| 57221. |
- Buyanova, M., et al.
(author)
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Different saturation regimes of multipactor between parallel metal plates
- 2008
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In: Proceedings of the 7th International Workshop “Strong microwaves: Sources and Applications, Nizhny Novgorod, Russia, July 27 – Aug. 2, 2008, Institute of Applied Physics, Russian Academy of Sciences. ; :paper T41, s. 143-
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Conference paper (peer-reviewed)
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| 57222. |
- Buyanova, M., et al.
(author)
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Influence of secondary emission yield on the saturation of two-sided multipactor
- 2008
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In: MULCOPIM08, 23-26 September 2008, Valencia, Spain, European Space Agency, Nordwijk, The Netherlands, available on CD. ; , s. paper MP5-6
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Conference paper (peer-reviewed)
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| 57223. |
- Buyanova, M., et al.
(author)
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Influence of secondary emission yield on the saturation properties of multipactor discharges between two parallel metal plates
- 2010
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In: Physics of Plasmas. - : AIP Publishing. - 1089-7674 .- 1070-664X. ; 17:4, s. 043504 -
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Journal article (peer-reviewed)abstract
- A detailed numerical simulation analysis is made of the saturation stage of multipactor discharges between two infinite parallel metal plates in vacuum exposed to a rf voltage. The main physical effect causing saturation of the multipactor discharge is increased space charge, as the electron density becomes large. It is found that the properties of the saturation stage depend crucially on the value of the secondary emission yield of the metal surfaces. Below a certain threshold value, the discharge has a two-sided character, but at this threshold the discharge makes an abrupt transition into two decoupled single-sided multipactor discharges containing significantly increased electron densities. The result of the numerical simulations gives a good picture of the saturation properties of the multipactor discharge and is also supplemented by an approximate analytical investigation that highlights and explains the characteristic properties of the observed saturation behavior.
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| 57224. |
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| 57225. |
- Bychkov, Vitaly, 1968-, et al.
(author)
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The Rayleigh-Taylor instability in inertial fusion, astrophysical plasma and flames
- 2007
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In: Plasma Physics and Controlled Fusion. - 1361-6587 .- 0741-3335. ; 49:12B, s. B513-B520
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Journal article (peer-reviewed)abstract
- Previous results are reviewed and new results are presented on the Rayleigh-Taylor instability in inertial confined fusion, flames and supernovae including gravitational and thermonuclear explosion mechanisms. The instability couples micro-scale plasma effects to large-scale hydrodynamic phenomena. In inertial fusion the instability reduces target compression. In supernovae the instability produces large-scale convection, which determines the fate of the star. The instability is often accompanied by mass flux through the unstable interface, which may have either a stabilizing or a destabilizing influence. Destabilization happens due to the Darrieus-Landau instability of a deflagration front. Still, it is unclear whether the instabilities lead to well-organized large-scale structures (bubbles) or to relatively isotropic turbulence (mixing layer)
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| 57226. |
- Bykov, A. M., et al.
(author)
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Microphysics of Cosmic Ray Driven Plasma Instabilities
- 2013
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In: Space Science Reviews. - : Springer Science and Business Media LLC. - 0038-6308 .- 1572-9672. ; 178:2-4, s. 201-232
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Research review (peer-reviewed)abstract
- Energetic nonthermal particles (cosmic rays, CRs) are accelerated in supernova remnants, relativistic jets and other astrophysical objects. The CR energy density is typically comparable with that of the thermal components and magnetic fields. In this review we discuss mechanisms of magnetic field amplification due to instabilities induced by CRs. We derive CR kinetic and magnetohydrodynamic equations that govern cosmic plasma systems comprising the thermal background plasma, comic rays and fluctuating magnetic fields to study CR-driven instabilities. Both resonant and non-resonant instabilities are reviewed, including the Bell short-wavelength instability, and the firehose instability. Special attention is paid to the longwavelength instabilities driven by the CR current and pressure gradient. The helicity production by the CR current-driven instabilities is discussed in connection with the dynamo mechanisms of cosmic magnetic field amplification.
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| 57227. |
- Bykov, A. M., et al.
(author)
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Microphysics of Cosmic Ray Driven Plasma Instabilities
- 2014
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In: Microphysics of Cosmic Plasmas. - Dordrcht : Springer. - 9781489974136 - 9781489974129 ; , s. 125-156
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Book chapter (peer-reviewed)abstract
- Energetic nonthermal particles (cosmic rays, CRs) are accelerated in supernova remnants, relativistic jets and other astrophysical objects. The CR energy density is typically comparable with that of the thermal components and magnetic fields. In this review we discuss mechanisms of magnetic field amplification due to instabilities induced by CRs. We derive CR kinetic and magnetohydrodynamic equations that govern cosmic plasma systems comprising the thermal background plasma, comic rays and fluctuating magnetic fields to study CR-driven instabilities. Both resonant and non-resonant instabilities are reviewed, including the Bell short-wavelength instability, and the firehose instability. Special attention is paid to the longwavelength instabilities driven by the CR current and pressure gradient. The helicity production by the CR current-driven instabilities is discussed in connection with the dynamo mechanisms of cosmic magnetic field amplification.
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| 57228. |
- Bykov, Igor, 1986-
(author)
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Experimental studies of materials migration in magnetic confinement fusion devices : Novel methods for measurement of macro particle migration, transport of atomic impurities and characterization of exposed surfaces
- 2014
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Doctoral thesis (other academic/artistic)abstract
- During several decades of research and development in the field of Magnetically Confined Fusion (MCF) the preferred selection of materials for Plasma Facing Components (PFC) has changed repeatedly. Without doubt, endurance of the first wall will decide research availability and lifespan of the first International Thermonuclear Research Reactor (ITER). Materials erosion, redeposition and mixing in the reactor are the critical processes responsible for modification of materials properties under plasma impact. This thesis presents several diagnostic techniques and their applications for studies of materials transport in fusion devices. The measurements were made at the EXTRAP T2R Reversed Field Pinch operated in Alfvén laboratory at KTH (Sweden), the TEXTOR tokamak, recently shut down at Forschungszentrum Jülich (Germany) and in the JET tokamak at CCFE (UK). The main outcomes of the work are:Development and application of a method for non-destructive capture and characterization of fast dust particles moving in the edge plasma of fusion devices, as well as particles generated upon laser-assisted cleaning of plasma exposed surfaces. Advancement of conventional broad beam and micro ion beam techniques to include measurement of tritium in the surfaces exposed in future D-T experiments. Adaption of the micro ion beam method for precision mapping of non uniform elements concentrations on irregular surfaces. Implementation of an isotopic marker to study the large scale materials migration in a tokamak and development of a method for fast non destructive sampling of the marker on surfaces of PFCs.
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| 57229. |
- Bykov, I., et al.
(author)
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Modification of adhered dust on plasma-facing surfaces due to exposure to ELMy H-mode plasma in DIII-D
- 2017
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In: NUCLEAR MATERIALS AND ENERGY. - : Elsevier BV. - 2352-1791. ; 12, s. 379-385
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Journal article (peer-reviewed)abstract
- Transient heat load tests have been conducted in the lower divertor of DIII-D using DiMES manipulator in order to study the behavior of dust on tungsten Plasma Facing Components (PFCs) during ELMy H-mode discharges. Samples with pre- adhered, pre- characterized dust have been exposed at the outer strike point (OSP) in a series of discharges with varied intra-(inter-) ELM heat fluxes. We used C dust because of its high sublimation temperature and non-metal properties. Al dust as a surrogate for Be and W dust were employed as relevant to that in the ITER divertor. The poor initial thermal contact between the substrate and the particles led to overheating, sublimation and shrinking of the carbon dust, and wetting induced coagulation of Al dust. Little modification of the W dust was observed. An enhanced surface adhesion and improvement of the thermal contact of C and Al dust were the result of exposure. A post mortem "adhesive tape" sampling showed that 70% of Al, <5% of W and C particles could not be removed from the surface owing to the improved adhesion. Al and C but not W particles that could be lifted had W inclusions indicating damage to the substrate. This suggests that non destructive methods may be inefficient for removal of dust in ITER.
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| 57230. |
- Bylund, Tomas
(author)
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Seeking the faint extremes : Detection and characterisation of extragalactic soft-spectrum gamma-ray sources and exploring methods to enhance their detection with machine learning in the 50 GeV-50 TeV energy range
- 2022
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Doctoral thesis (other academic/artistic)abstract
- This thesis deals with an observational study of Blazars, strong gamma-ray sources with Very High Energies (VHE) located far outside our Galaxy. Blazars are a class of galaxies that contain a supermassive black hole that is actively consuming large quantities of matter, a process that results in the liberation of tremendous amounts of energy that then powers the emission of huge bulks of charged particles that get accelerated almost to the speed of light.The details of the extreme processes involved are still very uncertain, and more observational studies are still required to discriminate between the various theories. Because it takes a lot of energy to create VHE gamma-rays, they are tightly coupled to the most energy-rich places in Blazars.This means that observations of gamma rays directly probe the central engine responsible for the enormous amounts of radiation we detect.Direct studies have been carried out with the H.E.S.S. observatory, an Imaging Atmospheric Cherenkov Telescope which uses our atmosphere as an integral part of its detector and is able to detect gamma-ray photons with energies from over 50 GeV up to tens of TeV.Using H.E.S.S., seven new sources of gamma-rays in the VHE regime were carefully studied in this thesis, significantly expanding the collection of known sources of TeV photons.Computer studies were also performed exploring the possibility of using deep learning to improve the sensitivity of ALTO, a newly-proposed observatory belonging to an emerging class of gamma-ray instruments, the particle detector arrays.
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