umu.sePublikationer
Ändra sökning
Avgränsa sökresultatet
12 1 - 50 av 76
RefereraExporteraLänk till träfflistan
Permanent länk
Referera
Referensformat
  • apa
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Annat format
Fler format
Språk
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Annat språk
Fler språk
Utmatningsformat
  • html
  • text
  • asciidoc
  • rtf
Träffar per sida
  • 5
  • 10
  • 20
  • 50
  • 100
  • 250
Sortering
  • Standard (Relevans)
  • Författare A-Ö
  • Författare Ö-A
  • Titel A-Ö
  • Titel Ö-A
  • Publikationstyp A-Ö
  • Publikationstyp Ö-A
  • Äldst först
  • Nyast först
  • Skapad (Äldst först)
  • Skapad (Nyast först)
  • Senast uppdaterad (Äldst först)
  • Senast uppdaterad (Nyast först)
  • Disputationsdatum (tidigaste först)
  • Disputationsdatum (senaste först)
  • Standard (Relevans)
  • Författare A-Ö
  • Författare Ö-A
  • Titel A-Ö
  • Titel Ö-A
  • Publikationstyp A-Ö
  • Publikationstyp Ö-A
  • Äldst först
  • Nyast först
  • Skapad (Äldst först)
  • Skapad (Nyast först)
  • Senast uppdaterad (Äldst först)
  • Senast uppdaterad (Nyast först)
  • Disputationsdatum (tidigaste först)
  • Disputationsdatum (senaste först)
Markera
Maxantalet träffar du kan exportera från sökgränssnittet är 250. Vid större uttag använd dig av utsökningar.
  • 1. Abdelsalam, UM
    et al.
    Moslem, WM
    Shukla, Padma Kant
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik. Institut für Theoretische Physik IV, Fakultät für Physik und Astronomie, Ruhr-Universität Bochum, D-44780 Bochum, Germany; Nonlinear Physics Centre & Center for Plasma Science and Astrophysics, Ruhr-Universität Bochum, D-44780 Bochum, Germany; Max-Planck-Institut für Extraterrestrische Physik, D-85741 Garching, Germany; GoLP/Instituto Superior Técnico, 1049-001 Lisbon, Portugal; CCLRC Centre for Fundamental Physics, Rutherford Appleton Laboratory, Chilton, Didcot, Oxon 0X11 0QX, UK; SUPA Department of Physics, University of Strathclyde, Glasgow G 40NG, UK; School of Physics, Faculty of Science & Agriculture, University of Kwazulu-Natal, Durban 4000, South Africa; Department of Physics, CITT, Islamabad, Pakistan.
    Localized electrostatic excitations in a Thomas-Fermi plasma containing degenerate electrons2008Ingår i: Physics of Plasmas, ISSN 1070-664X, E-ISSN 1089-7674, Vol. 15, nr 5, artikel-id 052303Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    By using the Thomas-Fermi electron density distribution for quantum degenerate electrons, the hydrodynamic equations for ions, and the Poisson equation, planar and nonplanar ion-acoustic solitary waves in an unmagnetized collisionless plasma are investigated. The reductive perturbation method is used to derive cylindrical and spherical Korteweg-de Vries equations. Numerical solutions of the latter are presented. The present results can be useful in understanding the features of small but finite amplitude localized ion-acoustic solitary pulses in a degenerate plasma.

  • 2. Adhikary, N C
    et al.
    Misra, Amar P
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Bailung, H
    Chutia, J
    Ion-beam driven dust ion-acoustic solitary waves in dusty plasmas2010Ingår i: Physics of Plasmas, ISSN 1070-664X, E-ISSN 1089-7674, Vol. 17, nr 4, artikel-id 044502Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The nonlinear propagation of small but finite amplitude dust ion-acoustic waves (DIAWs) in an ion-beam driven plasma consisting of Boltzmannian electrons, positive ions, and stationary negatively charged dust grains is studied by using the standard reductive perturbation technique. It is shown that there exist two critical values (γc1) and (γc2) of ion beam to ion phase velocity ratio (γ), above and below which the beam generated solitons are not possible. The effects of the parameters, namely, γ, the ratio of the ion beam to plasma ion density (μi), the dust to ion density ratio (μd), and the ion beam to plasma ion mass ratio (μ) on both the amplitude and width of the stationary DIAWs, are analyzed numerically, and applications of the results to laboratory ion beam as well as space plasmas (e.g., auroral plasmas) are explained.

  • 3. Ali, S
    et al.
    Moslem, W.M.
    Shukla, P.K.
    Umeå universitet, Teknisk-naturvetenskaplig fakultet, Fysik.
    Schlickeiser, R.
    Linear and nonlinear ion-acoustic waves in an unmagnetized electron-positron-ion quantum plasma2007Ingår i: Physics of Plasmas, ISSN 1070-664X, E-ISSN 1089-7674, Vol. 14, s. 82307-Artikel i tidskrift (Refereegranskat)
  • 4. Ali, S
    et al.
    Shukla, Padma K
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik. Institut für Theoretische Physik IV, Fakultät für Physik und Astronomie, Ruhr-Universität Bochum, D-44780 Bochum, Germany; Max-Planck Institut für extraterrestrische Physik, D-85741 Garching, Germany, GoLP/Instituto Superior Técnico, 1049-001 Lisbon, Portugal, Centre for Fundamental Physics, Rutherford Appleton Laboratory, Chilton, Didcot, Oxon 0X11 0QX, United Kingdom, and Department of Physics, University of Strathclyde, Glasgow, Scotland, United Kingdom .
    Dust acoustic solitary waves in a quantum plasma2006Ingår i: Physics of Plasmas, ISSN 1070-664X, E-ISSN 1089-7674, Vol. 13, nr 2, artikel-id 022313Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    By employing one-dimensional quantum hydrodynamic (QHD) model for a three species quantum plasma, nonlinear properties of dust acoustic solitary waves are studied. For this purpose a Korteweg-de Vries (KdV) equation is derived, incorporating quantum corrections. The quantum mechanical effects are also examined numerically both on the profiles of the amplitude and the width of dust acoustic solitary waves. It is found that the amplitude remains constant but the width shrinks for different values of a dimensionless electron quantum parameter H-e=root(Z(d0)h(2)omega(2)(pd))/m(e)m(d)C(d)(4), where Z(d0) is the dust charge state, h is the Planck constant divided by 2 pi, omega(pd) is the dust plasma frequency, m(e) (m(d)) is the electron (dust) mass, and C-d is the dust acoustic speed.

  • 5. Ali, S
    et al.
    Shukla, Padma Kant
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik. Institut für Theoretische Physik IV and Centre for Plasma Science and Astrophysics, Fakultät für Physik und Astronomie, Ruhr-Universität Bochum, D-44780 Bochum, Germany; Max-Planck Institut für extraterrestrische Physik, D-85741 Garching, Germany; GoLP/Instituto Superior Técnico, 1049-001 Lisbon, Portugal; Centre for Fundamental Physics, Rutherford Appleton Laboratory, Chilton, Didcot, Oxon 0X11 0QX, United Kingdom; Department of Physics, University of Strathclyde, Glasgow, Scotland, United Kingdom.
    Dispersion properties of compressional electromagnetic waves in quantum dusty magnetoplasmas2006Ingår i: Physics of Plasmas, ISSN 1070-664X, E-ISSN 1089-7674, Vol. 13, nr 5, artikel-id 052113Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A new dispersion relation for low-frequency compressional electromagnetic waves is derived by employing quantum magnetohydrodynamic model and Maxwell equations in cold quantum dusty magnetoplasmas. The latter is composed of inertialess electrons, mobile ions, and immobile charged dust particulates. The dispersion relation for the low-frequency compressional electromagnetic modes is further analyzed for the waves propagating parallel, perpendicular, and oblique to the external magnetic field direction. It is found theoretically and numerically that the quantum parameter alpha(q)=(n(i0)/n(e0))h(2)/(4m(e)m(i)) affects the real angular frequencies and the phase speeds of the compressional electromagnetic modes. Here, n(i0) (n(e0)) is the equilibrium number density of the ions (electrons), m(e) (m(i)) is the electron (ion) mass, and h is the Plank constant divided by 2 pi.

  • 6. Badziak, J
    et al.
    Mishra, G
    Gupta, N K
    Holkundkar, Amol
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Generation of ultraintense proton beams by multi-ps circularly polarized laser pulses for fast ignition-related applications2011Ingår i: Physics of Plasmas, ISSN 1070-664X, E-ISSN 1089-7674, Vol. 18, nr 5, artikel-id 053108Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A scheme of generation of ultraintense proton beams relevant for proton fast ignition (PFI) which employs multi-ps, circularly polarized laser pulse irradiating a thick (≥ 10 μm) H-rich target is proposed and examined using one-dimensional particle-in cell-simulations. It is shown that a 5-ps laser pulse of intensity ∼ (2–5) × 1020W/cm2 irradiating the target of the areal proton density ∼ 2 × 1020cm−2 can produce – with a high energetic efficiency – a proton beam (plasma block) of parameters (intensity, energy fluence, pulse duration, proton energy spectrum) close to those required for PFI. At a fixed total laser energy, the proton beam parameters can be controlled and fitted to the PFI requirements by changing the laser intensity (energy fluence) and/or the target thickness as well as by using a shaped (curved) target inserted into a guiding cone.

  • 7. Bains, AS
    et al.
    Misra, Amar P
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Saini, NS
    Gill, TS
    Modulational instability of ion-acoustic wave envelopes in magnetized quantum electron-positron-ion plasmas2010Ingår i: Physics of Plasmas, ISSN 1070-664X, E-ISSN 1089-7674, Vol. 17, nr 1, artikel-id 012103Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The amplitude modulation of quantum ion-acoustic waves (QIAWs) along an external magnetic field is studied in a quantum electron-positron-ion (e-p-i) magnetoplasma. Reductive perturbation technique is used to derive the three-dimensional nonlinear Schroumldinger equation which governs the slow modulation of QIAW packets. Accounting for the effects of the electron to ion number density ratio (mu), the normalized ion-cyclotron frequency (omega(c)) as well as the ratio (H) of the "plasmonic energy density" to the Fermi energy, new regimes for the modulational instability of QIAWs are obtained and analyzed. In contrast to one-dimensional unmagnetized e-p-i plasmas, the instability growth rate is shown to suppress with increasing mu or decreasing the values of H. The predicted results could be important for understanding the salient features of modulated QIAW packets in dense astrophysical plasmas as well as to the next generation intense laser solid density plasma experiments.

  • 8.
    Bergman, Jan
    et al.
    Swedish Institute of Space Physics, Box 537, SE-751 21 Uppsala, Sweden.
    Eliasson, Bengt
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Erratum:: "Linear wave dispersion laws in unmagnetized relativistic plasma: Analytical and numerical results" [Phys. Plasmas 8, 1482 (2001)]2009Ingår i: Physics of Plasmas, ISSN 1070-664X, E-ISSN 1089-7674, Vol. 16, nr 12, s. 129902-Artikel i tidskrift (Refereegranskat)
  • 9. Bhowmik, C.
    et al.
    Bhowmik, A. P.
    Shukla, P.K.
    Umeå universitet, Teknisk-naturvetenskaplig fakultet, Fysik.
    Oblique modulation of electron-acoustic waves in a Fermi electron-ion plasma2007Ingår i: Physics of Plasmas, ISSN 1070-664X, E-ISSN 1089-7674, Vol. 14, s. 122107-Artikel i tidskrift (Refereegranskat)
  • 10.
    Brodin, Gert
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Marklund, Mattias
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Spin solitons in magnetized pair plasmas2007Ingår i: Physics of Plasmas, ISSN 1070-664X, E-ISSN 1089-7674, Vol. 14, nr 11, s. 2107-4 sidorArtikel i tidskrift (Refereegranskat)
    Abstract [en]

    A set of fluid equations, taking into account the spin properties of the electrons and positrons in a magnetoplasma, are derived. The magnetohydrodynamic limit of the pair plasma is investigated. It is shown that the microscopic spin properties of the electrons and positrons can lead to interesting macroscopic and collective effects in strongly magnetized plasmas. In particular, it is found that new Alfvénic solitary structures, governed by a modified Korteweg–de Vries equation, are allowed in such plasmas. These solitary structures vanish if the quantum spin effects are neglected. Our results should be of relevance for astrophysical plasmas, e.g., in pulsar magnetospheres, as well as for low-temperature laboratory plasmas.

  • 11.
    Brodin, Gert
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Stenflo, L.
    Nonlinear dynamics of a cold collisional electron plasma2017Ingår i: Physics of Plasmas, ISSN 1070-664X, E-ISSN 1089-7674, Vol. 24, nr 12, artikel-id 124505Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We study the influence of collisions on the dynamics of a cold non-relativistic plasma. It is shown that even a comparatively small collision frequency can significantly change the large amplitude wave solution.

  • 12.
    Brodin, Gert
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Stenflo, L.
    Nonlinear dynamics of large amplitude modes in a magnetized plasma2014Ingår i: Physics of Plasmas, ISSN 1070-664X, E-ISSN 1089-7674, Vol. 21, nr 12, artikel-id 122301Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We derive two equations describing the coupling between electromagnetic and electrostatic oscillations in one-dimensional geometry in a magnetized cold and non-relativistic plasma. The nonlinear interaction between the wave modes is studied numerically. The effects of the external magnetic field strength and the initial electromagnetic polarization are of particular interest here. New results can, thus, be identified. 

  • 13.
    Brodin, Gert
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Stenflo, L.
    Three-wave coupling coefficients for perpendicular wave propagation in a magnetized plasma2015Ingår i: Physics of Plasmas, ISSN 1070-664X, E-ISSN 1089-7674, Vol. 22, nr 10, artikel-id 104503Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The resonant interaction between three waves in a uniform magnetized plasma is reconsidered. Starting from previous kinetic expressions, we limit our investigation to waves propagating perpendicularly to the external magnetic field. It is shown that reliable results can only be obtained in the two-dimensional case, i.e., when the wave vectors have both x and y components. 

  • 14.
    Bychkov, Vitaly
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Modestov, Mikhail
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Marklund, Mattias
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Magnetohydrodynamic instability in plasmas with intrinsic magnetization2010Ingår i: Physics of Plasmas, ISSN 1070-664X, E-ISSN 1089-7674, Vol. 17, nr 11, s. 112107-112112Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    From a magnetofluid description with intrinsic magnetization, a new plasma instability is obtained. The plasma magnetization is produced by the collective electron spin. The instability develops in a nonuniform plasma when the electron concentration and temperature vary along an externally applied magnetic field. Alfvén waves play an important role in the instability. The instability properties are numerically investigated for a particular example of an ultrarelativistic degenerate plasma in exploding white dwarfs.

  • 15.
    Bychkov, Vitaly
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Modestov, Mikhail
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Marklund, Mattias
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    The Darrieus-Landau instability in fast deflagration and laser ablation2008Ingår i: Physics of Plasmas, ISSN 1070-664X, E-ISSN 1089-7674, Vol. 15, nr 3, s. 032702-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The problem of the Darrieus-Landau instability at a discontinuous deflagration front in a compressible flow is solved. Numerous previous attempts to solve this problem suffered from the deficit of boundary conditions. Here, the required additional boundary condition is derived rigorously taking into account the internal structure of the front. The derived condition implies a constant mass flux at the front; it reduces to the classical Darrieus-Landau condition in the limit of an incompressible flow. It is demonstrated that in general the solution to the problem depends on the type of energy source in the flow. In the common case of a strongly localized source, compression effects make the Darrieus-Landau instability considerably weaker. Particularly, the instability growth rate is reduced for laser ablation in comparison to the classical incompressible case. The instability disappears completely in the Chapman-Jouguet regime of ultimately fast deflagration.

  • 16.
    Bychkov, Vitaly
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Modestov, Mikhail
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Marklund, Mattias
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    The structure of weak shocks in quantum plasmas2008Ingår i: Physics of Plasmas, ISSN 1070-664X, E-ISSN 1089-7674, Vol. 15, nr 3, s. 032309-032322Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The structure of a weak shock in a quantum plasma is studied, taking into account both dissipation terms due to thermal conduction and dispersive quantum terms due to the Bohm potential. Unlike quantum systems without dissipations, even a small thermal conduction may lead to a stationary shock structure. In the limit of zero quantum effects, the monotonic Burgers solution for the weak shock is recovered. Still, even small quantum terms make the structure nonmonotonic with the shock driving a train of oscillations into the initial plasma. The oscillations propagate together with the shock. The oscillations become stronger as the role of Bohm potential increases in comparison with thermal conduction. The results could be of importance for laser-plasma interactions, such as inertial confinement fusion plasmas, and in astrophysical environments, as well as in condensed matter systems.

  • 17. Daldorff, LKS
    et al.
    Pecseli, HL
    Trulsen, JK
    Ulriksen, MI
    Eliasson, Bengt
    Stenflo, Lennart
    Department of Physics, Linköping University, SE-58183 Linköping, Sweden .
    Nonlinear beam generated plasma waves as a source for enhanced plasma and ion acoustic lines2011Ingår i: Physics of Plasmas, ISSN 1070-664X, E-ISSN 1089-7674, Vol. 18, nr 15, s. 052107-052114Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Observations by, for instance, the EISCAT Svalbard Radar (ESR) demonstrate that the symmetry of the naturally occurring ion line in the polar ionosphere can be broken by an enhanced, nonthermal, level of fluctuations (naturally enhanced ion-acoustic lines, NEIALs). It was in many cases found that the entire ion spectrum can be distorted, also with the appearance of a third line, corresponding to a propagation velocity significantly slower than the ion acoustic sound speed. It has been argued that selective decay of beam excited primary Langmuir waves can explain some phenomena similar to those observed. We consider a related model, suggesting that a primary nonlinear process can be an oscillating two-stream instability, generating a forced low frequency mode that does not obey any ion sound dispersion relation. At later times, the decay of Langmuir waves can give rise also to enhanced asymmetric ion lines. The analysis is based on numerical results, where the initial Langmuir waves are excited by a cold dilute electron beam. By this numerical approach, we can detect fine details of the physical processes, in particular, demonstrate a strong space-time intermittency of the electron waves in agreement with observations. Our code solves the full Vlasov equation for electrons and ions, with the dynamics coupled through the electrostatic field derived from Poisson's equation. The analysis distinguishes the dynamics of the background and beam electrons. This distinction simplifies the analysis for the formulation of the weakly nonlinear analytical model for the oscillating two-stream instability. The results have general applications beyond their relevance for the ionospheric observations.

  • 18.
    Eliasson, Bengt
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Shukla, Padma Kant
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Pavlenko, V.P.
    Department of Physics and Astronomy, Uppsala University, SE-751 20 Uppsala, Sweden.
    Dynamics of nonlinearly interacting magnetic electron drift vortex modes in a nonuniform plasma2009Ingår i: Physics of Plasmas, ISSN 1070-664X, E-ISSN 1089-7674, Vol. 16, s. 042306-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Asimulation study of dynamical evolution of nonlinearly interacting two-dimensional magneticelectron drift vortex (MEDV) modes in a nonuniform plasma ispresented. Depending on the equilibrium density and temperature gradients, thesystem can either be stable or unstable. The unstable systemreveals spontaneous generation of magnetic fields from noise level, andlarge-scale magnetic field structures are formed. When the system islinearly stable, one encounters MEDV mode turbulence in which thereis a competition between zonons (zonal flows) and streamers. Forlarge MEDV mode amplitudes, one encounters the formation of localizedand small-scale magnetic vortices and vortex pairs with scale sizesof the order of the electron skin depth. The MEDVturbulence exhibits nonuniversal (non-Kolmogorov-type) spectra for different sets of plasmaparameters. The relevance of this work to laboratory and cosmicplasmas is briefly mentioned.

  • 19. El-Shamy, E. F.
    et al.
    Sabry, R.
    Moslem, W. M.
    Shukla, P. K.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik. Ruhr Univ Bochum, Inst Theoret Phys 4, Fak Phys & Astron, D-44780 Bochum, Germany; Ruhr Univ Bochum, Nonlinear Phys Ctr, D-44780 Bochum, Germany; Ruhr Univ Bochum, Ctr Plasma Sci & Astrophys, D-44780 Bochum, Germany; Rutherford Appleton Lab, Ctr Fundamental Phys, CCLRC, Didcot 0X11 OQX, Oxon, England; Univ Strathclyde, SUPA Dept Phys, Glasgow G 40NG, Lanark, Scotland; Univ Kwazulu Natal, Sch Phys, Fac Sci & Agr, ZA-4000 Durban, South Africa.
    Head-on collision of ion-acoustic solitary waves in multicomponent plasmas with positrons2010Ingår i: Physics of Plasmas, ISSN 1070-664X, E-ISSN 1089-7674, Vol. 17, nr 8, artikel-id 082311Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The head-on collision between two ion-acoustic solitary waves in an unmagnetized multicomponent plasma consisting of hot ions, hot positrons, and two-electron temperature distributions is investigated using the extended Poincare-Lighthill-Kuo method. The Kortwege-de Vries equations and the analytical phase shifts after the head-on collision of two solitary waves in this multicomponent plasma are obtained. The effects of two different types of isothermal electrons, the ratio of the hot ion temperature to the effective temperature, the ratio of the effective temperature to the positron temperature, the ratio of the number density of positrons to that of electrons species, and the physical processes (either isothermal or adiabatic) on the phase shifts are studied. It is found that these parameters can significantly influence the phase shifts of the solitons. The relevance of this investigation to space and laboratory plasmas is pointed out. 

  • 20. Gunell, H.
    et al.
    De Keyser, J.
    Mann, Ingrid
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik. EISCAT Scientific Association, Kiruna.
    Numerical and laboratory simulations of auroral acceleration2013Ingår i: Physics of Plasmas, ISSN 1070-664X, E-ISSN 1089-7674, Vol. 20, nr 10, s. Article number: 102901-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The existence of parallel electric fields is an essential ingredient of auroral physics, leading to the acceleration of particles that give rise to the auroral displays. An auroral flux tube is modelled using electrostatic Vlasov simulations, and the results are compared to simulations of a proposed laboratory device that is meant for studies of the plasma physical processes that occur on auroral field lines. The hot magnetospheric plasma is represented by a gas discharge plasma source in the laboratory device, and the cold plasma mimicking the ionospheric plasma is generated by a Q-machine source. In both systems, double layers form with plasma density gradients concentrated on their high potential sides. The systems differ regarding the properties of ion acoustic waves that are heavily damped in the magnetosphere, where the ion population is hot, but weakly damped in the laboratory, where the discharge ions are cold. Ion waves are excited by the ion beam that is created by acceleration in the double layer in both systems. The efficiency of this beam-plasma interaction depends on the acceleration voltage. For voltages where the interaction is less efficient, the laboratory experiment is more space-like. (C) 2013 AIP Publishing LLC.

  • 21. Gunell, H.
    et al.
    Nilsson, H.
    Stenberg, G.
    Hamrin, Maria
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Karlsson, T.
    Maggiolo, R.
    Andre, M.
    Lundin, R.
    Dandouras, I.
    Plasma penetration of the dayside magnetopause2012Ingår i: Physics of Plasmas, ISSN 1070-664X, E-ISSN 1089-7674, Vol. 19, nr 7, s. 072906-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Data from the Cluster spacecraft during their magnetopause crossing on 25 January 2002 are presented. The magnetopause was in a state of slow non-oscillatory motion during the observational period. Coherent structures of magnetosheath plasma, here typified as plasmoids, were seen on closed magnetic field lines on the inside of the magnetopause. Using simultaneous measurements on two spacecraft, the inward motion of the plasmoids is followed from one spacecraft to the next, and it is found to be in agreement with the measured ion velocity. The plasma characteristics and the direction of motion of the plasmoids show that they have penetrated the magnetopause, and the observations are consistent with the concept of impulsive penetration, as it is known from theory, simulations, and laboratory experiments. The mean flux across the magnetopause observed was 0.2%-0.5% of the solar wind flux at the time, and the peak values of the flux inside the plasmoids reached approximately 20% of the solar wind flux. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4739446]

  • 22. Haas, F
    et al.
    Shukla, Padma Kant
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik. Institut für Theoretische Physik IV, Ruhr-Universität Bochum, D-44780 Bochum, Germany; GOLP/Instituto de Plasmas e Fusão Nuclear, Instituto Superior Técnico, Universidade Técnica de Lisboa, 1049-001 Lisboa, Portugal; SUPA, Department of Physics, University of Strathclyde, Glasgow, G40NG, UK; School of Physics, University of Kwazulu-Natal, Durban 4000, South Africa.
    Nonlinear stationary solutions of the Wigner and Wigner-Poisson equations2008Ingår i: Physics of Plasmas, ISSN 1070-664X, E-ISSN 1089-7674, Vol. 15, nr 11, artikel-id 112302Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Exact nonlinear stationary solutions of the one-dimensional Wigner and Wigner-Poisson equations in the terms of the Wigner functions that depend not only on the energy but also on position are presented. In this way, the Bernstein-Greene-Kruskal modes of the classical plasma are adapted for the quantum formalism in the phase space. The solutions are constructed for the case of a quartic oscillator potential, as well as for the self-consistent Wigner-Poisson case. Conditions for well-behaved physically meaningful equilibrium Wigner functions are discussed.

  • 23. Haas, F
    et al.
    Shukla, Padma Kant
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik. Institut für Theoretische Physik IV, Ruhr-Universität Bochum, D-44780 Bochum, Germany; GOLP/Instituto de Plasmas e Fusão Nuclear, Instituto Superior Técnico, Universidade Técnica de Lisboa, 1049-001 Lisboa, Portugal; SUPA, Department of Physics, University of Strathclyde, Glasgow, G40NG, United Kingdom; School of Physics, University of Kwazulu-Natal, Durban 4000, South Africa.
    Nonlinear structure in a current-carrying collisional dusty plasma2008Ingår i: Physics of Plasmas, ISSN 1070-664X, E-ISSN 1089-7674, Vol. 15, nr 9, artikel-id 093702Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A perpendicular ion drift is proposed as a possible mechanism for the generation of magnetic field structures in a highly collisional dusty plasma. The basic dissipation mechanism is assumed to be the dust-neutral momentum exchange, so that plasmas with a small ionization fraction are natural candidates for experiments. The model reduces to a nonlinear partial differential equation for the vector potential. The conditions for linear instability are presented. Possible stationary states are periodic arrangements for the magnetic field, described by a Lienard equation. The fully depleted (ion-dust) case is also considered in detail. Applications of the present work to magnetic field structures in planetary rings, comets, and low-temperature dusty plasma experiments are discussed. A necessary condition for the validity of the model is a sufficiently slow time scale of the generated magnetic fields in dusty plasmas.

  • 24.
    Holkundkar, Amol
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Mishra, Gaurav
    Gupta, N K
    Molecular dynamic simulation for laser–cluster interaction2011Ingår i: Physics of Plasmas, ISSN 1070-664X, E-ISSN 1089-7674, Vol. 18, nr 5, artikel-id 053102Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A three dimensional relativistic molecular dynamic model for studying the laser interaction with atomic clusters is presented. The model is used to simulate the interaction dynamics of deuterium, argon, and xenon clusters when irradiated by the short and high intensity laser pulses. The interaction of 82 Å argon cluster by 100 fs, 806 nm laser pulse with the peak intensity of 8 × 1015 W/cm2 is studied and compared with the experimental results. The maximum ion energy in this case is found to be about 200 keV. Ion energies along and perpendicular to laser polarization direction is calculated and asymmetry along laser polarization direction is detected which is further explained on the basis of charge flipping model. The effect of cluster density on the energetics of the laser–cluster interaction is also being studied, which provides a qualitative understanding of the presence of optimum cluster size for maximum ion energies.

  • 25.
    Hussain, Azhar
    et al.
    Department of Physics, GC University Lahore, 54000 Lahore, Pakistan.
    Stefan, Martin
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Brodin, Gert
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Weakly relativistic quantum kinetic theory for electrostatic wave modes in magnetized plasmas2014Ingår i: Physics of Plasmas, ISSN 1070-664X, E-ISSN 1089-7674, Vol. 21, nr 3, s. 032104-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We have derived the electrostatic dispersion relation in a magnetized plasma using a recently developed quantum kinetic model based on the Dirac equation. The model contains weakly relativistic spin effects such as Thomas precession, the polarization currents associated with the spin and the spin-orbit coupling. It turns out that for strictly electrostatic perturbations the non-relativistic spin effects vanish, and the modification of the classical dispersion relation is solely associated with the relativistic terms. Several new wave modes appear due the electron spin effects, and an example for astrophysical plasmas are given. (C) 2014 AIP Publishing LLC.

  • 26.
    Jenab, S. M. Hosseini
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Brodin, Gert
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Head-on collision of nonlinear solitary solutions to Vlasov-Poisson equations2019Ingår i: Physics of Plasmas, ISSN 1070-664X, E-ISSN 1089-7674, Vol. 26, nr 2, artikel-id 022303Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Nonlinear solitary solutions to the Vlasov-Poisson set of equations are studied in order to investigate their stability by employing a fully kinetic simulation approach. This study is carried out in the ion-acoustic regime for a collisionless, electrostatic, and Maxwellian electron-ion plasma. The trapped population of electrons is modeled based on the well-known Schamel distribution function. Head-on mutual collisions of nonlinear solutions are performed in order to examine their collisional stability. The findings include three major aspects: (I) These nonlinear solutions are found to be divided into three categories based on their Mach numbers, i.e., stable, semi-stable, and unstable. Semi-stable solutions indicate a smooth transition from stable to unstable solutions for the increasing Mach number. (II) The stability of solutions is traced back to a condition imposed on averaged velocities, i.e., net neutrality. It is shown that a bipolar structure is produced in the flux of electrons, early in the temporal evolution. This bipolar structure acts as the seed of the net-neutrality instability, which tips off the energy balance of nonlinear solution during collisions. As the Mach number increases, the amplitude of the bipolar structure grows and results in a stronger instability. (III) It is established that during mutual collisions, a merging process of electron holes can occur to a variety of degrees, based on their velocity characteristics. Specifically, the number of rotations of electron holes around each other (in the merging phase) varies. Furthermore, it is observed that in the case of a non-integer number of rotations, two electron holes exchange their phase space cores.

  • 27.
    Jenab, S. M. Hosseini
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik. Centre for Space Research, North-West University, Potchefstroom Campus, Potchefstroom, South Africa.
    Spanier, F.
    Brodin, Gert
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik. Centre for Space Research, North-West University, Potchefstroom Campus, Potchefstroom, South Africa.
    Scattering of electron holes in the context of ion-acoustic regime2019Ingår i: Physics of Plasmas, ISSN 1070-664X, E-ISSN 1089-7674, Vol. 26, nr 3, artikel-id 034502Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Mutual collisions between ion-acoustic solitary waves are studied based on a fully kinetic simulation approach. Two cases, small and large relative velocities, are studied, and the effect of trapped electron population on the collision process is focused upon. It is shown that, for the case of small relative velocity, the repelling force between the trapped populations of electrons results in scattering of electron holes. However, this phenomenon cannot be witnessed if the relative velocity is considerably high since the impact of trapped population remains very weak.

  • 28.
    Jenab, Seyyed Mehdi Hosseini
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Spanier, F.
    Brodin, Gert
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    A study of the stability properties of Sagdeev solutions in the ion-acoustic regime using kinetic simulations2018Ingår i: Physics of Plasmas, ISSN 1070-664X, E-ISSN 1089-7674, Vol. 25, nr 7, artikel-id 072304Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The Sagdeev pseudo-potential approach has been employed extensively in theoretical studies to determine large-amplitude (fully) nonlinear solutions in a variety of multi-species plasmas. Although these solutions are repeatedly considered as solitary waves (and even solitons), their temporal stability has never been proven. In this paper, a numerical study of the Vlasov-Poisson system is made to follow their temporal evolution in the presence of numerical noise and thereby test their long-time propagation stability. Considering the ion-acoustic regime, both constituents of the plasma, i.e., electrons and ions are treated following their distribution functions in these sets of fully-kinetic simulations. The findings reveal that the stability of the Sagdeev solution depends on a combination of two parameters, i.e., velocity and trapping parameter. It is shown that there exists a critical value of trapping parameter for both fast and slow solutions which separates stable from unstable solutions. In the case of stable solutions, it is shown that these nonlinear structures can propagate for long periods, which confirms their status as solitary waves. Stable solutions are reported for both Maxwellian and Kappa distribution functions. For unstable solutions, it is demonstrated that the instability causes the Sagdeev solution to decay by emitting ion-acoustic wave-packets on its propagation trail. The instability is shown to take place in a large range of velocities and even for Sagdeev solutions with a velocity much higher than the ion-sound speed. Besides, in order to validate our simulation code, two precautionary measures are taken. First, the well-known effect of the ion dynamics on a stationary electron hole solution is presented as a benchmarking test of the approach. Second, In order to verify the numerical accuracy of the simulations, the conservation of energy and entropy is presented.

  • 29.
    Karimov, A. R.
    et al.
    Institute for High Temperatures, Russian Academy of Sciences, Izhorskaya 13/19, Moscow 127412, Russia.
    Stenflo, Lennart
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Yu, M. Y.
    Department of Physics, Institute for Fusion Theory and Simulation, Zhejiang University, 310027 Hangzhou, China.
    Coupled azimuthal and radial flows and oscillations in a rotating plasma2009Ingår i: Physics of Plasmas, ISSN 1070-664X, E-ISSN 1089-7674, Vol. 16, s. 062313-062319Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    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.

  • 30. Karimov, A. R.
    et al.
    Stenflo, Lennart
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Yu, M. Y.
    Coupled flows and oscillations in asymmetric rotating plasmas2009Ingår i: Physics of Plasmas, ISSN 1070-664X, E-ISSN 1089-7674, Vol. 16, nr 10, s. 102303-102307Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    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.

  • 31. Karimov, A. R.
    et al.
    Yu, M. Y.
    Stenflo, Lennart
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik. Department of Physics, Linköping University, SE-58183 Linköping, Sweden.
    Expansion of a cold non-neutral plasma slab2014Ingår i: Physics of Plasmas, ISSN 1070-664X, E-ISSN 1089-7674, Vol. 21, nr 12, artikel-id 122304Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    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. 

  • 32.
    Lundin, Joakim
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Brodin, Gert
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Marklund, Mattias
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Short wavelength quantum electrodynamical correction to cold plasma-wave propagation2006Ingår i: Physics of Plasmas, ISSN 1070-664X, E-ISSN 1089-7674, Vol. 13, nr 10, s. 102102-102107Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The effect of short wavelength quantum electrodynamic (QED) correction on plasma-wave propagation is investigated. The effect on plasma oscillations and on electromagnetic waves in an unmagnetized as well as a magnetized plasma is investigated. The effects of the short wavelength QED corrections are most evident for plasma oscillations and for extraordinary modes. In particular, the QED correction allow plasma oscillations to propagate, and the extraordinary mode loses its stop band. The significance of our results is discussed.

  • 33.
    Lundin, Joakim
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Marklund, Mattias
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Brodin, Gert
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Modified Jeans instability criteria for magnetized systems2008Ingår i: Physics of Plasmas, ISSN 1070-664X, E-ISSN 1089-7674, Vol. 15, nr 7, s. 072116-072121Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The Jeans instability is analyzed for dense magnetohydrodynamic plasmas with intrinsic magnetization, the latter due to collective electron spin effects. Furthermore, the effects of electron tunneling as well as the Fermi pressure are included. It is found that the intrinsic magnetization of the plasma will enhance the Jeans instability, and can significantly modify the structure of the instability spectra. Implications and limitations of our results are discussed, as well as possible generalizations.

  • 34.
    Lundin, Joakim
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Stenflo, Lennart
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Brodin, Gert
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Marklund, Mattias
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Shukla, Padma K
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Circularly polarized waves in a plasma with vacuum polarization effects2007Ingår i: Physics of Plasmas, ISSN 1070-664X, E-ISSN 1089-7674, Vol. 14, nr 6, s. 064503-3 sidorArtikel i tidskrift (Refereegranskat)
    Abstract [en]

    The theory for large amplitude circularly polarized waves propagating along an external magnetic field is extended in order to also include vacuum polarization effects. A general dispersion relation, which unites previous results, is derived.

  • 35.
    Lundin, Joakim
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Zamanian, Jens
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Marklund, Mattias
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Brodin, Gert
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Short wavelength electromagnetic propagation in magnetized quantum plasmas2007Ingår i: Physics of Plasmas, ISSN 1070-664X, E-ISSN 1089-7674, Vol. 14, nr 6, s. 2112-7 sidorArtikel i tidskrift (Refereegranskat)
    Abstract [en]

    The quantum electrodynamical (QED) short wavelength correction on plasma wave propagation for a nonrelativistic quantum plasma is investigated. A general dispersion relation for a thermal multicomponent quantum plasma is derived. It is found that the classical dispersion relation for any wave mode can be modified to include quantum and short wavelength QED effects by simple substitutions of the thermal velocity and the plasma frequency. Furthermore, the dispersion relation has been modified to include QED effects of strong magnetic fields. It is found that strong magnetic fields together with the short wavelength QED correction will induce dispersion both in vacuum and in otherwise nondispersive plasma modes. Applications to laboratory and astrophysical systems are discussed.

  • 36. Ma, Guangjin
    et al.
    Dallari, William
    Borot, Antonin
    Krausz, Ferenc
    Yu, Wei
    Tsakiris, George D.
    Veisz, László
    Max-Planck-Institut für Quantenoptik, Garching, Germany.
    Intense isolated attosecond pulse generation from relativistic laser plasmas using few-cycle laser pulses2015Ingår i: Physics of Plasmas, ISSN 1070-664X, E-ISSN 1089-7674, Vol. 22, nr 3, artikel-id 033105Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We have performed a systematic study through particle-in-cell simulations to investigate the generation of attosecond pulse from relativistic laser plasmas when laser pulse duration approaches the few-cycle regime. A significant enhancement of attosecond pulse energy has been found to depend on laser pulse duration, carrier envelope phase, and plasma scale length. Based on the results obtained in this work, the potential of attaining isolated attosecond pulses with ∼100 μJ energy for photons >16 eV using state-of-the-art laser technology appears to be within reach.

  • 37.
    Mamun, A. A.
    et al.
    Institut für Theoretische Physik IV, Fakultät für Physik und Astronomie, Ruhr-Universität Bochum, Bochum D-44780, Germany.
    Shukla, Padma Kant
    Institut für Theoretische Physik IV, Fakultät für Physik und Astronomie, Ruhr-Universität Bochum, Bochum D-44780, Germany.
    Eliasson, Bengt
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Arbitrary amplitude dust ion-acoustic shock waves in a dusty plasma with positive and negative ions2009Ingår i: Physics of Plasmas, ISSN 1070-664X, E-ISSN 1089-7674, Vol. 16, s. 114503-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Arbitraryamplitude dust ion-acoustic shock waves in a multi-ion dusty plasma(composed of electrons, light positive ions, heavy negative ions, andstationary massive dust grains) has been studied. For this purpose,the coupled Poisson and dust-charging equations, which accounts for thefluctuation of charges on static dust, have been numerically solved.The large amplitude shocks are associated with a sudden decreasein the electrostatic potential and of the dust grain charge.It is found that in the lower speed limit smallamplitude shocks are formed, while in the larger speed limitlarge amplitude shocks are formed. It is anticipated that theprofiles and amplitudes of the DIA shocks predicted here willbe observed in forthcoming laboratory and space experiments.

  • 38.
    Marklund, Mattias
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik. Centre for Fundamental Physics, Rutherford Appleton Laboratory, Chilton Didcot, Oxfordshire OX11 0QX, United Kingdom .
    Stenflo, Lennart
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Shukla, Padma Kant
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik. Centre for Fundamental Physics, Rutherford Appleton Laboratory, Chilton Didcot, Oxfordshire OX11 0QX, United Kingdom .
    Brodin, Gert
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik. Centre for Fundamental Physics, Rutherford Appleton Laboratory, Chilton Didcot, Oxfordshire OX11 0QX, United Kingdom .
    Quantum electrodynamical effects in dusty plasmas2005Ingår i: Physics of Plasmas, ISSN 1070-664X, E-ISSN 1089-7674, Vol. 12, nr 7, artikel-id 072111Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A new nonlinear electromagnetic wave mode in a magnetized dusty plasma is predicted. Its existence depends on the interaction of an intense circularly polarized electromagnetic wave with a dusty plasma, where quantum electrodynamical photon-photon scattering is taken into account. Specifically, we consider a dusty electron-positron-ion plasma and show that the propagation of the new mode is admitted. It could be of significance for the physics of supernova remnants and in neutron star formation.

  • 39. Masood, W.
    et al.
    Eliasson, Bengt
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Electrostatic solitary waves in a quantum plasma with relativistically degenerate electrons2011Ingår i: Physics of Plasmas, ISSN 1070-664X, E-ISSN 1089-7674, Vol. 18, nr 3, artikel-id 034503Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A model for nonlinear ion waves in an unmagnetized plasma with relativistically degenerate electrons and cold fluid ions is presented here. The inertia is given here by the ion mass while the restoring force is provided by the relativistic electron degeneracy pressure, and the dispersion is due to the deviation from charge neutrality. A nonlinear Korteweg-de Vries equation is derived for small but finite amplitude waves and is used to study the properties of localized ion acoustic solitons for parameters relevant for dense astrophysical objects such as white dwarf stars. Different degrees of relativistic electron degeneracy are discussed and compared.

  • 40. Misra , A.P.
    et al.
    Shukla , P.K.
    Umeå universitet, Teknisk-naturvetenskaplig fakultet, Fysik.
    Bhowmik , C.
    Electron-acoustic solitary waves in dense quantum electron-ion plasmas2007Ingår i: Physics of Plasmas, ISSN 1070-664X, E-ISSN 1089-7674, Vol. 14, s. 82309-Artikel i tidskrift (Refereegranskat)
  • 41. Misra , A.P
    et al.
    Shukla, P. K.
    Umeå universitet, Teknisk-naturvetenskaplig fakultet, Fysik.
    Amplitude modulation of electron plasma oscillations in a dense electron-hole plasma2007Ingår i: Physics of Plasmas, ISSN 1070-664X, E-ISSN 1089-7674, Vol. 14, s. 82312-Artikel i tidskrift (Refereegranskat)
  • 42.
    Misra, Amar P
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Banerjee, S
    Haas, F
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Shukla, P K
    Assis, L P G
    Temporal dynamics in the one-dimensional quantum Zakharov equations for plasmas2010Ingår i: Physics of Plasmas, ISSN 1070-664X, E-ISSN 1089-7674, Vol. 17, nr 3, artikel-id 032307Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The temporal dynamics of the quantum Zakharov equations in one spatial dimension, which describes the nonlinear interaction of quantum Langmuir waves and quantum ion-acoustic waves, is revisited by considering their solution as a superposition of three interacting wave modes in Fourier space. Previous results in the literature are modified and rectified. Periodic, chaotic, and hyperchaotic behaviors of the Fourier-mode amplitudes are identified by the analysis of Lyapunov exponent spectra and the power spectrum. The periodic route to chaos is explained through a one-parameter bifurcation analysis. The system is shown to be destabilized via a supercritical Hopf-bifurcation. The adiabatic limits of the fully spatiotemporal and reduced systems are compared from the viewpoint of integrability properties.

  • 43.
    Misra, Amar P
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Brodin, Gert
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Marklund, Mattias
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Shukla, Padma K
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Generation of wakefields by whistlers in spin quantum magnetoplasmas2010Ingår i: Physics of Plasmas, ISSN 1070-664X, E-ISSN 1089-7674, Vol. 17, nr 12, artikel-id 122306Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The excitation of electrostatic wakefields in a magnetized spin quantum plasma by the classical and the spin-induced ponderomotive force (CPF and SPF, respectively) due to whistler waves is reported. The nonlinear dynamics of the whistlers and the wakefields is shown to be governed by a coupled set of nonlinear Schrodinger and driven Boussinesq-like equations. It is found that the quantum force associated with the Bohm potential introduces two characteristic length scales, which lead to the excitation of multiple wakefields in a strongly magnetized dense plasma (with a typical magnetic field strength B(0)greater than or similar to 10(9) T and particle density n(0)greater than or similar to 10(36) m(-3)), where the SPF strongly dominates over the CPF. In other regimes, namely, B(0)less than or similar to 10(8) T and n(0)less than or similar to 10(35) m(-3), where the SPF is comparable to the CPF, a plasma wakefield can also be excited self-consistently with one characteristic length scale. Numerical results reveal that the wakefield amplitude is enhanced by the quantum tunneling effect; however, it is lowered by the external magnetic field. Under appropriate conditions, the wakefields can maintain high coherence over multiple plasma wavelengths and thereby accelerate electrons to extremely high energies. The results could be useful for particle acceleration at short scales, i.e., at nanometer and micrometer scales, in magnetized dense plasmas where the driver is the whistler wave instead of a laser or a particle beam.

  • 44.
    Misra, Amar P
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Marklund, Mattias
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Brodin, Gert
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Shukla, Padma K
    RUB International Chair, International Centre for Advanced Studies in Physical Sciences, Faculty of Physics and Astronomy, Ruhr University Bochum, Bochum, Germany.
    Stability of two-dimensional ion-acoustic wave packets in quantum plasmas2011Ingår i: Physics of Plasmas, ISSN 1070-664X, E-ISSN 1089-7674, Vol. 18, nr 4, s. 042102-042109Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The nonlinear propagation of two-dimensional (2D) quantum ion-acoustic waves (QIAWs) is studied in a quantum electron–ion plasma. By using a 2D quantum hydrodynamic model and the method of multiple scales, a new set of coupled nonlinear partial differential equations is derived which governs the slow modulation of the 2D QIAW packets. The oblique modulational instability (MI) is then studied by means of a corresponding nonlinear Schrödinger equation derived from the coupled nonlinear partial differential equations. It is shown that the quantum parameter H (ratio of the plasmon energy density to Fermi energy) shifts the MI domains around the kθ -plane, where k is the carrier wave number and θ is the angle of modulation. In particular, the ion-acoustic wave (IAW), previously known to be stable under parallel modulation in classical plasmas, is shown to be unstable in quantum plasmas. The growth rate of the MI is found to be quenched by the obliqueness of modulation. The modulation of 2D QIAW packets along the wave vector k is shown to be described by a set of Davey–Stewartson-like equations. The latter can be studied for the 2D wave collapse in dense plasmas. The predicted results, which could be important to look for stable wave propagation in laboratory experiments as well as in dense astrophysical plasmas, thus generalize the theory of MI of IAW propagations both in classical and quantum electron–ion plasmas.

  • 45.
    Misra, Amar Prasad
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Shukla, Padma Kant
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Modulational instability and nonlinear evolution of two-dimensional electrostatic wave packets in ultra-relativistic degenerate dense plasmas2011Ingår i: Physics of Plasmas, ISSN 1070-664X, E-ISSN 1089-7674, Vol. 18, nr 4, artikel-id 042308Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We consider the nonlinear propagation of electrostatic wave packets in an ultra-relativistic (UR) degenerate dense electron-ion plasma, whose dynamics is governed by the nonlocal two-dimensional nonlinear Schrodinger-like equations. The coupled set of equations is then used to study the modulational instability (MI) of a uniform wave train to an infinitesimal perturbation of multidimensional form. The condition for the MI is obtained, and it is shown that the nondimensional parameter, beta proportional to lambda(C)n(0)(1/3) (where lambda(C) is the reduced Compton wavelength and n(0) is the particle number density) associated with the UR pressure of degenerate electrons, shifts the stable (unstable) regions at n(0) similar to 10(30)cm(-3) to unstable (stable) ones at higher densities, i.e., n(0) greater than or similar to 7 x 10(33). It is also found that the higher the values of n(0), the lower is the growth rate of MI with cut-offs at lower wave numbers of modulation. Furthermore, the dynamical evolution of the wave packets is studied numerically. We show that either they disperse away or they blowup in a finite time, when the wave action is below or above the threshold. The results could be useful for understanding the properties of modulated wave packets and their multidimensional evolution in UR degenerate dense plasmas, such as those in the interior of white dwarfs and/or pre-Supernova stars.

  • 46. Misra, AP
    et al.
    Shukla, Padma Kant
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik. Institut für Theoretische Physik IV and Centre for Plasma Science and Astrophysics, Fakultät für Physik and Astronomie, Ruhr-Universität Bochum, D-44780 Bochum, Germany; School of Physics, University of KwaZulu-Natal, 4000 Durban, South Africa; Nonlinear Physics Centre, Ruhr-Universität Bochum, D-44780 Bochum, Germany; Max-Planck Institut für Extraterrestrische Physik, D-85741 Garching, Germany; GoLP/Instituto de Plasmas e Fusao Nuclear, Instituto Superior T’ecnico, 1049-001 Lisboa, Portugal; CCLRC Centre for Fundamental Physics, Rutherford Appleton Laboratory, Chilton, Didcot, Oxon 0X11 0QX, United Kingdom; SUPA Department of Physics, University of Strathclyde, Glasgow G40NG, United Kingdom; Department of Physics, COMSATS Institute of Information Technology, Islamabad, Pakistan.
    Modulational instability of magnetosonic waves in a spin 1/2 quantum plasma2008Ingår i: Physics of Plasmas, ISSN 1070-664X, E-ISSN 1089-7674, Vol. 15, nr 5, artikel-id 052105Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The modulational instability (MI) of magnetosonic waves (MSWs) is analyzed, by using a two-fluid quantum magnetohydrodynamic model that includes the effects of the electron-1/2 spin and the plasma resistivity. The envelope modulation is then studied by deriving the corresponding nonlinear Schrodinger equation from the governing equations. The plasma resistivity is shown to play a dissipative role for the onset of MI. In the absence of resistivity, the microscopic spin properties of electrons can also lead to MI. In such a situation, the dominant spin contribution corresponds to a dense quantum plasma with the particle number density, n(0)greater than or similar to 10(28) m(-3). Also, in such a dissipative (absorbing) medium, where the group velocity vector is usually complex for real values of the wave vector, the role of the real group velocity in the propagation of one-dimensional MSW packets in a homogeneous absorbing medium is reported. The effects of quantum spin on the stability/instability conditions of the magnetosonic envelope are obtained and examined numerically. From the nonlinear dispersion relation of the modulated wave packet it is found that the effect of the spin (plasma resistivity) is to decrease (increase) the instability growth rate provided the normalized Zeeman energy does not exceed a critical value. The theoretical results may have relevance to astrophysical (e.g., magnetars) as well as to ultracold laboratory plasmas (e.g., Rydberg plasmas).

  • 47. Misra, AP
    et al.
    Shukla, Padma Kant
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik. Institut für Theoretische Physik IV and Centre for Plasma Science and Astrophysics, Fakultät für Physik and Astronomie, Ruhr-Universität Bochum, D-44780 Bochum, Germany; School of Physics, University of KwaZulu-Natal, 4000 Durban, South Africa; Nonlinear Physics Centre, Ruhr-Universität Bochum, D-44780 Bochum, Germany; Max-Planck Institut für extraterrestrische Physik, D-85741 Garching, Germany; GoLP/Instituto de Plasmas e Fusao Nuclear, Instituto Superior T’ecnico, 1049-001 Lisboa, Portugal; CCLRC Centre for Fundamental Physics, Rutherford Appleton Laboratory, Chilton, Didcot, Oxon 0X11 0QX, UK; SUPA Department of Physics, University of Strathclyde, Glasgow G40NG, UK; Department of Physics, COMSATS Institute of Information Technology, Islamabad, Pakistan.
    Relativistic modulational instability of electron-acoustic waves in an electron-pair ion plasma2008Ingår i: Physics of Plasmas, ISSN 1070-664X, E-ISSN 1089-7674, Vol. 15, nr 12, artikel-id 122107Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The modulational instability of finite amplitude electron-acoustic waves (EAWs) along the external magnetic field is studied in an electron-pair ion plasma. Accounting for the relativistic electron mass variation nonlinearity and the Boltzmann distribution of both positive and negative ions, new regimes for the relativistic modulational instability (MI) for the low frequency (below the electron gyrofrequency) short-wavelength (in comparison with the ion gyroradius) modes are obtained numerically. It is found that the presence of a significant fraction of negative ions suppresses the MI growth/decay rate for the modulated EAW packets. The results could be of important for understanding the origin of amplitude modulated EAW packets in space (e.g., Earth's magnetotail) as well as in laboratory plasmas.

  • 48. Modestov, M.
    et al.
    Bychkov, Vitaly
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Brodin, Gert
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Marklund, Mattias
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik. Department of Applied Physics, Chalmers University of Technology, Gothenburg, Sweden.
    Brandenburg, A.
    Evolution of the magnetic field generated by the Kelvin-Helmholtz instability2014Ingår i: Physics of Plasmas, ISSN 1070-664X, E-ISSN 1089-7674, Vol. 21, nr 7, s. 072126-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The Kelvin-Helmholtz instability in an ionized plasma is studied with a focus on the magnetic field generation via the Biermann battery (baroclinic) mechanism. The problem is solved by using direct numerical simulations of two counter-directed flows in 2D geometry. The simulations demonstrate the formation of eddies and their further interaction and merging resulting in a large single vortex. In contrast to general belief, it is found that the instability generated magnetic field may exhibit significantly different structures from the vorticity field, despite the mathematically identical equations controlling the magnetic field and vorticity evolution. At later stages of the nonlinear instability development, the magnetic field may keep growing even after the hydrodynamic vortex strength has reached its maximum and started decaying due to dissipation.

  • 49.
    Modestov, Mikhail
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Bychkov, Vitaly
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Betti, Riccardo
    Fusion Science Center and Laboratory for Laser Energetics, University of Rochester, 250 East River Road, Rochester, New York 14623, USA .
    Eriksson, Lars-Erik
    Department of Applied Mechanics, Chalmers University of Technology, 412 96 Göteborg, Sweden.
    Bubble velocity in the nonlinear Rayleigh-Taylor instability at a deflagration front2008Ingår i: Physics of Plasmas, ISSN 1070-664X, E-ISSN 1089-7674, Vol. 15, nr 4, s. 042703-042715Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The Rayleigh-Taylor instability at a deflagration front is studiedsystematically using extensive direct numerical simulations.  Itis shown that, for a sufficiently large gravitational field, theeffects of bubble rising dominate the deflagration dynamics. Itis demonstrated both analytically and numerically that thedeflagration speed is described asymptotically by the Layzertheory in the limit of large acceleration. In the opposite limitof small and zero gravitational field, intrinsic properties of thedeflagration front become important. In that case, the deflagrationspeed is determined by the velocity of a planar front and by theDarrieus-Landau instability. Because of these effects, thedeflagration speed is larger than predicted by theLayzer theory. An analytical formula for the deflagration speedis suggested, which matches two asymptotic limits of large andsmall acceleration. The formula is in good agreement withthe numerical data in a wide range of Froude numbers. Thepresent results are also in agreement with previous numericalsimulations on this problem.

  • 50.
    Modestov, Mikhail
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Bychkov, Vitaly
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Marklund, Mattias
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    The Rayleigh-Taylor instability in quantum magnetized plasma with para- and ferromagnetic properties2009Ingår i: Physics of Plasmas, ISSN 1070-664X, E-ISSN 1089-7674, Vol. 16, nr 3, s. 032106-032117Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We investigate influence of magnetic field on the Rayleigh–Taylor instability in quantum plasmas with para- and ferromagnetic properties. Magnetization of quantum plasma happens due to the collective electron spin behavior at low temperature and high plasma density. In the classical case, without magnetization, magnetic field tends to stabilize plasma perturbations with wave numbers parallel to the field and with sufficiently short wavelengths. Paramagnetic effects in quantum plasma make this stabilization weaker. The stabilization disappears completely for short wavelength perturbations in the ferromagnetic limit, when the magnetic field is produced by intrinsic plasma magnetization only. Still, for perturbations of long and moderate wavelength, certain stabilization always takes place due to the nonlinear character of quantum plasma magnetization.

12 1 - 50 av 76
RefereraExporteraLänk till träfflistan
Permanent länk
Referera
Referensformat
  • apa
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Annat format
Fler format
Språk
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Annat språk
Fler språk
Utmatningsformat
  • html
  • text
  • asciidoc
  • rtf