Ústav fyziky plazmatu

Nejnovější přírůstky:
2018-03-16
15:47
Properties of hydroxyapatite surface deposited by plasma spray technologies
Matějková, M. ; Čížek, Jan ; Mušálek, Radek ; Dlouhý, I.
The surface properties of hydroxyapatite (HA) deposited on the Ti-6Al-4V substrates by plasma spraying were studied. Two different plasma spray technologies (hybrid plasma spray system (WSP-H) and conventional atmospheric plasma spray technology (APS)) and two various feedstock (suspension for WSP-H and powder for APS) were used for deposition of HA layers potentially suitable for bio-applications. The layers properties (thickness, chemical and phase composition) and coating-substrate interface quality were analyzed. The XRD analysis showed formation of small amount of new phases (TTCP and CaO) in layers deposited by WSP-H. Better coating-substrate interface quality of samples prepared by WSP-H was observed. The results showed the deposition of HA through liquid feedstock via WSP-H as a promising route, complementing the traditional APS powder deposition in the near future.

Úplný záznam
2018-03-09
13:19
Preliminary Measurements of Neutrons From The D-D Reaction in The Compass Tokamak
Dankowski, J. ; Janky, Filip ; Kurowski, A. ; Stöckel, Jan ; Twarog, D.
Recent results of measured fast neutrons created in the D-D reaction on the COMPASS tokamak during ohmic discharges are presented in this paper. Two different type detectors were used during experiment. He-3 detectors and bubble detectors as a support. The measurements are an introduction for neutron diagnostic on tokamak COMPASS and monitoring neutrons during discharges with Neutral Beam Injection (NBI). The He-3 counters and bubble detectors were located in two positions near tokamak vacuum chamber at a distance less than 40 cm to the centre of plasma. The neutrons flux was observed in ohmic discharges. However, analysis of our results does not indicate any clear source of neutrons production during ohmic discharges.

Úplný záznam
2018-03-09
13:19
Microwave reflectometry for density profile and turbulence measurements on the COMPASS tokamak.
Bogár, Ondrej ; Bílková, Petra ; Böhm, Petr ; Hron, Martin ; Pánek, Radomír ; Silva, A. ; Zajac, Jaromír ; Varavin, Mykyta
Microwave reflectometry is an established radar technique to acquire various scientific results in plasma fusion research. Fast electron density profile measurements are crucial for the study of fusion plasmas and the operation of fusion devices. Operation capability and first results of the reflectometry on the COMPASS tokamak are presented in this contribution.

Úplný záznam
2018-03-09
13:19
RE beam generation in MGI disruptions on COMPASS.
Ficker, Ondřej ; Mlynář, Jan ; Macúšová, Eva ; Vlainić, M. ; Weinzettl, Vladimír ; Urban, Jakub ; Čeřovský, Jaroslav ; Farník, Michal ; Markovič, Tomáš ; Papřok, Richard ; Vondráček, Petr ; Imríšek, Martin ; Tomeš, Matěj ; Havlíček, Josef ; Varju, Jozef ; Varavin, Mykyta ; Bogár, Ondrej ; Havránek, Aleš ; Gospodarczyk, M. ; Rabinski, M. ; Jakubowski, M. ; Malinovski, K. ; Zebrowski, J. ; Plyusnin, V. ; Papp, G. ; Pánek, Radomír ; Hron, Martin
In the experiments with the massive gas injection (MGI) triggered disruptions in the COMPASS tokamak, post-disruptive runaway electron (RE) beams are generated occasionally. In this contribution, a relatively large set of discharges from the recent years is analysed in order to improve our understanding of the processes behind the beam generation. It seems that despite the low toroidal field applied in the discharges (typically 1.15 T) the magnetic perturbations may be small enough to allow the acceleration and confinement of the electrons. The influence of the different components and different sections of the frequency spectrum of the magnetic perturbations on the beam generation and RE beam current is examined. Fast visible camera images are also analysed. The relevance of COMPASS runaway electron experiments for large machines is discussed. Moreover, the potential of less common diagnostic tools (Cherenkov detector, vertical ECE, ...) to clarify the role of the pre-disruption fast electron population and the influence of prompt runaway electron losses in the current quench is discussed using the recent test measurements.

Úplný záznam
2018-03-07
15:28
Material design problems of plasma-chemical reactors for disposal perfluorinated compounds
Brožek, Vlastimil ; Březina, Václav ; Mastný, L. ; Kubatík, Tomáš František ; Živný, Oldřich
Reduction of perfluorinated gases emissions from semiconductor industry has recently introduced a serious problem from both technological and economic side. With respect to chemistry of the decomposition reactions the most effective abatement techniques developed up to now consists in the interaction of those gaseous pollutants with several types of plasmas. In the framework of Czech-Taiwanese bilateral project No. 17-10246J 'Decomposition of Perfluorinated Compounds and Fluorinated Ozone Depleting Substances' a new plasmochemical reactor design is to be solved. In this reactor the plasma abatement process consisting of interaction of the plasma generated by unique watter stabilized H-WSP plasma torch at temperatures ranging\nfrom 2000 K up to 25,000 K with the treated gases will be carried out. However, the main product generated in the reactor during the steam plasma abatement process is hydrogen fluoride which causes corrosion of almost every construction material. The aim pursued by the work presented is to search for the materials resistant to exposition of HF even at high temperatures. To investigate corrosion resistance of construction materials with thermal stability within temperature interval 2700-3000 °C titan nitride, boron nitride, and silicon carbide have been selected. The samples of those materials have been prepared by spark plasma sintering method and exposed to concentrated solution of hydrofluoric acid for which corrosion rates have been measured

Úplný záznam
2018-03-07
15:28
Preparation of spheroidized and nano-structural spinels by the SPPS method
Brožek, Vlastimil ; Lukáč, František ; Medřický, Jan ; Mušálek, Radek ; Mašláni, Alan ; Mastný, L. ; Brodil, R.
Solution Precursor Plasma Spraying (SPPS) method, using hybrid water-stabilised plasma torch (WSP®-H), is presented in this study. Precursor, in a form of a solution of inorganic salts, is injected into the plasma jet, where the temperature can reach up to 25 000 K and a series of reactions lead to the formation of spherical sub-micrometric sized particles. The complete process of evaporating the liquid, crystallization, thermic decomposition, melting and recrystallization takes place in few milliseconds before the particles solidify. Melted nanoparticles can be either directly collected in order to obtain ultrafine powders or deposited onto a substrate to form micro-splats and continuous polycrystalline, and often partially amorphous, coatings. The possibility of continuous and discontinuous changes of stoichiometric composition in tetrahedral and octahedral configurations were analysed for the deposits of MgAl2O4, CoAl2O4 and CoFe2O4 spinels. Furthermore, thin colourful coatings of ruby and modified cobalt oxides were deposited onto ceramic and metallic substrates.

Úplný záznam
2018-03-07
15:28
Measuring of Mean Plasma Electrical Conductivity in Anode Area of Plasma Torches with an External Anode
Ondáč, Peter ; Mašláni, Alan ; Hrabovský, Milan
We developed a non-intrusive direct procedure of measuring an average electrical conductivity of a plasma volume in hot anode areas of those plasma torches. For our measurements, we used a high-speed camera, a high-voltage probe, and a hybrid water–argon plasma torch. The measurements were made for various values of ambient pressure, arc electric current, and argon flow rate. The measured plasma conductivity is in agreement with a model, camera observations and indirectly also with spectroscopy measurements. The procedure provides missing experimental data on the average plasma electrical conductivity and estimates average plasma temperature in the anode areas. The procedure can be theoretically used in every plasma torch where the anode arc attachment movement can be observed during a restrike process\n

Úplný záznam
2018-03-07
15:28
FÁZOVÁ STABILITA Y2O3 A W-Y2O3 ZPRACOVANÝCH METODOU MECHANICKÉHO LEGOVÁNÍ.
Illková, Ksenia ; Vilémová, Monika ; Lukáč, František
Kinetika fázových transformací B -> C jak v samotném Y2O3 tak i ve slitině W-xY2O3 je velmi důležitá vzhledem k použití těchto materiálů ve vysokoteplotních aplikacích. Chování vysokotlaké fáze B práškového Y2O3 indukované mletím a vlastnosti kompozitu W-Y2O3 byly studovány pomocí diferenční termální analýzy a rentgenové difrakce. Bylo zjištěno, že fázová stabilita je výrazně závislá na rychlosti ohřevu a na době setrvání na dané teplotě.

Úplný záznam
2018-03-07
15:28
The role of pre-ionization on EUV capillary laser profile.
Štraus, Jaroslav ; Schmidt, Jiří ; Koláček, Karel ; Frolov, Oleksandr
The profile of EUV capillary laser beam was believed to be an annulus and a corresponding theory for its explanation was generally accepted. Nevertheless, our recent detailed observation shows, that the laser profile can be remarkably influenced by the parameters of pre-pulse, serving for working gas pre-ionisation before introduction the main current into the capillary. The examples of possible profile shapes and corresponding parameters are presented.

Úplný záznam
2018-03-07
15:28
Deformation of thin self-standing mask at inhomogeneous irradiation.
Koláček, Karel ; Schmidt, Jiří ; Frolov, Oleksandr ; Štraus, Jaroslav ; Chalupský, Jaromír ; Choukourov, A.
Flatness of the mask is one of key features influencing the quality of image. Among factors that can affect mask flatness belongs inhomogeneous illumination. This does not apply to lithography, but to experiments that use only discrete parts of mask e.g. for nanostructuring or other type of material research. It is shown that even single EUV laser shot (laser wavelength ~46.9 nm, pulse duration ~1.5 ns, focused pulse energy ~20 .mu.J, peak fluency 48 J/cm2) not only deforms the mask, but also changes mask-substrate distance. In our case two kinds of grids (one circular with rectangular windows 7.5x7.5 μm and bars 5 micro m (period 12.5x12.5 micro m), other rectangular with rectangular windows 3.2x1.2 μm and bars 0.8 micro m (period 4x2 micro m)) were attached to PMMA substrate and exposed to one or five superimposed focused laser shots. The mask (grid) deformation was inferred from the changes of diffraction pattern engraved into PMMA.

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