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Fluctuations in the scrape-off layer and edge plasma of the COMPASS tokamak
Seidl, Jakub; Jiráková, Kateřina; Adámek, Jiří; Grover, Ondřej; Horáček, Jan; Hron, Martin; Vondráček, Petr
2018 - English
We have identified two distinct types of turbulent fluctuations in COMPASS plasmas, the high-frequency edge oscillations and low-frequency SOL blobs. The transition region is localized in the near SOL, where both types spatially overlap and interact and the radial particle transport gradually transfers from high to low frequencies. Even though skewness of isat fluctuations is positive even inside LCFS, distinguishable Gamma-distributed PDF, formed by the low-frequency fluctuations, arises in the near SOL. This supports, together with turbulence spreading rate being positive in the near SOL but negative in the edge, the picture presented in [3] that most of the fluctuations that form a positive skewness in the edge region disappear around LCFS and new blobs are formed in the near SOL. Further, we cannot confirm the assumption that the blobs are generated randomly according to a Poisson process. Oscillations of all measured quantities, incl. radial particle flux, in the near SOL are peaked around ∼13 kHz. This seems to correspond to a poloidally rotating structure with a rather large poloidal wave-length ∼ 15 − 20 cm, that at least partly modulates blob generation. Nevertheless, we note that time separation of blobs becomes more random further in the SOL, possibly due to differences in their individual propagation. These observations hold for diverted plasmas, but the situation may be different in limited low-elongation plasmas where the radius of zero skewness was observed to be shifted significantly (several cm) inwards, compared to diverted configuration, and Gamma-like PDF is detected even inside the LCFS. Study of these plasmas is ongoing.
Keywords:
plasma; tokamak; turbulence
Fulltext is available at external website.
Fluctuations in the scrape-off layer and edge plasma of the COMPASS tokamak
We have identified two distinct types of turbulent fluctuations in COMPASS plasmas, the high-frequency edge oscillations and low-frequency SOL blobs. The transition region is localized in the near ...
Effect of sintering temperature on microstructure and mechanical properties of AE42 magnesium alloy prepared by spark plasma sintering
Minárik, P.; Lukáč, František; Cinert, Jakub; Šašek, S.; Král, R.
2018 - English
Magnesium alloy AE42 was prepared by powder metallurgy technique of spark plasma sintering. The effect of sintering parameters, particularly sintering temperature, on the microstructure and mechanical strength was investigated. The gas-atomized powder was sintered at four temperatures in the temperature range of 400-550 °C. It was found that mechanical strength of the sintered samples was significantly affected by several microstructural features. Application of relatively high load during sintering caused deformation of the individual particles and consequent recrystallization depending on the processing temperature resulted in the release of internal strain and in grain growth. As a result, the evolution of the mechanical strength as a function of the sintering temperature was significantly affected by residual stress, grain size and coarsening of secondary phase particles.
Keywords:
Magnesium; Mechanical properties; Microstructure; Spark plasma sintering
Available at various institutes of the ASCR
Effect of sintering temperature on microstructure and mechanical properties of AE42 magnesium alloy prepared by spark plasma sintering
Magnesium alloy AE42 was prepared by powder metallurgy technique of spark plasma sintering. The effect of sintering parameters, particularly sintering temperature, on the microstructure and mechanical ...
OLGA – efficient full wave code for the coupling of LH grills
Preinhaelter, Josef; Hillairet, J.; Urban, Jakub
2018 - English
The full wave code OLGA, for determining the coupling of a single row lower hybrid launcher (waveguide grills) to the plasma, is extended to handle multirow multijunction active passive structures (like the C3 and C4 launchers on TORE SUPRA) by implementing the scattering matrix formalism. The extended code is still computationally fast because of the use of (i) 2D splines of the plasma surface admittance in the accessibility region of the k-space, (ii) high order Gaussian quadrature rules for the integration of the coupling elements and (iii) utilizing the symmetries of the coupling elements in the multiperiodic structures. The extended OLGA code is benchmarked against the ALOHA-1D, ALOHA-2D and TOPLHA codes for the coupling of the C3 and C4 TORE SUPRA launchers for several plasma configurations derived from reflectometry and interferometery. Unlike nearly all codes (except the ALOHA-1D code), OLGA does not require large computational resources and can be used for everyday usage in planning experimental runs. In particular, it is shown that the OLGA code correctly handles the coupling of the C3 and C4 launchers over a very wide range of plasma densities in front of the grill.
Keywords:
lower hybrid waves; coupling; large multirow multijunction grills; tokamak; full-wave
Fulltext is available at external website.
OLGA – efficient full wave code for the coupling of LH grills
The full wave code OLGA, for determining the coupling of a single row lower hybrid launcher (waveguide grills) to the plasma, is extended to handle multirow multijunction active passive structures ...
Collimator - test readiness review
Budasz, Jiří; Kaván, František; Kredba, Jan; Lédl, Vít; Mach, Marek; Pleštil, Jan; Psota, Pavel; Steiger, Lukáš; Tomka, David; Václavík, Jan; Veselý, Martin
2018 - English
This document describes the test procedure applicable to the overall functional test of the NEOSTED collimator.\nThe test to be performed according to this procedure are to demonstrate the compliance of the above item to the requirements specified in the applicable document as part of the overall verification program. The test results shall be collected in a Test Report.
Keywords:
collimator; PLC system; telescope; interferometry
Available at various institutes of the ASCR
Collimator - test readiness review
This document describes the test procedure applicable to the overall functional test of the NEOSTED collimator.\nThe test to be performed according to this procedure are to demonstrate the compliance ...
Technical manual - neosted SOT test bench
Steiger, Lukáš
2018 - English
The purpose of this document is to provide basic set of rules and instructions that allows using and maintaining of the NEOSTED SOT test bench (BB).\nFurther detailed informations and proper references about individual parts of the BB system can be found in [AD-2, AD-3].
Keywords:
test bench; optical testing; collimator; neosted
Available at various institutes of the ASCR
Technical manual - neosted SOT test bench
The purpose of this document is to provide basic set of rules and instructions that allows using and maintaining of the NEOSTED SOT test bench (BB).\nFurther detailed informations and proper ...
Electric probe measurements in the anode area of a DC arc plasma torch at low pressure
Ondáč, Peter; Mašláni, Alan; Hrabovský, Milan
2018 - English
We measured radial profiles of the electric field, plasma electrical potential and electron temperature in the hot anode area of a hybrid water-argon DC arc plasma torch with an external anode. The measurements were made under different values of the ambient pressure, during the restrike mode with a constricted anode arc attachment or during a supersonic mode with a diffuse anode arc attachment. The results provide first experimental data on plasma electrical potential in that anode area.
Keywords:
plasma; arc; anode; low pressure; electric probes
Available at various institutes of the ASCR
Electric probe measurements in the anode area of a DC arc plasma torch at low pressure
We measured radial profiles of the electric field, plasma electrical potential and electron temperature in the hot anode area of a hybrid water-argon DC arc plasma torch with an external anode. The ...
The effect of spark plasma sintering on the porosity and mechanical properties of Ti-15Mo alloy
Terynková, A.; Kozlík, J.; Bartha, K.; Chráska, Tomáš; Dlabáček, Zdeněk; Stráský, J.
2018 - English
Metastable β-titanium alloys are receiving much interest for various applications such as aircraft industry and medicine thanks to their excellent mechanical properties and biocompatibility. The common way of preparing the titanium alloys is hindered by its production costs. Powder metallurgy (PM) approach is a promising route for cost-effective fabrication of titanium alloys due to possibility of near net shaping. In this study, binary biomedical Ti-15Mo alloy was prepared by PM. Gas atomized powder was sintered by spark plasma sintering (SPS) above the β-transus temperature of the studied alloy. The compaction of the powders was accomplished by short-time sintering. The effect of the time of sintering on the porosity and the microhardness in centre part as well as in periphery part of the sample was investigated. The samples revealed significant inhomogeneity the porosity increases with the distance from the centre of the specimen. With increasing sintering times the porosity decreases and simultaneously the microhardness increases.
Keywords:
Metastable β-titanium alloys; Porosity; Powder metallurgy; Spark plasma sintering
Available at various institutes of the ASCR
The effect of spark plasma sintering on the porosity and mechanical properties of Ti-15Mo alloy
Metastable β-titanium alloys are receiving much interest for various applications such as aircraft industry and medicine thanks to their excellent mechanical properties and biocompatibility. The ...
Relativistic effects in plasma produced with sub-nanosecond 3-TW laser
Krása, J.; Klír, Daniel; Řezáč, Karel; Cikhardt, Jakub; Krůs, Miroslav; Velyhan, Andriy; Pfeifer, Miroslav; Dostál, Jan; Dudžák, Roman; Krupka, Michal; Kaufman, J.; Pisarczyk, T.; Kalinowska, Z.; Chodukowski, T.
2018 - English
This contribution deals with observations of relativistic electrons produced in a laser plasma interaction experiment at the PALS laser system operated at the Institute of Plasma Physics in Prague. The PALS laser is a near-infrared 3-TW iodine laser designed to deliver irradiance on target of 1016 Wcm2- in≈300 ps pulses at the wavelength of 1.315 μm. Various foils of 6 500 μm in thickness were irradiated with Iλ2 ≈5×1016 W cm-2 μm2 Under these conditions we have observed relativistic electrons expanding into the vacuum with maximum energy going beyond 4 MeV. The relativistically accelerated forward electrons escaping from the rear target surface were observed with the use of electron energy analysers. The observed electron energy spectra indicate that the applied laser intensity was increased by the thermal and relativistic self-focusing. The application of a unique femtosecond interferometry technique allowed us to observe bunches of thermal electrons occurring in the plasma expanding against the focused laser beam.
Keywords:
laser-produced plasma; relativistic electrons
Fulltext is available at external website.
Relativistic effects in plasma produced with sub-nanosecond 3-TW laser
This contribution deals with observations of relativistic electrons produced in a laser plasma interaction experiment at the PALS laser system operated at the Institute of Plasma Physics in Prague. ...
Test procedure - neosted SOT test bench
Pleštil, Jan; Steiger, Lukáš; Václavík, Jan; Veselý, Martin
2018 - English
This document describes the final design of the NEOSTED SOT Test Bench, i.e. its individual components, and serves as a groundwork for the acceptance test procedure.\nThe test to be performed according to this procedure are to demonstrate the compliance of the above item to the requirements specified in the applicable document [1] as part of the overall verification program. The test results shall be collected in a Test Report.
Keywords:
collimator; optical tests; stage; alignment
Available at various institutes of the ASCR
Test procedure - neosted SOT test bench
This document describes the final design of the NEOSTED SOT Test Bench, i.e. its individual components, and serves as a groundwork for the acceptance test procedure.\nThe test to be performed ...
Fluctuations in the scrape-off layer and edge plasma of the COMPASS tokamak
Seidl, Jakub; Jiráková, Kateřina; Adámek, Jiří; Grover, Ondřej; Horáček, Jan; Hron, Martin; Vondráček, Petr
2018 - English
In this work we study properties of turbulent structures in the scrape-off layer (SOL) and edge plasma of the COMPASS tokamak. Two distinct types of coherent oscillations are observed: a) broadband high frequency branch rotating in the electron diamagnetic direction, appearing mainly in the confined region but protruding also to the SOL b) low-frequency blobs rotating in an opposite poloidal direction, formed in the vicinity of the radius of zero electric field. The transition region is localized in the near SOL, where both types spatially overlap and interact and the radial particle transport gradually transfers from high to low frequencies. Even though skewness of fluctuations of the ion saturation current is positive even inside LCFS, distinguishable Gamma-distributed PDF, formed by the low-frequency fluctuations, arises in the near SOL and most of the fluctuations that form a positive skewness in the edge region disappear around LCFS.
Keywords:
plasma; tokamak; turbulence
Fulltext is available at external website.
Fluctuations in the scrape-off layer and edge plasma of the COMPASS tokamak
In this work we study properties of turbulent structures in the scrape-off layer (SOL) and edge plasma of the COMPASS tokamak. Two distinct types of coherent oscillations are observed: a) broadband ...
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