| 1. |
- Reimerdes, H., et al.
(author)
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Overview of the TCV tokamak experimental programme
- 2022
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In: Nuclear Fusion. - : IOP Publishing. - 1741-4326 .- 0029-5515. ; 62:4
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Journal article (peer-reviewed)abstract
- The tokamak a configuration variable (TCV) continues to leverage its unique shaping capabilities, flexible heating systems and modern control system to address critical issues in preparation for ITER and a fusion power plant. For the 2019-20 campaign its configurational flexibility has been enhanced with the installation of removable divertor gas baffles, its diagnostic capabilities with an extensive set of upgrades and its heating systems with new dual frequency gyrotrons. The gas baffles reduce coupling between the divertor and the main chamber and allow for detailed investigations on the role of fuelling in general and, together with upgraded boundary diagnostics, test divertor and edge models in particular. The increased heating capabilities broaden the operational regime to include T (e)/T (i) similar to 1 and have stimulated refocussing studies from L-mode to H-mode across a range of research topics. ITER baseline parameters were reached in type-I ELMy H-modes and alternative regimes with 'small' (or no) ELMs explored. Most prominently, negative triangularity was investigated in detail and confirmed as an attractive scenario with H-mode level core confinement but an L-mode edge. Emphasis was also placed on control, where an increased number of observers, actuators and control solutions became available and are now integrated into a generic control framework as will be needed in future devices. The quantity and quality of results of the 2019-20 TCV campaign are a testament to its successful integration within the European research effort alongside a vibrant domestic programme and international collaborations.
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| 2. |
- Kann, D. A., et al.
(author)
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THE AFTERGLOWS OF SWIFT-ERA GAMMA-RAY BURSTS. I. COMPARING PRE-SWIFT AND SWIFT-ERA LONG/SOFT (TYPE II) GRB OPTICAL AFTERGLOWS
- 2010
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In: Astrophysical Journal. - 0004-637X .- 1538-4357. ; 720:2, s. 1513-1558
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Journal article (peer-reviewed)abstract
- We have gathered optical photometry data from the literature on a large sample of Swift-era gamma-ray burst (GRB) afterglows including GRBs up to 2009 September, for a total of 76 GRBs, and present an additional three pre-Swift GRBs not included in an earlier sample. Furthermore, we publish 840 additional new photometry data points on a total of 42 GRB afterglows, including large data sets for GRBs 050319, 050408, 050802, 050820A, 050922C, 060418, 080413A, and 080810. We analyzed the light curves of all GRBs in the sample and derived spectral energy distributions for the sample with the best data quality, allowing us to estimate the host-galaxy extinction. We transformed the afterglow light curves into an extinction-corrected z = 1 system and compared their luminosities with a sample of pre-Swift afterglows. The results of a former study, which showed that GRB afterglows clustered and exhibited a bimodal distribution in luminosity space, are weakened by the larger sample. We found that the luminosity distribution of the two afterglow samples (Swift-era and pre-Swift) is very similar, and that a subsample for which we were not able to estimate the extinction, which is fainter than the main sample, can be explained by assuming a moderate amount of line-of-sight host extinction. We derived bolometric isotropic energies for all GRBs in our sample, and found only a tentative correlation between the prompt energy release and the optical afterglow luminosity at 1 day after the GRB in the z = 1 system. A comparative study of the optical luminosities of GRB afterglows with echelle spectra (which show a high number of foreground absorbing systems) and those without, reveals no indication that the former are statistically significantly more luminous. Furthermore, we propose the existence of an upper ceiling on afterglow luminosities and study the luminosity distribution at early times, which was not accessible before the advent of the Swift satellite. Most GRBs feature afterglows that are dominated by the forward shock from early times on. Finally, we present the first indications of a class of long GRBs, which form a bridge between the typical high-luminosity, high-redshift events and nearby low-luminosity events (which are also associated with spectroscopic supernovae) in terms of energetics and observed redshift distribution, indicating a continuous distribution overall.
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| 3. |
- Andreeva, M. A., et al.
(author)
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Polarization selection in Mössbauer reflectivity for magnetic multilayer investigation
- 2019
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In: VII Euro-Asian Symposium on Trends In Magnetism. - : IOP Publishing.
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Conference paper (peer-reviewed)abstract
- Mossbauer reflectivity experiment with polarization selection are reported. The use of the LiF polarization analyzer allows us to get the pi ->sigma' peak on the reflectivity curve at the critical angle and Mossbauer pi ->sigma' reflectivity spectra of reasonable quality at the critical angle and also at the Bragg angles of superlattice. The impressive difference of the reflectivity spectra measured near the critical angle with and without polarizations analysis is observed for [Fe-57(10)/V-10](20) multilayer characterizing by the ferromagnetic interlayer coupling. The combined fit of the whole set of spectra measured at different angles reveals the existence of antiferromagnetic Fe oxide phases in the top three bilayers. The experiment demonstrates benefits of the Mossbauer reflectivity with polarization analysis in ultrathin surface layer investigations.
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| 4. |
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| 5. |
- Karimov, A. R., et al.
(author)
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A new class of exact solutions for Vlasov-Poisson plasmas
- 2016
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In: Physica Scripta. - : IOP PUBLISHING LTD. - 0031-8949 .- 1402-4896. ; 91:11, s. 114002-
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Journal article (peer-reviewed)abstract
- A new class of exact solutions of the Vlasov-Poisson equations based on the Jeans theorem is considered. The self-consistent solutions for the evolution of the system from given initial particle distributions make use of particular invariants of particle motion with predetermined spatial structure. The relation between the time-dependent coefficients of the latter and the macroscopic plasma quantities, or moments of the distribution function, are obtained. As an illustration, the evolution of an expanding plasma with oscillations of the electron and ion expansion fronts is presented.
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| 6. |
- Karimov, A R, et al.
(author)
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Asymmetric oscillatory expansion of a cylindrical plasma
- 2013
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In: Journal of Plasma Physics. - : Cambridge University Press. - 0022-3778 .- 1469-7807. ; 79:6, s. 1007-1009
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Journal article (peer-reviewed)abstract
- Asymmetric oscillatory expansion of a cylindrical plasma layer into vacuum is investigated analytically by solving the fluid equations of the electrons and ions together with the Maxwell's equations. For the problem considered, it is found that the asymmetrical flow components are strongly affected by the symmetrical components, but not the vice versa.
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| 7. |
- Karimov, A R, et al.
(author)
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Coupled azimuthal and radial flows and oscillations in a rotating plasma
- 2009
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In: PHYSICS OF PLASMAS. - : AIP Publishing. - 1070-664X .- 1089-7674. ; 16:6, s. 062313-
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Journal article (peer-reviewed)abstract
- Nonlinear coupling between the radial, axial, and azimuthal flows in a cold rotating plasma is considered nonperturbatively by first constructing a basis solution for a rotating flow. Simple but exact solutions that describe an expanding plasma with oscillatory flow fields are then obtained. These solutions show that the energy in the radial and axial flow components can be transferred to the azimuthal component but not the vice versa. Nonlinear electron velocity oscillations in the absence of electron density oscillations at the same frequency are shown to exist.
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| 8. |
- Karimov, A R, et al.
(author)
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Coupled flows and oscillations in asymmetric rotating plasmas
- 2009
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In: PHYSICS OF PLASMAS. - : AIP Publishing. - 1070-664X .- 1089-7674. ; 16:10, s. 102303-
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Journal article (peer-reviewed)abstract
- Nonlinear coupling among the radial, axial, and azimuthal flows in an asymmetric cold rotating plasma is considered nonperturbatively. Exact solutions describing an expanding or contracting plasma with oscillations are then obtained. It is shown that despite the flow asymmetry the energy in the radial and axial flow components can be transferred to the azimuthal component but not the vice versa, and that flow oscillations need not be accompanied by density oscillations. (C) 2009 American Institute of Physics. [doi: 10.1063/1.3247875]
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| 9. |
- Karimov, A. R., et al.
(author)
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Dynamics of charged aerosols relevant to transmission of airborne infections
- 2022
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In: Physica Scripta. - : IOP Publishing Ltd. - 0031-8949 .- 1402-4896. ; 97:8
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Journal article (peer-reviewed)abstract
- A simple model including the effects of initial velocity, air drag, gravity, and electrostatics on the dynamics of airborne droplets emitted from humans is presented. It is found that relatively large droplets can also travel far if their charge and/or the atmospheric electric field is sufficiently large.
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| 10. |
- Karimov, A. R., et al.
(author)
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Expansion of a cold non-neutral plasma slab
- 2014
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In: Physics of Plasmas. - : AIP Publishing. - 1070-664X .- 1089-7674. ; 21, s. 122304-
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Journal article (peer-reviewed)abstract
- Expansion of the ion and electron fronts of a cold non-neutral plasma slab with a quasi-neutral core bounded by layers containing only ions is investigated analytically and exact solutions are obtained. It is found that on average, the plasma expansion time scales linearly with the initial inverse ion plasma frequency as well as the degree of charge imbalance, and no expansion occurs if the cold plasma slab is stationary and overall neutral. However, in both cases, there can exist prominent oscillations on the electron front.
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| 11. |
- Karimov, A R, et al.
(author)
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Large quasineutral electron velocity oscillations in radial expansion of an ionizing plasma
- 2012
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In: Physics of Plasmas. - : American Institute of Physics (AIP). - 1070-664X .- 1089-7674. ; 19:9, s. 092118-
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Journal article (peer-reviewed)abstract
- Radial expansion of an ionizing gas or plasma cylinder into vacuum is investigated. An exact model for the evolution of the density and velocity fields of the electrons, ions, and neutrals, including the effect of photo and electron-impact ionization on the flow characteristics is developed and solutions obtained. A quasineutral nonlinear electrostatic mode involving rapid oscillations in the electron velocity but not in the density can occur in the expanding plasma. The mode turns out to be almost unaffected by weak ionization.
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| 12. |
- Karimov, A. R., et al.
(author)
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Properties and evolution of anisotropic structures in collisionless plasmas
- 2016
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In: Journal of Plasma Physics. - : CAMBRIDGE UNIV PRESS. - 0022-3778 .- 1469-7807. ; 82
-
Journal article (peer-reviewed)abstract
- A new class of exact electrostatic solutions of the Vlasov-Maxwell equations based on the Jeanss theorem is proposed for studying the evolution and properties of two-dimensional anisotropic plasmas that are far from thermodynamic equilibrium. In particular, the free expansion of a slab of electron-ion plasma into vacuum is investigated.
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| 13. |
- Karimov, A. R., et al.
(author)
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The processes of nonequilibrium exchange in rotating plasma flows
- 2016
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In: II CONFERENCE ON PLASMA & LASER RESEARCH AND TECHNOLOGIES. - : IOP Publishing.
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Conference paper (peer-reviewed)abstract
- The mechanisms of energy/momentum exchange in rotating and compressing plasma flows have been discussed. It has been shown that such flows are capable of transforming the energy of different degrees of freedom into the energy of one degree owing to the interaction of the coupled nonlinear radial, axial and azimuthal electron-ion oscillations. These processes may lead to the additional acceleration of the flow in azimuthal or axial direction so they might be instrumental for the creation of space thrusters employing pulse transformations for propulsion.
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| 14. |
- Wang, You-Mei, et al.
(author)
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Evolution of a Cold Non-neutral Electron-Positron Plasma Slab
- 2016
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In: Chinese Physics Letters. - : IOP PUBLISHING LTD. - 0256-307X .- 1741-3540. ; 33:8, s. 085205-
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Journal article (peer-reviewed)abstract
- Evolution of a non-neutral cold electron-positron plasma slab is investigated. Initially the slab consists of a quasineutral plasma core bounded on both sides by layers containing only positrons (or electrons). Results from a nonperturbative, or mathematically exact, analysis of the governing fluid conservation equations and the Poisson equation show that despite their equal mass and charge magnitude, the electron and positron fronts can expand separately as well as a single fluid, and that nonlinear surface oscillations can be excited on the expansion fronts.
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| 15. |
- Zhang, Wenmin, et al.
(author)
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Energy coupling among the degrees of freedom in an electron-positron plasma
- 2010
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In: JOURNAL OF PLASMA PHYSICS. - : Cambridge University Press. - 0022-3778. ; 76, s. 329-335
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Journal article (peer-reviewed)abstract
- Nonlinear coupling of the motion in the three spatial degrees of freedom of a cold fluid electron-positron plasma is investigated. Exact, solutions describing expanding flows with oscillations are obtained. It is found that the energy in the irrotational flow component is in general transferred to the rotational components, but not in the reversed direction. Furthermore, since the density evolution need not be related to all the three flow components, oscillations in one or two of the flow fields can be purely electromagnetic and are not accompanied by density oscillations.
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| 16. |
- Zhang, Wenmin, et al.
(author)
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Intense oscillations in the expansion of an inhomogeneous cylindrical electron-positron layer
- 2013
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In: Physica Scripta. - : Institute of Physics. - 0031-8949 .- 1402-4896. ; 88:5, s. 055501-
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Journal article (peer-reviewed)abstract
- Large amplitude oscillations in the expansion of a cylindrical electron-positron plasma layer are investigated. The cold fluid equations and the Poissons equation are solved non-perturbatively in order to allow for very large amplitude oscillations. It is found that oscillations are self-excited during the expansion and can grow to very large amplitudes as the expansion slows down with time and the plasma density decreases. The kinetic energy of the expansion is thereby converted into that of the oscillations.
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