635 research outputs found
Grain boundary segregation in UFG alloys processed by severe plastic deformation
Grain boundary segregations were investigated by Atom Probe Tomography in an
Al-Mg alloy, a carbon steel and Armco\trademark Fe processed by severe plastic
deformation (SPD). In the non-deformed state, the GBs of the aluminium alloy
are Mg depleted, but after SPD some local enrichment up to 20 at.% was
detected. In the Fe-based alloys, large carbon concentrations were also
exhibited along GBs after SPD. These experimental observations are attributed
to the specific structure of GBs often described as "non-equilibrum" in ultra
fine grained materials processed by SPD. The grain boundary segregation
mechanisms are discussed and compared in the case of substitutional (Mg in fcc
Al) and interstitial (C in bcc Fe) solute atoms
Impact of pulsed plasma beam on the thermal erosion and the surface structure of graphite
Among materials prospective as plasmaface
materials for first wall of fusion reactor a
priority is given to the materials with low
atomic number, high threshold for physical
sputtering, high thermal conductivity, low
chemical activity to hydrogen, high thermal
resistance and melting point. According to
modern point of view, preferred plasma-face
materials for tokamaks and future Generation
IV reactors should be based on the carbon,
beryllium and tungsten. Tungsten is one of the
most promising materials for protection of
tokamaks diverter plates
Impact of pulsed plasma beam on the thermal erosion and the surface structure of graphite
Among materials prospective as plasmaface
materials for first wall of fusion reactor a
priority is given to the materials with low
atomic number, high threshold for physical
sputtering, high thermal conductivity, low
chemical activity to hydrogen, high thermal
resistance and melting point. According to
modern point of view, preferred plasma-face
materials for tokamaks and future Generation
IV reactors should be based on the carbon,
beryllium and tungsten. Tungsten is one of the
most promising materials for protection of
tokamaks diverter plates
Strong Field-Induced Frequency Conversion of Laser Radiation in Plasma Plumes: Recent Achievements
New findings in plasma harmonics studies using strong laser fields are reviewed. We discuss recent achievements in the growth of the efficiency of coherent extreme ultraviolet (XUV) radiation sources based on frequency conversion of the ultrashort pulses in the laser-produced plasmas, which allowed for the spectral and structural studies of matter through the high-order harmonic generation (HHG) spectroscopy. These studies showed that plasma HHG can open new opportunities in many unexpected areas of laser-matter interaction. Besides being considered as an alternative method for generation of coherent XUV radiation, it can be used as a powerful tool for various spectroscopic and analytical applications
Precision Measurements of d(d,p)t and d(d,n)^3He Total Cross Sections at Big-Bang Nucleosynthesis Energies
Recent Wilkinson Microwave Anisotropy Probe (WMAP) measurements have
determined the baryon density of the Universe with a precision of
about 4%. With tightly constrained, comparisons of Big Bang
Nucleosynthesis (BBN) abundance predictions to primordial abundance
observations can be made and used to test BBN models and/or to further
constrain abundances of isotopes with weak observational limits. To push the
limits and improve constraints on BBN models, uncertainties in key nuclear
reaction rates must be minimized. To this end, we made new precise measurements
of the d(d,p)t and d(d,n)^3He total cross sections at lab energies from 110 keV
to 650 keV.
A complete fit was performed in energy and angle to both angular distribution
and normalization data for both reactions simultaneously. By including
parameters for experimental variables in the fit, error correlations between
detectors, reactions, and reaction energies were accurately tabulated by
computational methods. With uncertainties around 2% +/- 1% scale error, these
new measurements significantly improve on the existing data set. At relevant
temperatures, using the data of the present work, both reaction rates are found
to be about 7% higher than those in the widely used Nuclear Astrophysics
Compilation of Reaction Rates (NACRE). These data will thus lead not only to
reduced uncertainties, but also to modifications in the BBN abundance
predictions.Comment: 15 pages, 11 figures, minor editorial change
Terahertz wave generation from hyper-Raman lines in two-level quantum systems driven by two-color lasers
Based on spatial-temporal symmetry breaking mechanism, we propose a novel
scheme for terahertz (THz) wave generation from hyper-Raman lines associated
with the 0th harmonic (a particular even harmonic) in a two-level quantum
system driven by two-color laser fields. With the help of analysis of
quasi-energy, the frequency of THz wave can be tuned by changing the field
amplitude of the driving laser. By optimizing the parameters of the laser
fields, we are able to obtain arbitrary frequency radiation in the THz regime
with appreciable strength (as strong as the typical harmonics). Our proposal
can be realized in experiment in view of the recent experimental progress of
even-harmonics generation by two-color laser fields.Comment: 5 pages, 4 figure
Plasma Dynamics Characterization for Improvement of Resonantly Enhanced Harmonics Generation in Indium and Tin Laser-Produced Plasmas
R.A.G. is grateful to H. Kuroda for providing the access to the laser facility. As a Center of Excellence, the Institute of Solid State Physics at the University of Latvia received funding from the European Union’s Horizon 2020 Framework Programme H2020-WIDESPREAD-01-2016-2017-TeamingPhase2 under grant agreement no. 739508, project CAMART².In this study, we characterize the properties of indium and tin laser-induced plasmas responsible for efficient high-order harmonics generation of the ultrashort pulses propagating through these media. The optimally formed plasma was determined using the analysis of the time-resolved variations in the spectral and morphological features of spreading indium and tin plasma components under different regimes of laser ablation. We report the measurements of plasma velocities under different regimes of ablation and correlate them with the optimal delay between the heating and probe laser pulses for the generation of harmonics with the highest yield. Electron temperatures and densities are determined using the integrated and time-resolved spectral measurements of plasmas. The resonance-enhanced harmonics are compared with other harmonics from the point of view of the modulation of plasma characteristics. The harmonics of 800 and 1200–2200 nm lasers and their second-harmonic fields were analyzed at optimal conditions of Sn and In plasma formation. The novelty of this work is the implementation of the diagnostics of the dynamics of plasma characteristics for the determination of the optimal plasma formation for harmonics generation. Such an approach allows for the demonstration of the maximal harmonic yield from the studied plasma and the definition of the various resonance-induced harmonic generation conditions. © 2022 by the authors.European Regional Development Fund (1.1.1.5/19/A/003); Institute of Solid-State Physics, University of Latvia has received funding
from the European Union's Horizon 2020 Framework Programme H2020-WIDESPREAD-01-2016-2017-Teaming Phase 2 under grant agreement No. 739508, project CAMART2
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