Capillary Porous System Research Articles

Study of lithium influx, radiation, transport and influence on plasma parameters in the T-10 tokamak

An investigation of lithium influx to plasma, radiation, transport, and its influence on plasma parameters is carried out using spectroscopy and transport modeling methods. The lithium source in the discharge of the T-10 tokamak is a moving Li-limiter based on a tungsten capillary-pore system (CPS). A strong dependence is found between the Li influx to plasma on the distance between the Li-limiter and plasma current boundary in the scrape-off layer (SOL) region. It is shown that if the Li-limiter is located on the radius of the chamber wall (r ≈ 40 cm), lithium influx to plasma is at a low level with a value ∼2·1018 s−1 and the Li nuclei concentration in the plasma does not exceed ∼0.5% of electron density ne with the effective charge value Zeff ≈ 1.2. If the Li-limiter is moved to the current radius (aL = 30 cm), lithium influx to plasma reaches ∼3 · 1020 s−1, which leads to a formation of lithium plasma with the density limit of (the Greenwald density limit) with a Zeff value of ≈2.9 and ≈10% of the remaining deuteron density. In this case, the lithium radiation losses power estimated in Li-plasma is extremely low and does not exceed ≈15% of ohmic power. All obtained results are interpreted using transport models. Changing the lithization level of the chamber walls can significantly reduce the level of C, O, and W impurities and greatly affect the Zeff values. The dependencies of energy confinement times in the electron and ion components on the value of the averaged electron density are investigated in regimes with significantly varying Zeff values. The paper presents the computational analysis of the lithium radiation power at the plasma periphery and in the SOL as a function of boundary conditions, transport characteristics, and confinement times of lithium ions.

Анализ кризиса теплопередачи в капиллярно-пористой системе охлаждения элементов теплоэнергоустановок

A model of dynamics of the vapor bubbles that emerge on solid surfaces of porous structures and the steam generating wall (bottom layer) is presented in this work. The model was filmed and photographed by a high-speed camera SKS-1М. The discharge of high heat flows (up to 2·106 W/m2) was maintained by the joint action of capillary and mass forces with the help of intensifiers. An analytical model was developed based on the theory of thermoelasticity. The limit state of the porous coating with poor thermal conductivity and the metal bottom layer was determined. Heat flows were calculated from the spontaneous birth of the vapour nucleus (10–8) to the material destruction (102–103 s), thus the interval from the process of relaxation to the maximum process (destruction) was described. The size of the pullout particles determined in the model at the moment of porous coating destruction showed good congruence with the experimental data obtained at the optic stand. The destruction of coating under the compression forces occurs much earlier than the tension forces. It is probable that the destruction will happen under the impact of the compression and shear forces. The intervals of the heat flow when such destruction takes place are different for quartz and granite coating. Each thickness of the pullout particles under the impact of compression forces has its limit values of the heat flows, which are located within the mentioned intervals. As the specific heat flow in the heated layer increases and, therefore, the heating time decreases, the impact of the compression stresses increases as well. Despite the high resistance to compression, destruction from the compressive heat tension occurs in more favorable conditions immediately, and in diminutive volumes. Experimental testing units, test conditions, the outcome of the heat exchange crisis, the limit state of the surface and the calculation of critical heat flows are presented. The capillary porous system that works under the joint action of capillary and mass forces is studied. The system has advantages compared to pool boiling, thin-film evaporators and heat pipes.

Experiments with tin liquid-metal capillary porous system in the PLM device

Plasma tests of a tin capillary-porous system (CPS) were carried out on the PLM plasma device. This CPS is made similar to the lithium CPS used in experiments in tokamaks T-10, T-11M. The CPS system was immersed in the PLM plasma device and tested for 3 hours in a stationary helium discharge with plasma load of 1 MW / m2. The tin CPS has not damaged after such plasma load suggesting it as plasma facing component in fusion reactors and plasma engines.

Lithium deposits from the T-10 tokamak after experiments with lithium capillary-porous system

The structure of lithium deposited specimens at the T-10 tokamak vessel after examination of lithium capillary porous system were analysed. Scanning electron microscopy have been used to analyse the deposits. Composites of lithium carbonate LixCOy have been found by analysis. Plasma irradiation of these lithium specimens have been carried out in the PLM plasma device with plasma parameters similar to the tokamak divertor plasma. Stationary plasma load up to 1 MW/m2 during 200 minutes in the PLM provided the change of surface morphology revealed by post-mortem analysis.

Lithium divertor of KTM tokamak

At present time the project of Kazakh material science tokamak KTM is under implementation. In addition to solving problems in the study of materials for fusion technologies on tokamak is working out innovative design elements of the divertor. The design of the lithium divertor module based on lithium capillary-porous systems has been developed and successfully tested under real tokamak conditions. In this design, the solution to the problem of removal of heat flows of high density was implemented through the use of a liquid metal coolant based on the eutectic alloy Na-K. Requirements to improve the safety and compatibility of the design of the divertor with other in-vessel elements of the tokamak, cooled by water, and limiting the temperature of the lithium receiving surface at <600°C at heat flows of 10-20 MW/m2 led to the creation of a new design solution for the experimental module of the divertor and the use of a new coolant – gas dispersed water flow (gas-water spray). The article describes and justifies the design solutions of the new version of the module, the parameters of the coolant and the cooling system scheme. Experimental results on determination of heat transfer coefficient for coolant based on gas-water spray are considered

The Nature of the Supramolecular Structural Variation and Hydrophilic Properties of Cellulose during Water Sorption

Water sorption on cellulose was studied in detail. The mechanism of the adsorption–desoprtion hysteresis loop was considered using NMR relaxation methods and sorption phenomena. The degree of crystallinity was found to decrease in cellulose during water sorption, while the specific surface area of cellulose increased because a wedging pressure arose as a new adsorbent–adsorbate interface formed. The most significant changes in these parameters were observed during desorption and were accompanied by the formation of an additional capillary-porous system in cellulose. Correlations were observed between the surface tension coefficient at the solid–liquid interface, the adsorption equilibrium constant, and the net heat of adsorption.

Application areas and calculation method for capillary-porous heat exchangers of the new heat-removing class

The paper is centered on research focused on the fundamental studies of capillary-porous systems working in the mass forces field. Examined are the effects of pressure, excess fluid, the methods for heating and for supplying coolant, as well as the type of material used, in addition to the intensifier type amongst others, on the integral and thermo-hydraulic characteristics of the heat transfer process. The information obtained from the research can be used in the design, engineering calculations and operation of different energy installations of power plants. Experimentally obtained approximation for the law of the growth of a bubble in a cell of a porous structure, taking into account the influence of underheating, velocity and thermal properties of liquid and a heating surface, was used for determination of the radius of a “dry” spot. The heat transfer control permits to form a new class in the system for heat removing. Devices for heat exchange were built to raise their efficiency, reliability and to be loyal to environment. Capillary-porous heat exchanger shaped as a box provides safety from an explosion. The engineering method for calculation is done for limiting and operational characteristics of capillary-porous heat exchanger. The heat transfer control permits the development of a new class in the system for heat removal. Devices for heat exchange were built with the purpose of increasing both efficiency and dependability in an environmentally conscious manner. A capillary-porous heat exchanger shaped as a box provides protection against an explosion. Obtaining Its limiting and operational characteristics is done by means of an engineering method for calculation.

The investigation of plasma-induced wettability of liquid tin-capillary porous system

Abstract The bias voltage-accelerated plasma was developed to investigate the in-situ wetting between liquid tin (Sn) and capillary porous system (CPS). Low wetting temperature was achieved in comparison to traditional static method. During the plasma irradiation, the correlation among temperature step, optical emission spectrum of Sn atom and wetting phenomenon was disclosed and discussed, which could provide a hint for the wetting criterion of liquid metal-CPS. The results also showed that the wetting of Sn-CPS could maintain the liquid Sn from the MHD effect, while the liquid Sn droplet would be propelled to detach from CPS for the unwetted Sn-CPS.

Methodology of the Experiments to Study Lithium CPS Interaction with Deuterium Under Conditions of Reactor Irradiation

Problems of plasma-facing materials degradation and in-vessel element destructions, tritium accumulation and plasma pollution can be overcome by the use of liquid metals with low atomic number. The best candidate as a material for divertor receiving plates and other in-vessel devices is lithium. One of the problems associated with the use of such lithium systems in the fusion reactors is to determine the parameters of the working gases interaction with plasma facing surfaces under conditions simulating real operation, i.e. under conditions of neutron and gamma radiation. This paper describes a technique of the reactor experiments to study lithium capillary-porous systems (CPS) interaction with deuterium under neutron irradiation. The neutron-physical and thermophysical calculations were the basis for the design development and further manufacture of a unique irradiation ampoule device with a lithium CPS sample. Several experiments were performed to calibrate the deuterium fluxes through experimental cell with lithium CPS; and preliminary results of these experiments were obtained.

Formulized average surface binding energy elevation and lithium vaporization and redeposition investigations in capillary pore systems

An investigation into lithium evaporation and redeposition with multi-mesh capillary pore systems (CPS) has been performed on a one-cathode linear plasma device. A diagnostic system has been used to monitor the lithium evaporation process in the vicinity of the specimen surface, with the adjustable plasma parameters of electron temperature ranging from 0.4–0.9 eV and electron density from 0.8–3.2 × 1019 m−3. The experimental results show that the lithium evaporation rate follows the reduction scaling ratio of 1.94:1.69:1.00 as the number of mesh layers is increased from two to four, which is closely related to the time-dependent fraction weighted average surface binding energy (i.e. evaporation heat) elevation because a fraction of lithium atoms is adhered to the mesh surface. From the viewpoint of nanoscale physics, a new formula is derived for the first time to qualitatively explain the physical mechanism of evaporation heat, or of time-dependent fraction weighted dual average surface binding energy with minor elevation in this special concomitant configuration CPS, which consists of liquid lithium and multi-meshes. The reason for this phenomenon is that the mesh surface binding force acts on a fraction of the adhered lithium atoms, leading to a minor elevation in the evaporation heat. The lithium vapor plays a modest shielding role from the incident heat flux dumping by stopping power plus lithium impurity radiation enhancement, as in the impurity radiation divertor, otherwise the thermal equilibrium of the system could not be attained. In addition, an experimental comparison with a nonactive target and a semi-empirical temperature-dependent model calculation have been applied to further verify the shielding effect. It has been observed that the redeposition rate increases with the applied discharge current.

Behavior of Capillary-Porous Systems with Liquid Lithium under Influence of Pulsed Deuterium Plasma

Capillary-porous systems (CPS) with liquid lithium are considered as a prospective alternative to traditional structural materials (W, Be, CFC) during the production of in-vessel elements contacting plasma of stationary thermonuclear reactors. The behavior of CPS with liquid lithium under the impact of pulsed deuterium plasma flows is considered. The basic processes determining the high stability of CPS against damage are revealed and the critical parameters defining the CPS resistance are specified. The behavior of the tungsten-lithium CPS after its interaction with atmospheric gases is studied in experiments on a plasma facility at the Ioffe Physical-Technical Institute. The irradiated samples of the CPS were studied by optical and scanning electronic microscopy and local X-ray spectral and X-ray diffraction analyses. The surface temperature was measured using a bicolored pyrometer during deuterium plasma irradiation. The outcome of the plasma effect on the heavily oxidized CPS surface substantially differs from that for a pure surface: there is damage to the CPS structure. The specific power of the plasma flow was 22–41 GW/m2, and the number of pulses per irradiated target was 100.

Reactor studies of hydrogen isotopes interaction with lithium CPS using dynamic sorption technique

This paper presents the results of the experiments on hydrogen isotopes interaction with lithium capillary-porous systems (CPS) under reactor irradiation, when sample’s temperatures were from 180 to 550 °C. A special ampoule device with a tubular sample of lithium CPS was developed for experiments. The IVG.1 M reactor (Kurchatov) was used as a source of radiation. The experiments were carried out by the method of dynamic sorption: a constant flow of deuterium was swept through the tube sample with constant degassing and fixation of gas composition in the experimental ampoule device. The paper presents initial data on temperature dependencies of tritium release from lithium CPS under reactor irradiation. The initial analysis showed some features of tritium release: insignificant tritium release in solid lithium (samples temperature below 180 °C), decrease of tritium release under temperature of cell’s center ˜ 250℃, stop of tritium release under temperature of cell’s center ˜ 300℃; then tritium release increased with increase of temperature. The conclusion was made that tritium capture by lithium has a significant influence on the processes of tritium release from lithium CPS under reactor irradiation. The work was performed within the framework of the ISTC #K-2204 project.

Analogy in the processes of heat exchange of capillary-porous coatings in energy installations

A model of the dynamics of steam bubbles generating on a solid surface in porous structures and a steam-generating wall (substrate) is developed. The model is based on the filming and photography with speed camera SKS-1M. The removal of high heat fluxes (up to 2х106 W/m2) is provided by the combined action of capillary and mass forces with application of intensifiers. An analytical model is developed based on the theory of thermoelasticity. The limiting state of a poorly heat-conducting porous coating and a metal substrate has been determined. The heat fluxes were calculated from the time of spontaneous appearance of the steam nucleation (10-8) up to the time of material destruction (102 ÷ 103 s). The destruction of the coating under the action of compression forces occurs in much earlier time than the tension forces. The intervals of the heat flux within which such destruction occurs are different for the quartz coating qmax ≈ 7х107 W/m2, qmin ≈ 8х104 W/m2 and for granite coating qmax ≈ 1х107 W/m2, qmin ≈ 21х104 W/m2. Experimental units, experimental conditions, the results of the heat exchange crisis and the limiting state of the surface are presented, and critical heat fluxes are calculated. The investigated capillary-porous system, operating under the combined action of capillary and mass forces, has the advantage over pool boiling, thin-film evaporators and heat pipes.

Experience in the Development of Liquid Metal Plasma Facing Elements Based on Capillary-Porous Structures for a Steady-State Tokamak (Survey)

Realization of steady-state operation of a fusion reactor requires the development of essentially new designs and materials for plasma facing elements (PFE). The most promising solution in this field is the concept of capillary-porous systems (CPS) with liquid metal (first of all, lithium) that provide PFE surface self-renewal, closed circulation of their corrosion products, and plasma performance improvement and promote achievement of almost stationary modes of plasma burning. Furthermore, the problem of power exhaust with high specific density (20–30 МW/m2) and maintaining a reasonable temperature level on the PFE surface can be solved by the introduction of a special heat removal system. The survey covers the experience in the development, manufacture, and experimental study of liquid metal CPS based on the tests of PFE element models with thermal stabilization systems in steady-state conditions for the T-11М, Т-10, FTU, and КТМ tokamaks and different aspects of liquid metal application.

Generation and transport of atomic lithium during the exposure of liquid metals to hot plasmas in TJ-II

A full campaign of comparative Li/LiSn/Sn testing has been initiated in TJ-II stellarator plasmas. Solid and liquid samples of the three candidates, in a Capillary Porous System (CPS) arrangement, have been exposed to the edge plasma and the associated perturbation on the plasma has been recorded.In this work, only studies on Li and LiSn alloys are reported. The surface temperature of the liquid metal/CPS samples (a tungsten mesh impregnated with SnLi or Li) has been measured during plasma pulses with milliseconds resolution by pyrometry and radial profiles of Li, Li+, and Balmer Hα were recorded together with the electron edge parameters. A simple 1D model, based on the density decay, was applied to the data, allowing for the evaluation of the kinetic energy (Ek) of ejected atomic species while their residence time at the edge was determined by monitoring the ratio of first ion/neutral emission light intensities. Some evolution of Ek with sample temperature was seen for Li atoms, this being likely associated to the different relative contributions of sputtered/evaporated atoms, although values below 0.25 eV were found for sample temperatures above 500 K. The recorded Li+/Li ratios were analyzed through a simple model accounting for several mechanisms for the dispersal of the injected impurity away from the injection location. The same model was applied to injected He atoms (high recycling impurity) in order to check for prompt redeposition of Li.A transition from sputtering driven to evaporation of Li is observed with increasing temperature. Furthermore, no evidence of prompt redeposition is observed in our conditions.

Deuterium retention and erosion in liquid Sn samples exposed to D2 and Ar plasmas in GyM device

The use of tin (Sn) as a liquid metal for plasma facing components has been recently proposed as a solution to the high heat load issue on the divertor target plates in nuclear fusion reactors. Due to its low vapor pressure, low reactivity with hydrogen and good resilience to neutron impact, tin is a good candidate as plasma facing component. However its high atomic number poses concerns about plasma contamination.In this paper two fundamental aspects have been investigated: deuterium retention and erosion fluxes from the Sn surface towards the plasma. The samples were exposed to plasma inside the linear machine GyM in magnetic cusp configuration. This setup permits to expose free liquid specimens without the need for the Capillary Porous System. Moreover it permits to lower the magnetic field in order to increase Sn Larmor radius and consequently limit Sn re-deposition in erosion experiments.Ex-situ analyses by ion beam diagnostics on solid samples exposed to deuterium plasma have proved that the amount of retained atomic deuterium is very low, approximately 0.18 at% estimated by Nuclear Reaction Analysis and 0.25 at% estimated by Elastic Recoil Detection Analysis.In the framework of erosion studies, the spectroscopic parameter S/XB was evaluated in Ar plasma for the SnI line at 380.1 nm by Optical Emission Spectroscopy and mass loss measurements in the 5–11 eV Te range, at a density ne ∼ 1.5 × 1011 cm−3. An average value of 150 ± 23 was obtained.

Experiments on the Capture of Li, H, and D by Lithium Collectors at Different Surface Temperatures at the T-11M Tokamak

Prototypes of lithium emitters and collectors designed on the basis of capillary-porous systems (CPS) are being tried-out at the T-11M tokamak within the concept of continuous lithium circulation, previously proposed for stationary fusion neutron sources (FNSs). One of the goals of the T-11M tokamak research program are to implement the closure of the lithium circulation circuit and to develop the technology of recuperation (extraction and removal from the tokamak chamber) of hydrogen isotopes by using special lithium CPS-based collectors in order to prevent hydrogen isotope accumulation on the inner surface of the discharge chamber. In order to determine the optimal temperature regime for the future FNS operation, the effect of the temperature of the collector surface on its ability to capture lithium and hydrogen isotopes was studied. It is ascertained that the efficiency of capturing lithium and hydrogen isotopes by metal (12Cr18Ni10Ti) collectors in the operating regimes of the T-11M tokamak depends on the temperature of their collecting surfaces; namely, it remains almost constant in the temperature range from–196 to 50°С and then gradually decreases as the temperature rises to 300–400°С. In this case, the amount of the collected lithium is reduced by no more than sixfold, whereas the amount of collected hydrogen isotopes decreases by more than two orders of magnitude. Thus, the wall of a tokamak reactor chamber, which will be heated to 400°С but still coated with residual lithium (or its chemical compounds), will serve as a “mirror” for the incident hydrogen isotopes. It is found that the liquid lithium surface of the CPS-based collector can efficiently capture hydrogen isotopes falling onto it. As the lithium CPS-based collector is heated from 100 to 240°С, the amount of captured deuterium is reduced only twofold. This means that, in a steady-state mode, if, e.g., an MHD pump is used to transport liquid lithium from the collector back to the emitter, then, together with lithium, the captured hydrogen isotopes can also be transported into the recuperation zone.

In-Vessel Devices Based on Capillary-Porous Systems with Liquid Metal for a Stationary Tokamak

The experience gained in developing, creating, and testing prototypes of stationary in-vessel devices based on capillary-porous systems with liquid lithium for the T-11M, T-10, KTM, and FTU tokamaks is presented. A promising scheme is proposed for designing liquid-metal-based in-vessel components with heat removal for thermonuclear reactors of the DEMO type and thermonuclear neutron sources.

Plans for Liquid Metal Divertor in Tokamak Compass

The COMPASS tokamak (R = 0.56 m, a = 0.2 m, BT = 1.3 T, Ip ~ 300 kA, pulse duration 0.4 s) operates in ITER-like plasma shape in H-mode with Type-I ELMs. In 2019, we plan to install into the divertor a test target based on capillary porous system filled with liquid lithium/tin. This single target will be inclined toroidally in order to be exposed to ITER-relevant surface heat flux (20 MW/m2). Based on precisely measured actual heat fluxes, our simulations predict (for 45° inclination, without accounting for the lithium vapor shielding) the surface temperature rises up to 700°C within 120 ms of the standard ELMy H-mode heat flux with ELM filaments reaching hundreds MW/m2. Significant lithium vaporization is expected. The target surface will be observed by spectroscopy, fast visible and infrared cameras. The scientific program will be focused on operational issues (redeposition of the evaporated metal, ejection of droplets, if any) as well as on the effect on the plasma physics (improvement of plasma confinement, L–H power threshold, Zeff, etc.). After 2024, a closed liquid divertor may be installed into the planned COMPASS Upgrade tokamak (R = 0.84 m, a = 0.3 m, BT = 5 T, Ip = 2 MA, Pin = 8 MW, pulse duration ~2 s) with ITER-relevant heat fluxes loading the entire toroidal divertor.

INVESTIGATION OF A HIGH-FORCED COOLING SYSTEM FOR THE ELEMENTS OF HEAT POWER INSTALLATIONS

The studies of the ultimate thermal flows have been carried out in metallic and poorly heat-conducting porous structures, which operate when gravitational and capillary forces act jointly and cool various devices of thermal power plants in order to create a scientific methodology. The mechanism of destruction of metal vaporizing surfaces and poorly heat-conducting coatings of low porosity made of natural mineral media (granite) has been described on the basis of the problem of thermoelasticity and experimental data. Thermal flow dependences on time of their action and depth of penetration of temperature perturbations were identified based on analogy. Capillary-porous systems have high intensity, heat transport ability, reliability, compactness. The results of calculations and experiment showed that the maximum thickness of the particles that detach under the influence of compression forces for granite coatings is (0.25÷0.3).10-2 m. Sections of compression curves that determine the detachment of particles with dimensions of more than 0.3·10-2 m for large thermal flows and short feed times, are screened by the melting curve, and in the case of small thermal flows and time intervals - the expansion curve.