Персона: Гаспарян, Юрий Микаэлович
Email Address
Birth Date
Статус
Руководитель научной группы -Международный центр ядерных компетенций (МЦЯДКОМ)
Фамилия
Имя
Имя
Результаты поиска
The Project of MEPhIST Tokamak
© 2019, Pleiades Publishing, Ltd.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.
Helium retention in tungsten irradiated with He+ ion beam at elevated temperatures
© 2019Helium (He) retention in re-crystallized tungsten (W) irradiated with He+ ions at elevated temperatures (700–1200 K) and fluences in the range of 1020–1022 He/m2 was investigated by means of thermal desorption spectroscopy (TDS). Corresponding surface modifications were analyzed by scanning electron microscopy. Blisters were observed after irradiation at 700 and 1000 K, while the increase of the irradiation temperature up to 1200 K led to development of a complex sponge-like structure on the W surface. Significant surface transformations correlated with appearance of low temperature peaks in TDS spectra below the irradiation temperature. Possible mechanisms and explanations are discussed.
A setup for study of co-deposited films
© 2020 IOP Publishing Ltd and Sissa Medialab.A setup for investigation of thermal desorption spectra of gases accumulated in thin films deposited by plasma sputtering of solid targets is described. Deposition and thermal desorption spectroscopy (TDS) are performed in two different vacuum chambers separated by a gate valve with the sample transferred between the chambers in-vacuo. The temperature of the substrate for deposited films can be varied in the range of 300-800 K; and the deposition rate is controlled by a quartz microbalance. Thermal desorption of co-deposited gases is analyzed by a quadrupole mass spectrometer. Sputtering rate and evaporation of the film during TDS are measured by quartz microbalances. Three experiments are described 1) trapping of deuterium by the growing chemically active Li film with subsequent decomposition and evaporation of the film, 2) temperature dependent deuterium trapping in the growing W film resulting in trapping with several binding energies, and 3) chemical interaction of D-Li layer with water vapor leading to isotopic H-D exchange and chemical transformation of the deposited film.
Isotope exchange in Li-D co-deposited layers at temperatures below 200 °C
© 2020 Elsevier B.V.Hydrogen-deuterium isotope exchange in Li-D co-deposited films was studied as a method of removal of heavy hydrogen isotopes from Li films deposited in fusion devices. The total H and D retention was measured using in-vacuo thermal desorption spectroscopy. Co-deposited Li-D films were kept in H2 gas at 1 Pa and 105 Pa at room temperature, 100 °C, and 200 °C. Some reduction of the D content was observed even at RT, while nearly full isotope substitution was achieved at 200 °C after 1 day at 105 Pa in H2 gas.
Deuterium and helium retention in W with and without He-induced W ‘fuzz’ exposed to pulsed high-temperature deuterium plasma
© 2018 Elsevier B.V. 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.
Temperature dependence of hydrogen co-deposition with metals
© 2019 Elsevier B.V. The deuterium retention in aluminum and molybdenum films co-deposited in magnetron discharge has been measured in a wide range of substrate temperatures (from RT to 800 K) by means of thermal desorption spectroscopy. A multi-step temperature dependence was observed, which was compared with the diffusion based model and previous experimental data for tungsten films. The key role of lattice defects in deuterium trapping was demonstrated. The highest D retention among the investigated materials was observed in W films, which have the lowest H solubility, but the highest binding energies of hydrogen with defects. The detrapping energies and concentrations of defects in the films were estimated on the base of the model, and the energies are consistent with the data for bulk materials.
Retention of Deuterium in the Surface Layers of Tungsten Preliminarily Irradiated with Helium Ions
© 2020, Allerton Press, Inc.Abstract: The retention of deuterium in tungsten preliminarily irradiated with helium ions is investigated by means of thermal desorption spectroscopy (TDS). Preliminary irradiation is performed with a He+ ion beam having an energy of 3 keV and fluence ranging in the interval 1019–1021 He m−2, in order to produce a defect structure typical of different degrees of damage. The specimens are then irradiated with D+3 ions having an energy of 2 keV and a weak fluence of 1019 D m−2, with subsequent TDS analysis to characterize the interaction between deuterium and helium-induced defects. It is shown that an increase in the deuterium retention is observed as soon as irradiation with the minimal fluence of helium ions, but it falls to the background level at fluences above 5 × 1021 He m−2.
Surface Structure Modification and Deuterium Retention in Tungsten under Pulsed Plasma Loads
© 2019, Pleiades Publishing, Ltd.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.
Influence of plasma heat loads relevant to ITER transient events on deuterium retention in tungsten
Deuterium (D) retention in Tungsten (W) under plasma heat loads relevant to edge localized modes in ITER was experimentally investigated at the QSPA-T plasma gun facility. Samples were exposed to 1.0 ms D plasma pulses with different heat loads in the range of 0.4-3.7 MJm(-2) (heat flux factor P root t = 13.3-123 MJm(-2)s(-0.5)). A significant D retention was observed already after one pulse. Moreover, the D retention grew up continuously with increasing the power load, although the surface was melted at highest loads (above 1.4 MJ m(-2)). The D retention was higher than that in the case of stationary plasma irradiation at 600-700 K, indicating possible significant contribution of ELM's-like events to the total D retention. All stages of the experiments (irradiation, storage time and TDS) have been simulated using the TMAP 7 code.
Helium retention in tungsten under plasma and ion beam irradiation and its impact on surface morphology
Helium (He) is a product of deuterium-tritium (DT)-fusion reaction and will be a natural impurity in DT plasma in future fusion devices. He retention in tungsten irradiated by plasma and mass-separated ions in a wide temperature range (300-1200 K) was investigated by means of thermal desorption spectroscopy (TDS). He retention did not exceed the level of 1.5 x 10(21) He m(-2) for all investigated samples. A significant effect of air exposure on TDS spectra was demonstrated. In contrast to in situ TDS measurements, He release after interaction with the air started from similar to 400 K, even in the case of high temperature irradiation. Changes in surface morphology were analyzed by secondary electron microscopy. Blisters were found at the surface after ion irradiation at low temperatures. Acceleration of surface modification and more complex surface morphology was observed in the case of irradiation at temperatures above 1000 K.