CPS) is considered. The experiments are carried out by the gas-absorption method with use of a specially designed ampoule device. The results of investigation of the interaction of hydrogen with liquid lithium and a lithium CPS under conditions of reactor irradiation are described; namely, these are the temperature dependences of the rate constant for the interaction of hydrogen with liquid lithium at different reactor powers, the activation energies of the processes, and the pre-exponential factor in the Arrhenius dependence. The effect of increasing absorption of hydrogen by the samples under investigation as a result of the reactor irradiation is fixed. The effect can be explained by increasing mobility of hydrogen in liquid lithium due to hot spots in lithium bulk and the interaction of helium and tritium ions (formed as a result of the nuclear reaction of 6Li with neutron) with a surface hydride film.

A physical model of an ejection suppressed CPS liquid lithium divertor target

A physical model has been developed which includes high temperature liquid lithium evaporation, the expanding motion of the liquid lithium vapour cloud, the shielding effects of the vapour cloud on incident plasma particle bombardments, ejection suppressed analysis and a perpendicular field proposal, and photon radiation, heat flux and transport in the lithium vapour cloud plasma. The engineering outline design scheme and the relevant parameters for the liquid lithium surface divertor target plate configured by discrete tiny capillary arrays have been established. Splashing can be suppressed by utilizing discrete and electrical insulating capillary porous systems (CPSs), since the conductivity among the capillary cells has been cut off by adopting a special kind of ceramic composite material made of a non-conducting and unbreakable composite which is able to withstand high temperatures. The formula to describe the temperature-dependent evaporation power has been derived. The maximum temperature increases of the discrete plasma-facing liquid lithium surface divertor target plate have been compared under the high energy flux deposition of 10 MJ m−2 during a 1 ms time duration with or without evaporation power. The results show that a high surface heat load can be withstood by the designed discrete plasma-facing liquid lithium surface divertor target plate due to violent evaporation. The energy deposition of incident energetic particles and weakly relativistic electrons from the scrape-off layer have been calculated. A laboratory experimental facility to simulate liquid lithium surface interactions with plasma has been set up. Research on lithium evaporation, re-deposition and ejection suppressed experiments under high density linear plasma dumping is ongoing.