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A project is proposed of the complex of diagnostics of the plasma-facing elements of the first wall and divertor of tokamak with reactor technologies (TRT). The main objectives of the complex are control of the integrity of plasma-facing elements, monitoring of the state of the first wall and the thermal flows onto the first wall and divertor targets as well as studies of the physical processes in the material of the first wall during its interaction with plasma. A review of expected effects of interaction of plasma with the plasma-facing elements is given; in the first place, with the tungsten facing of the divertor. Based on the analysis of the methods that were tested at existing tokamaks and methods that are being developed within the framework of the international ITER project, a complex of complementary diagnostics is proposed, which satisfies the TRT tasks. In the paper, a variant of implementation at TRT is discussed of frequency/amplitude modulated laser radar, two-wavelength digital holography, active (laser) and passive IR thermography, diagnostics of fuel build-up based on laser desorption and ablation, and the placement of witness samples. A variant is proposed of the placement of these diagnostics at TRT and their physical integration. [ABSTRACT FROM AUTHOR]

The trapping of helium in tungsten irradiated with He+ ions with an energy of 3 keV and fluence of 1019-1022 He/m2 at room temperature was studied by thermal desorption spectroscopy and scanning electron microscopy. Both as-prepared and recrystallized (at 2000 K for 30 min prior to irradiation) tungsten foils with a thickness of 50 μm were used. It was found that the initial structure of tungsten affects both the dynamics of helium accumulation and the size of defects formed in the process of irradiation and subsequent heating. At low irradiation fluences, helium desorption proceeds primarily at 2000-2500 K in recrystallized tungsten and at 1100-1900 K in as-prepared tungsten samples. At high fluences (higher than 1021 He/m2), a considerable amount of helium is released at low temperatures (starting from 400 K), but a significant fraction of it remains in the samples even after heating to maximum temperatures. Analysis of cross-section of the samples performed after thermal desorption revealed pores 10-75 nm in diameter. The largest pores were formed in the samples that were recrystallized prior to irradiation. [ABSTRACT FROM AUTHOR]

In continuation of a previous study of Li-D films’ interactions with atmospheric gases, dynamics of Li-D codeposit interaction with water vapor was studied. Li-D codeposits very actively react with water vapor, leading to formation of LiOH and release of major part of deuterium. The dynamics of the film mass (thickness of the reacted layer) was well described using a diffusion-based model at the early stage of the reaction and using a combined nucleation-diffusion based model in whole period of time. The most of D remaining in the film after exposure to water vapor is released during a heatup below 550 K, that is attributed to LiOH decomposition and occurs at lower temperatures than in the case of initial Li-D film. [ABSTRACT FROM AUTHOR]

Deuterium release from Li-D films co-deposited on a Mo substrate at room temperature in magnetron discharge was investigated by means of thermal desorption spectroscopy. The deuterium concentration in the films was estimated to be D/Li = (14 ± 4)%. TDS from Li-D films just after co-deposition had a sharp peak at 670–710 K. Exposure of deposited Li-D films in the air at room temperature led to deuterium release. Comparison of release in air, water vapor, nitrogen, and oxygen demonstrated that water plays a major role in deuterium release in the air at low temperatures. [ABSTRACT FROM AUTHOR]

An ultrahigh-vacuum setup for studying the interaction of ions with a solid by the thermodesorption spectroscopy method has been developed. The residual pressure achieved in the setup after heating is <2 × 10−7 Pa (the main component of the residual gas is H2). A sample suspended by two tungsten wires is inserted into the main vacuum chamber through a lock chamber. The sample is heated by thermal radiation from the heater from room temperature to 1600–1700 K. The main features of the setup, the experimental technique, and the calibration of desorption flows are discussed. Examples of results obtained on the setup are presented. [ABSTRACT FROM AUTHOR]

Mock-up of the system for remote monitoring of the accumulation of hydrogen isotopes in the walls of the Globus-M2 tokamak was assembled and tested. The measurements were performed using the LIA-QMS laser diagnostics (laser-induced ablation with registration using quadrupole mass-spectrometry). The data were obtained on the content of hydrogen isotopes in deposits appearing after exposing tungsten collectors to the loads in the volume of the Globus M tokamak. After testing the diagnostics under laboratory conditions, it was mounted at the Globus-M2 facility. In-situ measurements of the content of hydrogen isotopes in the graphite tiles of the tokamak divertor were performed. The possibility of combining the L-IA‑QMS diagnostics with the LIBS (laser-induced emission spectroscopy) diagnostics has been confirmed, in order to obtain information on the composition of the ablated material. In addition, the LIBS method was used for obtaining the deuterium/protium isotopic ratio during measurements in the Globus-M2 facility. [ABSTRACT FROM AUTHOR]

A comparative study of the deuterium content in tungsten-deuterium layers 50, 250, and 750 nm thick co-deposited from a magnetron discharge plasma on molybdenum substrates has been carried out. The measurements were carried out by in vacuo thermal desorption spectroscopy without contact with the atmosphere. Simulation of experimental data in the TMAP7 code has been carried out; concentrations and energies of traps have been obtained at which the best agreement with experiment is achieved. The content of deuterium in the films deposited at a temperature of ~100°C was 3–5 at %. It has been shown that the film thickness does not significantly affect the characteristics of deuterium retention trapping centers, although the shape of the spectra for the thickest films is slightly different. [ABSTRACT FROM AUTHOR]

The paper compares the laser-assisted quadrupole mass spectrometry for two laser pulses (15 ns and 80 ps) for W-D films and Ti–V alloy with deuterium. A technique for the production of samples with high concentrations of trapped deuterium, which makes it possible to obtain a good signal repeatability on a quadrupole mass spectrometer for several laser shots, is presented, which can be used to align a diagnostic laser system. The experimental dependence of the total deuterium yield from the studied materials on the energy density is obtained. The high sensitivity of the technique, as well as a weak dependence on the laser pulse duration, is demonstrated. A significant change in the deuterium concentration in the near-surface layer of the tungsten film during contact with the atmosphere is noted. [ABSTRACT FROM AUTHOR]

Modification of the surface layer and deuterium accumulation in tungsten targets under plasma irradiation in a quasi-stationary plasma accelerator with an intrinsic magnetic field QSPA-T, which reproduces the conditions (plasma thermal load of 0.2-5 MJ/m2, pulse duration of 0.1-1.2 ms) typical of ELM events in ITER, are studied. Using a scanning electron microscope, structure modifications at the surface and in the bulk after deuterium plasma irradiation are analyzed. The observed changes in the near-surface layer are compared with the calculated data on the change in the internal structure of tungsten under intense thermal action obtained as a result of the numerical solution of the heat conduction problem. The total deuterium retention in the samples was measured using thermal desorption spectroscopy, and it was in the range of (3-4) × 1016 particles/cm2 for the samples melted during plasma exposure. These numbers exceed by an order of magnitude the values obtained for samples without traces of melting. [ABSTRACT FROM AUTHOR]

The edge plasma parameters were measured by means of a Mach probe in a lithium experiment on the T-11M tokamak. The angular and radial distributions of the ion saturation current, along with the radial distribution of the electron temperature, were obtained in different modes of tokamak operation. The radial distributions of the electron temperature and ion saturation current in the main operating mode (L-mode) revealed a peak in the scrape-off-layer of the vertical limiter (lithium emitter), which can indicate the formation of a magnetic island in this region. The measured plasma flow velocity along the magnetic field was found to be close to one-half of the ion sound velocity for Li+ ions. [ABSTRACT FROM AUTHOR]

Liquid metal plasma facing components (LMPFC) have shown a potential to supplant solid plasma facing components materials in the high heat flux regions of magnetic confinement fusion reactors due to the reduction or elimination of concerns over melting, wall damage, and erosion. To design a workable LMPFC, one must understand how liquid metal interacts with solid underlying structures. Wetting is an important factor in such interaction, several designs of LMPFC require liquid metal to wet the underlying solid structures. The wetting of lithium compounds (lithium nitride, oxide, and carbonate) by 200 °C liquid lithium at various surface temperature from 230 to 330 °C was studied by means of contact angle measurements. Wetting temperatures, defined as the temperature above which the contact angle is less than 90°, were measured. The wetting temperature was 257 °C for nitride, 259 °C for oxide, and 323 °C for carbonate. Surface tensions of solid lithium compounds were calculated from the contact angle measurements. [ABSTRACT FROM AUTHOR]

A new installation PERMEX for the investigation of ion-driven permeation through metals was designed and built. A metal membrane under investigation separates two high-vacuum chambers. In the implantation chamber, the membrane surface is irradiated with a monoenergetic deuterium ion beam with an incident energy in the interval of 100–3000 eV/D. The ion flux at the surface is in a range of 1013–2×1014 D/cm2 s, the membrane temperature can be varied in the interval of 290–1050 K. The permeating deuterium flux from the outlet membrane surface to the volume of the second chamber (registration chamber) is measured by a quadrupole mass-analyzer. The outlet surface of the membrane can be cleaned by an argon ion beam. To approve the correct work of the setup a number of experiments were performed with Ni membranes. First results of experiments with tungsten membranes are presented. [ABSTRACT FROM AUTHOR]

The radiation dynamics of an adiabatic self-similar expanding spherical plasma plume is considered. It is shown that the radiation intensities evolution strongly depends on the adiabatic index γ. For example, it is proven that the radiation intensity in a highly ionized plasma plume increases over time if γ = 5/3 and has a minimum in time if γ < 5/3. The analytical results are compared to measurements of the radiation from lithium laser-produced plasma. A lithium sample was irradiated by a powerful (42 J/cm2) laser pulse, and radiation of produced lithium plasma was registered by a monochromator. Reasonable agreement with the experiments is reached for γ = 5/4. [ABSTRACT FROM AUTHOR]

Tungsten (W) samples were pre-irradiated with low-energy helium (He) ions with an energy of 80 eV, flux of 1021 He/m2s, at a sample temperature of 1200–1250 K in a inductively coupled plasma (ICP) source facility. Such irradiation conditions led to a formation of a nano-structured surface layer of tungsten, called 'fuzz'. These samples were then irradiated with D 3 + ions with an energy of 2 keV and small doses of 1019 D/m2 at room temperature and in-situ thermal desorption analysis (TDS) was performed. It was found that the main factor determining the deuterium (D) retention in W samples pre-irradiated with helium is the concentration of helium below the surface, namely, the D retention was increased with decreasing the He concentration until the nanostructured W 'fuzz' was removed. The effect of nano-structured tungsten 'fuzz' is only in a decrease of the reflection coefficient of deuterium ions compared to a smoother surface, resulting in the increase of the D influx into W and, consequently, increase of the D retention. However, this increase has a minor effect on the D retention compared to the He concentration in the subsurface layer of W. [ABSTRACT FROM AUTHOR]

Abstract In the present work, helium (He) was incorporated into tungsten (W) samples by inductively coupled plasma (ICP) source above the threshold of He-induced W 'fuzz' formation on W surface. Then, W samples with and without nano-structured W 'fuzz' were exposed to pulsed heat loads using deuterium (D) plasma in quasi-stationary high-current plasma gun QSPA-T. The pulse duration was 1 ms and number of pulses was varied from one to thirty to simulate ITER transient events with surface heat load parameters relevant to edge-localized-mode (ELM) impacts. The irradiation was performed below and above the W melting threshold. The D and He retention in each irradiated sample was measured by a method of thermal desorption spectroscopy. We examined the impact of (i) ELMs-like events and (ii) formation of He-induced nano-structured 'fuzz' on the D retention in W. We found that the D retention was the highest for samples irradiated by plasma gun above the melting threshold after thirty pulses. Moreover, the D retention after 10 pulses of deuterium plasma gun exposure was higher than that after stationary low-energy plasma exposure at sample temperature of either 600 or 700 K indicating the dominate influence of ELM's-like events on the D retention compared to normal operation regime. The D retention in W samples with the presence of He-induced W 'fuzz' was slightly smaller than without that after one pulse of plasma gun exposure with heat load below the W melting temperature. The W 'fuzz' was not disappear in this loading conditions, only the length and thickness of nano-structured W fibres were reduced by factors of ∼4 and ∼2, respectively. The He concentration in W with W 'fuzz' was decreased by a factor of about 3 after one pulse of plasma gun exposure. The results obtained give possibility to assess the particle retention in divertor areas subjected to high thermal loads at different operation regimes. [ABSTRACT FROM AUTHOR]

The concept of the small spherical tokamak project is described, the main objectives of the project are to increase competencies at the University in the training of personnel in the field of physics and technologies of controlled thermonuclear fusion, as well as attracting young people to this area. The implementation of the project also implies giving impetus and new opportunities for improving the methods of plasma diagnostics developed at the University, studies on the plasma surface interactions and computer simulation of processes in the plasma and on the plasma facing surfaces. The installation has a large radius of 25 cm, an aspect ratio of less than 2, and a vertical elongation of ∼ 3, which allows, in principle, for small sizes and costs of the installation, taking into account the subsequent increase in the toroidal field to ∼ 2 T, to carry out important studies for progress in plasma performance in tokamaks. Namely, research on physics of plasma confinement, current drive with RF power and plasma interaction with materials. The project includes a phased implementation with a multiple increase in the magnetic field and plasma current, as well as the possibility of quick and convenient access to the internal elements of the discharge chamber and the simultaneous use of a large number of diagnostics. [ABSTRACT FROM AUTHOR]

Abstract: A numerical model describing deuterium release from metal with pores in the near surface region has been developed and applied for the simulation of the thermal desorption spectra (TDS) of deuterium from tungsten irradiated by D+ ion beam. The experimental TDS peak related to desorption from pores has a maximum at about 630K. By varying parameters of the model, a good agreement between simulation and experiments can be obtained. The factors determining the TDS peak position and shape are discussed. A high temperature tail on experimental TDS data is explained by the distribution of pores and trapped deuterium through the metal. [Copyright &y& Elsevier]