umu.sePublikationer
Ändra sökning
Avgränsa sökresultatet
23456 201 - 250 av 291
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
• 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
• Disputationsdatum (tidigaste först)
• Disputationsdatum (senaste först)
Markera
Maxantalet träffar du kan exportera från sökgränssnittet är 250. Vid större uttag använd dig av utsökningar.
• 201.
Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik. Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik. KTH, Stockholm. IRF-K, Kiruna. KTH, Stockholm. University of Leicester, UK. University of Leicester, UK.
Azimuthal velocity shear within an Earthward fast flow: further evidence for magnetotail untwisting?2015Ingår i: Annales Geophysicae, ISSN 0992-7689, E-ISSN 1432-0576, Vol. 33, s. 245-255Artikel i tidskrift (Refereegranskat)

It is well known that nonzero interplanetary magnetic field By conditions lead to a twisted magnetotail configuration. The plasma sheet is rotated around its axis and tail magnetic field lines are twisted, which causes an azimuthal displacementof their ionospheric footprints. According to the untwisting hypothesis, the untwisting of twisted field lines is suggested to influence the azimuthal direction of convective fast flows in the nightside geospace. However, there is a lack of in situ magnetospheric observations, which show actual signatures of the possible untwisting process. In this paper, we report detailed Cluster observations of an azimuthal flow shear across the neutral sheet associated with an Earthward fast flow on 5 September 2001. The observations show a flow shear velocity pattern with a Vperpy sign change, near the neutral sheet (Bx $\sim$ 0) within a fast flow during the neutral sheet flapping motion over the spacecraft. Firstly, this implies that convective fast flows may not generally be unidirectional across the neutral sheet, but may have a more complex structure. Secondly, in this event tail By and the flow shear are as expected by the untwisting hypothesis. The analysis of the flow shear reveals a linear dependence between Bx and Vperpy close to the neutral sheet and suggests that Cluster crossed the neutral sheet in the dawnward part of the fast flow channel. The magnetospheric observations are supported by the semi-empirical T96 and TF04 models. Furthermore, the ionospheric SuperDARN convection maps support the satellite observations proposing that the azimuthal component of the magnetospheric flows is enforced by a magnetic field untwisting. In summary,the observations give strong supportive evidence to the tail untwisting hypothesis. However, the T96 ionospheric mapping demonstrates the limitations of the model in mapping from a twisted tail.

• 202.
Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik. Institute of Space Sciences, Shandong University, Weihai, China.
Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik. Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
Convection electric field and plasma convection in a twisted magnetotail: t THEMIS case study 1-2 January 20092018Ingår i: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 123, nr 9, s. 7486-7497Artikel i tidskrift (Refereegranskat)

We investigate THEMIS satellite measurements made in a tail-aligned constellation during a time interval on 1-2 January 2009, which has previously been attributed to an interval of an interplanetary magnetic fieldB(y)-driven magnetotail twisting. We find evidence for that the orientation of the convection electric field in the tail is twist-mode dependent. For earthward flow and a negative twist (induced tail B-y < 0), the electric field is found to have northward E-z and tailward E-x components. During a positive twist (induced tail B-y > 0), the directions of E-z and E-x are reversed. The E-y component shows the expected dawn-to-dusk direction for earthward flow. The electric field components preserve their orientation across the neutral sheet, and a quasi-collinear field is observed irrespective to the tail distance. The electric field associated with the tailward flow has an opposite direction compared to the earthward flow for the negative twist. For the positive twist, the results are less clear. The corresponding plasma convection and thus the magnetic flux transport have an opposite dawn-dusk direction above and below the neutral sheet. The directions depend on the tail twist mode. The hemispherically asymmetric earthward plasma flows are suggested to be a manifestation of an asymmetric Dungey cycle in a twisted magnetotail. The role of tailward flows deserve further investigation.

• 203. Qin, Danfeng
Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik. Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik. Key Laboratory of Chemistry of Plant Resources in Arid Regions, State Key Laboratory Basis of Xinjiang indigenous medicinal plants resource utilization, Xinjiang Technical Institute of Physics and Chemistry, Chinese Academy of Science, Urumqi, China.
Three-dimensional carbon nanofiber derived from bacterial cellulose for use in a Nafion matrix on a glassy carbon electrode for simultaneous voltammetric determination of trace levels of Cd(II) and Pb(II)2017Ingår i: Microchimica Acta, ISSN 0026-3672, E-ISSN 1436-5073, Vol. 184, nr 8, s. 2759-2766Artikel i tidskrift (Refereegranskat)

The authors describe the preparation of carbon nanofibers (CNFs) with a three-dimensional network structure by one-step carbonization of bacterial cellulose at 800 degrees C. The 3D CNFs wrapped with Nafion polymer were cast on a glassy carbon electrode (GCE) which then enables sensitive detection of Cd(II) and Pb(II). Under optimized conditions and at typical stripping peaks of around -0.80 and -0.55 V (vs Ag/AgCl), the electrode exhibits high sensitivity and a wide analytical range of 2-100 mu g.L-1 for both Cd(II) and Pb(II). The detection limits are 0.38 mu g.L-1 for Cd(II) and 0.33 mu g.L-1 for Pb(II), respectively. The modified GCE was successfully employed to the determination of trace amounts of Cd(II) and Pb(II) in both tap water and waste water.

• 204.
Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik. Swedish Institute of Space Physics, Kiruna.
Ion escape from Mars: measurements in the present to understand the past2017Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)

Present-day Mars is a cold and dry planet with a thin CO2-dominated atmosphere comprising only a few ­­­mbar pressure at low altitudes. However, the Martian surface is marked with valley networks, hydrated mineral clays, carbonates and the remains of deltas and meandering rivers, i.e. traces of an active hydrological cycle present early in the planet's geological history. A strong greenhouse effect, and thus a thicker atmosphere, would have been required to sustain a sufficiently warm environment, particularly under the weaker luminosity of the early Sun. The fate of this early atmosphere is currently unknown.

While several mechanisms can remove atmospheric mass over time, a prominent hypothesis suggests that the lack of an intrinsic Earth-like global magnetic dipole has allowed the solar wind to erode the early Martian atmosphere by imparting energy to the planet's ionosphere which subsequently flows out as ion escape, over time depleting the greenhouse gasses and collapsing the ancient hydrological cycle. Previous studies have found insignificant ion escape rates under present-day conditions, however, the young Sun emitted significantly stronger solar wind and photoionizing radiation flux compared to the present. The geological record establishes the time of collapse of the hydrological cycle, estimated to have occurred in the mid-late Hesperian period (~3.3 billion years ago) at latest. To constrain the amount of atmosphere lost through ion escape since, we use the extensive database of ion flux measurements from the Analyzer of Space Plasmas and Energetic Atoms (ASPERA-3) particles package on the Mars Express orbiter (2004-present) to quantify the ion escape rate dependence on upstream solar wind and solar radiation conditions.

The Martian ion escape rate is shown to be insensitive to solar wind parameters with a weak inverse dependence on solar wind dynamic pressure, and linearly dependent on solar ionizing photon flux, indicating efficient screening of the bulk ionosphere by the induced magnetic fields. The impact of an extreme coronal mass ejection is studied and found to have no significant effect on the ion escape rate. Instead, intense solar wind is shown to only increase the escaping energy flux, i.e. total power of escaping ions, without increasing the rate by accelerating already escaping ions. The orientation of the strongest magnetized crustal fields are shown to modulate the ion escape rate, though to have no significant time-averaged effect. We also study the influence of solar wind and solar radiation on the major Martian plasma boundaries and discuss factors that might limit the ion escape rate, including solar wind-ion escape coupling, which is found to be ≲1% and decreasing with increased solar wind dynamic pressure. The significant escape rate dependencies found are extrapolated back in time, considering the evolution of solar wind and ionizing radiation, and shown to account for only 4.8 ± 1.1 mbar equivalent surface pressure loss since the time of collapse of the Martian hydrosphere in the Hesperian, with ~6 mbar as an upper estimate. Extended to the late Noachian period (3.9 billion years ago), the found dependencies can only account for ≲10 mbar removed through ion escape, an insignificant amount compared to the ≳1 bar surface pressure required to sustain a warm climate on early Mars.

• 205.
Swedish Institute of Space Physics, Kiruna.
Swedish Institute of Space Physics, Kiruna. Swedish Institute of Space Physics, Kiruna. Swedish Institute of Space Physics, Kiruna.
Solar wind- and EUV-dependent models for the shapes of the Martian plasma boundaries based on Mars Express measurements2017Ingår i: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 122, nr 7, s. 7279-7290Artikel i tidskrift (Refereegranskat)

The long operational life (2003-present) of Mars Express (MEX) has allowed the spacecraft tomake plasma measurements in the Martian environment over a wide range of upstream conditions. Wehave analyzed ∼7000 MEX orbits, covering three orders of magnitude in solar wind dynamic pressure, withdata from the on board Analyzer of Space Plasmas and Energetic Particles (ASPERA-3) package, mappingthe locations where MEX crosses the main plasma boundaries, induced magnetosphere boundary (IMB), ionosphere boundary (IB), and bow shock (BS). A coincidence scheme was employed, where data fromthe Ion Mass Analyzer (IMA) and the Electron Spectrometer (ELS) had to agree for a positive boundaryidentification, which resulted in crossings from 1083 orbit segments that were used to create dynamictwo-parameter (solar wind density, nsw, and velocity vsw) dependent global dynamic models for the IMB, IB,and BS. The modeled response is found to be individual to each boundary. The IMB scales mainly dependenton solar wind dynamic pressure and EUV intensity. The BS location closely follows the location of the IMB atthe subsolar point, though under extremely low nsw and vsw the BS assumes a more oblique shape. The IBclosely follows the IMB on the dayside and changes its nightside morphology with different trends for nswand vsw. We also investigate the influence of extreme ultraviolet (EUV) radiation on the IMB and BS, findingthat increased EUV intensity expands both boundaries.

• 206.
Swedish Institute of Space Physics, Kiruna.
Swedish Institute of Space Physics, Kiruna. Swedish Institute of Space Physics, Kiruna. Swedish Institute of Space Physics, Kiruna.
Effects of the crustal magnetic fields on the Martian atmospheric ion escape rate2016Ingår i: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 43, nr 20, s. 10574-10579Artikel i tidskrift (Refereegranskat)

Eight years (2007–2015) of ion flux measurements from Mars Express are used to statisticallyinvestigate the influence of the Martian magnetic crustal fields on the atmospheric ion escape rate.We combine all Analyzer of Space Plasmas and Energetic Atoms/Ion Mass Analyzer (ASPERA-3/IMA)measurements taken during nominal upstream solar wind and solar extreme ultraviolet conditions tocompute global average ion distribution functions, individually for the north/south hemispheres and forvarying solar zenith angles (SZAs) of the strongest crustal magnetic field. Escape rates are subsequentlycalculated from each of the average distribution functions. The maximum escape rate (4.2 ± 1.2) × 1024 s−1 is found for SZA = 60–80, while the minimum escape rate (1.7±0.6)×1024 s−1 is found for SZA = 28–60,showing that the dayside orientation of the crustal fields significantly affects the global escape rate (p=97%). However, averaged over time, independent of SZA, we find no statistically significant difference inthe escape rates from the two hemispheres (escape from southern hemisphere 46% ± 18% of global rate).

• 207.
Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik. Swedish Institute of Space Physics, Kiruna.
Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik. Swedish Institute of Space Physics, Kiruna. Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik. Swedish Institute of Space Physics, Kiruna. Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik. Swedish Institute of Space Physics, Kiruna. Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik. Swedish Institute of Space Physics, Kiruna.
Global Mars-solar wind coupling and ion escape2017Ingår i: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 122, nr 8, s. 8051-8062Artikel i tidskrift (Refereegranskat)

Loss of the early Martian atmosphere is often thought to have occurred due to an effective transfer of the solar wind energy through the Martian induced magnetic barrier to the ionosphere. We have quantified the coupling efficiency by comparing the power of the heavy ion outflow with the available power supplied by the upstream solar wind. Constraining upstream solar wind density nsw, velocity vsw, and EUV intensity IEUV/photoionizing flux FXUV in varying intervals reveals a decrease in coupling efficiency, k,with solar wind dynamic pressure as ∝ pdyn−0.74±0.13 and with FXUV as k ∝ FXUV−2.28±0.30. Despite the decreasein coupling efficiency, higher FXUV enhances the cold ion outflow, increasing the total ion escape rate as Q(FXUV) = 1010(0.82 ± 0.05)FXUV. The discrepancy between coupling and escape suggests that ion escapefrom Mars is primarily production limited in the modern era, though decreased coupling may lead to an energy-limited solar wind interaction under early Sun conditions.

• 208.
Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik. Swedish Institute of Space Physics, Kiruna.
Swedish Institute of Space Physics, Kiruna. Swedish Institute of Space Physics, Kiruna. Swedish Institute of Space Physics, Kiruna. Swedish Institute of Space Physics, Kiruna.
Ion escape from Mars through time: An extrapolation of atmospheric loss based on 10 years of Mars Express measurementsManuskript (preprint) (Övrigt vetenskapligt)

Solar wind driven atmospheric ion escape has long been hypothesized as a major influence on the evolution of the Martian atmosphere due to the lack of a Martian global dipole magnetic field. We use 10 years (2007-2017) of Mars Express data to quantify the ion escape rate over the full sampled upstream solar wind dynamic pressure, pdyn, and solar photoionizing flux, FXUV, parameter space. The modeled dependence on the upstream parameters indicates a near-linear dependence on FXUV and weak negative correlation with pdyn. Integrating total heavy ion escape back through time, considering the evolution of the upstream parameters and the modeled trends, can only account for an estimated 4.8 ± 1.1 mbar of atmosphere lost as ions since the mid-late Hesperian (3.3 Ga ago). Accounting for the recently reported stability of ion escape through the energetic oxygen ion plume provides an upper estimate of 6 mbar lost. Extending the extrapolation to the late Noachian (3.9 Ga ago) accounts for 6.3 ± 1.9 mbar, and analogously up to 9 mbar, lost through ion escape since. Thus the ion escape trends observed by Mars Express indicate that atmospheric ion escape contributed only a minor role in the evolution of the Martian atmosphere. We also report solar wind control of the cold ion outflow channel, providing a tentative explanation for the low response of the ion escape rate to upstream solar wind.

• 209.
Swedish Institute of Space Physics, Kiruna.
Swedish Institute of Space Physics, Kiruna. Swedish Institute of Space Physics, Kiruna. Swedish Institute of Space Physics, Kiruna. Swedish Institute of Space Physics, Kiruna.
The Martian atmospheric ion escape rate dependence on solar wind and solar EUV conditions: 1. Seven years of Mars Express observations2015Ingår i: Journal of Geophysical Research - Planets, ISSN 2169-9097, E-ISSN 2169-9100, Vol. 120, nr 7, s. 1298-1309Artikel i tidskrift (Refereegranskat)

More than 7 years of ion flux measurements in the energy range 10 eV–15 keV have allowed the ASPERA-3/IMA (Analyzer of Space Plasmas and Energetic Ions/Ion Mass Analyzer) instrument on Mars Express to collect a large database of ion measurements in the Mars environment, over a wide range of upstream solar wind (density and velocity) and radiation (solar EUV intensity) conditions. We investigate the influence of these parameters on the Martian atmospheric ion escape rate by integrating IMA heavy ionflux measurements taken in the Martian tail at similar (binned) solar wind density (nsw), velocity (vsw), and solar EUV intensity (IEUV) conditions. For the same solar wind velocity and EUV intensity ranges (vsw and IEUV constrained), we find a statistically significant decrease of up to a factor of 3 in the atmospheric ion escape rate with increased average solar wind density (5.6 × 1024 s−1 to 1.9 × 1024 s−1 for 0.4 cm−3 and 1.4 cm−3, respectively). For low solar wind density (0.1–0.5 cm−3) and low EUV intensity, the escape rate increaseswith increasing solar wind velocity from 2.4 × 1024 s−1 to 5.6 × 1024 s−1. During high solar EUV intensities the escape fluxes are highly variable, leading to large uncertainties in the estimated escape rates; however, a statistically significant increase in the escape rate is found between low/high EUV for similar solar wind conditions. Empirical-analytical models for atmospheric escape are developed by fitting calculated escape rates to all sufficiently sampled upstream conditions.

• 210.
Swedish Institute of Space Physics, Kiruna.
Swedish Institute of Space Physics, Kiruna. Swedish Institute of Space Physics, Kiruna. Swedish Institute of Space Physics, Kiruna. Swedish Institute of Space Physics, Kiruna. Swedish Institute of Space Physics, Kiruna.
Mars Under Primordial Solar Wind Conditions: Mars Express Observations of the Strongest CME Detected at Mars Under Solar Cycle #24 and its Impact on Atmospheric Ion Escape2017Ingår i: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007Artikel i tidskrift (Refereegranskat)

An extremely strong Coronal Mass Ejection (CME) impacted Mars on 12 July 2011, while theMars Express spacecraft was present inside the nightside ionosphere. Estimated solar wind density andspeed during the event are 39 particles cm−3 and 730 km/s, corresponding to nominal solar wind fluxat Mars when the solar system was ∼1.1 Ga old. Comparing with expected average atmospheric heavy ionfluxes under similar XUV conditions, the CME impact is found to have no significant effect on the escaperate 3.3 × 1024 s−1, with an upper limit at 1025 s−1 if the observed tail contraction is not taken into account.On the subsequent orbit, 7 h later after magnetosphere response, fluxes were only 2.4% of average. As such,even under primordial solar wind conditions we are unable to find support for a strong solar wind-driven ion escape, rather the main effect appears to be acceleration of the escaping ions by ×10–×20 typicalcharacteristic energy.

• 211.
Swedish Institute of Space Physics, Kiruna.
Swedish Institute of Space Physics, Kiruna. Swedish Institute of Space Physics, Kiruna. Swedish Institute of Space Physics, Kiruna. Department of Computer Science, Electrical and Space Engineering,Luleå University of Technology, Kiruna, Sweden.. Space Research Institute, Austrian Academy of Sciences, Graz, Austria..
Phobos 2/ASPERA data revisited: Planetary ion escape rate from Mars near the 1989 solar maximum2017Ingår i: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 40, nr 3, s. 477-481Artikel i tidskrift (Refereegranskat)

Insights about the near-Mars space environment from Mars Express observations have motivated a revisit of the Phobos 2/ASPERA ion data from 1989. We have expanded the analysis to now include all usable heavy ion(O+, O2+ , CO2+) measurements from the circular orbits of Phobos 2. Phobos 2/ASPERA ion fluxes in the Martian tailare compared with previous results obtained by the instruments on Phobos 2. Further validation of the measurement results is obtained by comparing IMP-8 and Phobos 2/ASPERA solar wind ion fluxes, taking into account the time lag between Earth and Mars. Heavy ion flux measurements from 18 circular equatorial orbits around Mars are bin-averaged to a grid, using the MSE (electric field) frame of reference. The binned data are subsequently integrated to determine the total escape rate of planetary ions. From this we derive a total planetary heavy ion escape rate of (2–3)$\times$1025 s-1 from Mars for the 1989 solar maximum.

• 212. Rao, Kavya H.
Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik. Australian Attosecond Science Facility, Centre for Quantum Dynamics, Grifﬁth University, Nathan, Queensland, Australia.
Time-resolved optical emission spectroscopic studies of picosecond laser produced Cr plasma2018Ingår i: Physics of Plasmas, ISSN 1070-664X, E-ISSN 1089-7674, Vol. 25, nr 6, artikel-id 063505Artikel i tidskrift (Refereegranskat)

Time-resolved optical emission spectroscopic measurements of a plasma generated by irradiating a Cr target using 60 picosecond (ps) and 300 ps laser pulses are carried out to investigate the variation in the line width (δλ) of emission from neutrals and ions for increasing ambient pressures. Measurements ranging from 10−6 Torr to 102 Torr show a distinctly different variation in the δλ of neutrals (Cr I) compared to that of singly ionized Cr (Cr II), for both irradiations. δλ increases monotonously with pressure for Cr II, but an oscillation is evident at intermediate pressures for Cr I. This oscillation does not depend on the laser pulse widths used. In spite of the differences in the plasma formation mechanisms, it is experimentally found that there is an optimum intermediate background pressure for which δλ of neutrals drops to a minimum. Importantly, these results underline the fact that for intermediate pressures, the usual practice of calculating the plasma number density from the δλ of neutrals needs to be judiciously done, to avoid reaching inaccurate conclusions.

• 213.
Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
Auroral Electron acceleration by Alfven waves and electrostatic fields2000Ingår i: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202, Vol. 105, nr A11, s. 25333-25344Artikel i tidskrift (Refereegranskat)

We present a two-dimensional numerical model for the formation of discrete auroral arcs. This model describes the evolution of shear Alfven waves generated by a growing force near the equatorial plane, and the transition to electrostatic fields when the force becomes stationary. The parallel electric fields on auroral field lines may be regarded as shear Alfven waves driven by a magnetospheric generator at zero frequency. In our collisionless model, precipitating auroral electrons are accelerated to an energy of 350 eV when the upward current is 3.1 mu Am-2. We also find that the electrostatic potential drop is proportional to the square of the current density.

• 214. Sabry, R
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 and Center for Plasma Science and Astrophysics, Ruhr-Universität Bochum, D-44780 Bochum, Germany; Max-Planck-Institut für Extraterrestrische Physik, D-85741 Garching, Germany; GoLP/Institute of Plasmas and Nuclear Fusion, Instituto Superior Técnico, 1049-001 Lisbon, Portugal; CCLRC Centre for Fundamental Physics, Rutherford Appleton Laboratory, Chilton, Didcot, Oxon 0X11 0QX, United Kingdom; SUPA Department of Physics, University of Strathclyde, Glasgow G 40NG, United Kingdom; School of Physics, Faculty of Science and Agriculture, University of Kwazulu-Natal, Durban 4000, South Africa.
Nonlinear wave modulation of cylindrical and spherical quantum ion-acoustic solitary waves2008Ingår i: Physics of Plasmas, ISSN 1070-664X, E-ISSN 1089-7674, Vol. 15, nr 12, artikel-id 122310Artikel i tidskrift (Refereegranskat)

Cylindrical and spherical amplitude modulation of quantum ion-acoustic (QIA) envelope solitary waves in a dense quantum plasma comprised of electrons and ions is investigated. For this purpose, a one-dimensional quantum hydrodynamic model and the Poisson equation are considered. By using the standard reductive perturbation technique, a modified nonlinear Schrodinger equation with the geometrical and the quantum effects is derived. The effect of quantum corrections and the effect due to the cylindrical and spherical geometries on the propagation of the QIA envelope solitary waves are examined. It is shown that there exists a modulation instability period depending on the quantum parameter, which does not exist for the one-dimensional classical case.

• 215. Sabry, R.
Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
Three-dimensional nonlinear Schrodinger equation in electron-positron-ion magnetoplasmas2011Ingår i: Physics of Plasmas, ISSN 1070-664X, E-ISSN 1089-7674, Vol. 18, nr 3, artikel-id 032302Artikel i tidskrift (Refereegranskat)

Three-dimensional ion-acoustic envelope soliton excitations in electron-positron-ion magnetoplasmas are interpreted. This is accomplished through the derivation of three-dimensional nonlinear Schrodinger equation, where the nonlinearity is balancing with the dispersive terms. The latter contains both an external magnetic field besides the usual plasma parameter effects. Based on the balance between the nonlinearity and the dispersion terms, the regions for possible envelope solitons are investigated indicating that new regimes for modulational instability of envelope ion-acoustic waves could be obtained, which cannot exist in the unmagnetized case. This will allow us to establish additional new regimes, different from the usual unmagnetized plasma, for envelope ion-acoustic waves to propagate in multicomponent plasma that may be observed in space or astrophysics.

• 216. Sabry, R.
Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
On the generation of envelope solitons in the presence of excess superthermal electrons and positrons2011Ingår i: Astrophysics and Space Science, ISSN 0004-640X, E-ISSN 1572-946X, Vol. 333, nr 1, s. 203-208Artikel i tidskrift (Refereegranskat)

A theoretical model is presented to investigate the existence, formation, and possible realization of nonlinear envelope ion acoustic solitary waves which accompany collisionless electron-positron-ion plasmas with high-energy electrons and positrons (represented by kappa distribution). By employing the reductive perturbation method, the hydrodynamic model and the Poisson equation are reduced to nonlinear Schrodinger equation. The effects of the superthermal parameters, as well as ion-to-electron temperature ratio on the propagation and stability of the envelope solitary waves are examined. The superthermal parameters (ion-to-electron temperature ratio) give rise to instability (stability) of the solitary excitations, since the instability window is strongly modified. Finally, the present results should elucidate the excitation of the nonlinear ion-acoustic solitary wave packets in superthermal electron-positron-ion plasmas, particularly in interstellar medium.

• 217. Sabry, R
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 structures: explosive, soliton, and shock in a quantum electron-positron-ion magnetoplasma2008Ingår i: Physics of Plasmas, ISSN 1070-664X, E-ISSN 1089-7674, Vol. 15, nr 12, artikel-id 122308Artikel i tidskrift (Refereegranskat)

Theoretical and numerical studies are performed for the nonlinear structures (explosive, solitons, and shock) in quantum electron-positron-ion magnetoplasmas. For this purpose, the reductive perturbation method is employed to the quantum hydrodynamical equations and the Poisson equation, obtaining extended quantum Zakharov-Kuznetsov equation. The latter has been solved using the generalized expansion method to obtain a set of analytical solutions, which reflects the possibility of the propagation of various nonlinear structures. The relevance of the present investigation to the white dwarfs is highlighted.

• 218. Sabry, R
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/Institute of Plasmas and Nuclear Fusion, 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.
Explosive and solitary excitations in a very dense magnetoplasma2008Ingår i: Physics Letters A, ISSN 0375-9601, E-ISSN 1873-2429, Vol. 372, nr 35, s. 5691-5694Artikel i tidskrift (Refereegranskat)

A two-component dense magnetoplasma consisting of ions and degenerate electrons is considered. The basic set of hydrodynamic and Poisson equations are reduced to the Zakharov-Kuznetsov (ZK) equation by using the reductive perturbation technique. The basic features of the electrostatic excitations are investigated by applying a new direct method to the ZK equation. It is found that the latter has new solutions, which admit the propagation of either solitary or explosive pulses. The relevance of the new direct method to other nonlinear partial differential equations is also discussed.

• 219. Sabry, R
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 and Center for Plasma Science and Astrophysics, Ruhr-Universität Bochum, D-44780 Bochum, Germany; Max-Planck-Institut für extraterrestrische Physik, D-85741 Garching, Germany; GoLP/Institute of Plasmas and Nuclear Fusion, 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 and Agriculture, University of Kwazulu-Natal, Durban 4000, South Africa; Department of Physics, CITT, Islamabad, Pakistan; National Center for Physics, Quaid-i-Azam University Campus, Islamabad, Pakistan.
Fully nonlinear ion-acoustic solitary waves in a plasma with positive-negative ions and nonthermal electrons2009Ingår i: Physics of Plasmas, ISSN 1070-664X, E-ISSN 1089-7674, Vol. 16, nr 3, artikel-id 032302Artikel i tidskrift (Refereegranskat)

Properties of fully nonlinear ion-acoustic solitary waves in a plasma with positive-negative ions and nonthermal electrons are investigated. For this purpose, the hydrodynamic equations for the positive-negative ions, nonthermal electron density distribution, and the Poisson equation are used to derive the energy integral equation with a new Sagdeev potential. The latter is analyzed to examine the existence regions of the solitary pulses. It is found that the solitary excitations strongly depend on the mass and density ratios of the positive and negative ions as well as the nonthermal electron parameter. Numerical solution of the energy integral equation clears that both positive and negative potentials exist together. It is found that faster solitary pulses are taller and narrower. Furthermore, increasing the electron nonthermality parameter (negative-to-positive ions density ratio) decreases (increases) the localized excitation amplitude but increases (decreases) the pulse width. The present model is used to investigate the solitary excitations in the (H+,O-2(-)) and (H+,H-) plasmas, where they are presented in the D- and F-regions of the Earth's ionosphere. This investigation should be helpful in understanding the salient features of the fully nonlinear ion-acoustic solitary waves in space and in laboratory plasmas where two distinct groups of ions and non-Boltzmann distributed electrons are present.

• 220. Sabry, R
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; National Center for Physics, Quaid-i-Azam University Campus, Islamabad, Pakistan; Nonlinear Physics Centre and Center for Plasma Science and Astrophysics, Ruhr-Universität Bochum, D-44780 Bochum, Germany; Max-Planck-Institut für extraterrestrische Physik, D-85741 Garching, Germany; GoLP/Institute of Plasmas and Nuclear Fusion, 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 and Agriculture, University of Kwazulu-Natal, Durban 4000, South Africa.
Cylindrical and spherical ion-acoustic envelope solitons in multicomponent plasmas with positrons2009Ingår i: Physical Review E. Statistical, Nonlinear, and Soft Matter Physics, ISSN 1539-3755, E-ISSN 1550-2376, Vol. 79, nr 5, artikel-id 056402Artikel i tidskrift (Refereegranskat)

The nonlinear wave modulation of planar and nonplanar (cylindrical and spherical) ion-acoustic envelope solitons in a collisionless unmagnetized electron-positron-ion plasma with two-electron temperature distributions has been studied. The reductive perturbative technique is used to obtain a modified nonlinear Schrodinger equation, which includes a damping term that accounts for the geometrical effect. The critical wave number threshold K(c), which indicates where the modulational instability sets in, has been determined for various regimes. It is found that an increase in the positron concentration (alpha) leads to a decrease in the critical wave number (K(c)) until alpha approaches certain value alpha(c) (critical positron concentration), then further increase in alpha beyond alpha(c) increases the value of K(c). Also, it is found that there is a modulation instability period for the cylindrical and spherical wave modulation, which does not exist in the one-dimensional case.

• 221. Sanchez-Cano, Beatriz
Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
Origin of the Extended Mars Radar Blackout of September 20172019Ingår i: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 124, nr 6, s. 4556-4568Artikel i tidskrift (Refereegranskat)

• 222. Schwab, M. B.
Max-Planck-Institut für Quantenoptik, Garching, Germany.
Few-cycle optical probe-pulse for investigation of relativistic laser-plasma interactions2013Ingår i: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 103, nr 19, artikel-id 191118Artikel i tidskrift (Refereegranskat)

The development of a few-cycle optical probe-pulse for the investigation of laser-plasma interactions driven by a Ti:sapphire, 30 Terawatt (TW) laser system is described. The probe is seeded by a fraction of the driving laser's energy and is spectrally broadened via self-phase modulation in a hollow core fiber filled with a rare gas, then temporally compressed to a few optical cycles via chirped mirrors. Shadowgrams of the laser-driven plasma wave created in relativistic electron acceleration experiments are presented with few-fs temporal resolution, which is shown to be independent of post-interaction spectral filtering of the probe-beam.

• 223. Shaikh, Dastgeer
Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik. Institut für Theoretische Physik IV, Ruhr-Universität Bochum, D-44780 Bochum, Germany; SUPA Department of Physics, University of Strathclyde, Glasgow G4 0NG, UK; Instituto de Plasmas e Fusão Nuclear, Instituto Superior Técnico, Universidade Técnica de Lisboa, 1049-001 Lisboa, Portugal.
3D electron fluid turbulence at nanoscales in dense plasmas2008Ingår i: New Journal of Physics, ISSN 1367-2630, E-ISSN 1367-2630, Vol. 10, artikel-id 083007Artikel i tidskrift (Refereegranskat)

We have performed three-dimensional (3D) nonlinear fluid simulations of electron fluid turbulence at nanoscales in an unmagnetized warm dense plasma in which mode coupling between wave function and electrostatic (ES) potential associated with underlying electron plasma oscillations (EPOs) lead to nonlinear cascades in inertial range. While the wave function cascades towards smaller length scales, ES potential follows an inverse cascade. We find from our simulations that the quantum diffraction effect associated with a Bohm potential plays a critical role in determining the inertial range turbulent spectrum and the subsequent transport level exhibited by the 3D EPOs.

• 224.
Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik. Also at the Grupo de Lasers e Plasmas, Instituto de Plasmas e Fusão Nuclear, Instituto Superior Técnico, Universidade Técnica de Lisboa, Lisbon, Portugal.
Polarization-force-induced dust grain acceleration and intrinsic magnetization of dusty plasmas2010Ingår i: Journal of Plasma Physics, ISSN 0022-3778, E-ISSN 1469-7807, Vol. 76, s. 677-680Artikel i tidskrift (Refereegranskat)

It is shown that the polarization force, arising from interactions between thermal ions and highly charged dust grains, can accelerate charged dust grains and can also create spontaneous magnetic fields in a quasi-neutral dusty plasma. The present results are relevant for understanding the origin of dust grain acceleration and the generation of spontaneous magnetic fields in cosmic dusty plasmas.

• 225.
Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
Generation of sheared flows by drift waves in a strongly magnetized electron-positron-ion plasma2011Ingår i: Journal of Plasma Physics, ISSN 0022-3778, E-ISSN 1469-7807, Vol. 77, s. 339-344Artikel i tidskrift (Refereegranskat)

It is shown that sheared/zonal flows (ZFs) can be nonlinearly excited by incoherent drift waves (DWs) in a strongly magnetized non-uniform plasma composed of electrons, positrons and ions. The dynamics of incoherent DWs in the presence of ZFs is governed by a wave-kinetic equation. The governing equation for ZFs in the presence of nonlinear forces (associated with nonlinear ion polarization and nonlinear ion-diamagnetic drifts) of the DWs is deduced by combining the Poisson equation, as well as the e-p-i continuity equations, together with appropriate plasma particle velocities in the DW and the ZF fields. Standard techniques are used to derive a nonlinear dispersion relation, which depicts two classes of the modulational instability of the DWs against the ZFs. Non-thermal ZFs can reduce the turbulent cross-field particle transport in non-uniform, strongly magnetized e-p-i plasmas.

• 226.
Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
Generation of zonal magnetic fields by drift waves in a current carrying nonuniform magnetoplasma2010Ingår i: Physics Letters A, ISSN 0375-9601, E-ISSN 1873-2429, Vol. 374, nr 24, s. 2461-2463Artikel i tidskrift (Refereegranskat)

It is shown that zonal magnetic fields (ZMFs) can be nonlinearly excited by incoherent drift waves (DWs) in a current carrying nonuniform magnetoplasma. The dynamics of incoherent DWs in the presence of ZMFs is governed by a wave-kinetic equation. The governing equation for ZMFs in the presence of nonlinear advection force of the DWs is obtained from the parallel component of the electron momentum equation and the Faraday law. Standard techniques are used to derive a nonlinear dispersion relation, which depicts instability via which ZMFs are excited in plasmas. ZMFs may inhibit the turbulent cross-field particle and energy transport in a nonuniform magnetoplasma.

• 227.
Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik. Grupo de Lasers e Plasmas, Instituto de Plasmas e Fusão Nuclear, Instituto Superior Técnico, Universidade Técnica de Lisboa, Portugal.
Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik. Max-Planck Institut für extraterrestrische Physik, Garching, Germany; Grupo de Lasers e Plasmas, Instituto de Plasmas e Fusão Nuclear, Instituto Superior Técnico, Universidade Técnica de Lisboa, Portugal; Science and Technology Facilities Council (STFC) Centre for Fundamental Physics, Rutherford Appleton Laboratory, Harwell Science and Innovation Campus, Chilton, Didcot, Oxfordshire, United Kingdom; Scottish Universities of Physics Alliance (SUPA), Department of Physics, University of Strathclyde, Glasgow, Scotland, United Kingdom; School of Physics, University of KwaZulu-Natal, Durban, South Africa.
Localized excitations in a nonlinearly coupled magnetic drift wave-zonal flow system2010Ingår i: Physics Letters A, ISSN 0375-9601, E-ISSN 1873-2429, Vol. 374, nr 13-14, s. 1514-1516Artikel i tidskrift (Refereegranskat)

We consider the amplitude modulation of the magnetic drift wave (MOW) by zonal flows (ZFs) in a nonuniform magnetoplasma. For this purpose, we use the two-fluid model to derive a nonlinear Schrodinger equation for the amplitude modulated MDWs in the presence of the ZF potential, and an evolution equation for the ZF potential which is reinforced by the nonlinear Lorentz force of the MDWs. Our nonlinearly coupled MDW-ZFs system of equations admits stationary solutions in the form of a localized MDW envelope and a shock-like ZF potential profile.

• 228.
Institut für Theoretische Physik IV, Fakultät für Physik und Astronomie, Ruhr-Universität Bochum, Bochum, Germany.
Proton-temperature-anisotropy-driven magnetic fields in plasmas with cold and relativistically hot electrons2010Ingår i: Journal of Plasma Physics, ISSN 0022-3778, E-ISSN 1469-7807, Vol. 76, s. 1-5Artikel i tidskrift (Refereegranskat)

We present a dispersion relation for a plane-polarized electromagnetic wave in plasmas composed of cold electrons, relativistically hot electrons and bi- Maxwellian protons. It is shown that the free energy in proton-temperature aniso- tropy drives purely growing electromagnetic modes in our three-component plasma. Expressions for the growth rates and thresholds of instabilities are presented. The present results are relevant for explaining the origin of spontaneously generated magnetic fields in laboratory and astrophysical plasmas.

• 229.
Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
The dust acoustic wave in a bounded dusty plasma with strong electrostatic interactions between dust grains2011Ingår i: Physics Letters A, ISSN 0375-9601, E-ISSN 1873-2429, Vol. 375, nr 17, s. 1809-1811Artikel i tidskrift (Refereegranskat)

The dispersion relation for the dust acoustic wave (DAW) in an unmagnetized dusty plasma cylindrical waveguide is derived, accounting for strong electrostatic interactions between charged dust grains. It is found that the boundary effect limits the radial extent of the DAW. The present result should be helpful for understanding the frequency spectrum of the DAW in a dusty plasma waveguide with strongly coupled charged dust grains.

• 230.
Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik. Institut für Theoretische Physik IV, Ruhr-Universität Bochum, Bochum, Germany; the Scottish Universities of Physics Alliance (SUPA), Department of Physics, University of Strathclyde, Glasgow, Scotland, UK; Grupo de Lasers e Plasmas, Instituto de Plasmas e Fusão Nuclear, Instituto Superior Técnico, Universidade Técnica de Lisboa, Lisbon, Portugal.
Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik. Department of Physics, Linköping University, Linköping, Sweden.
Potential distribution around a charged dust grain in an electronegative plasma2010Ingår i: Journal of Plasma Physics, ISSN 0022-3778, E-ISSN 1469-7807, Vol. 76, s. 673-676Artikel i tidskrift (Refereegranskat)

The potential distribution around a charged dust grain in an electronegative plasma is obtained by using the appropriate dielectric susceptibilities for the Boltzmann distributed electrons and negative ions, and for the inertial positive ions that are streaming from the bulk plasma into the electronegative plasma sheath. The existence of oscillatory ion wakefields is shown. Positive ions are trapped/focused in the ion wakefields, and subsequently the negative dust particles are attracted to each other, forming ordered dust structures.

• 231.
Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
Properties of electrostatic waves in ultracold neutral plasmas2010Ingår i: Physics Letters A, ISSN 0375-9601, E-ISSN 1873-2429, Vol. 374, nr 35, s. 3656-3657Artikel i tidskrift (Refereegranskat)

Properties of electrostatic waves in ultracold neutral plasmas (UNPs) are examined, taking accounting the polarization force arising from interactions between the thermal electrons and strongly coupled ions. It is found that the polarization force reduces the phase speed of the modified dispersive ion-acoustic (M-DIA) wave in UNPs. Possibility of the ion-lattice formation in the presence of the M-DIA wave is discussed.

• 232.
Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik. Faculty of Physics and Astronomy, Ruhr University Bochum, D-44780 Bochum, Germany; GoLP/Instituto de Plasmas e Fusao Nuclear, Instituto Superior Técnico, 1049-001 Lisboa, Portugal; SUPA Department of Physics, University of Strathclyde, Glasgow, Scotland; School of Physics, University of KwaZulu-Natal, Durban, South Africa; Department of Physics, COMSATS Institute of Information Technology, Islamabad, Pakistan.
A note on the formation of large-scale structures in the Universe2008Ingår i: Physica Scripta, ISSN 0031-8949, E-ISSN 1402-4896, Vol. 77, nr 6, artikel-id 068201Artikel i tidskrift (Refereegranskat)

A general dispersion relation for low-frequency electrostatic waves in a self-gravitating pair ion-dust plasma is derived. The dispersion relation admits two classes of the Jeans instability. The growth rates and thresholds of the latter are obtained. The implication of the present work to the formation of large-scale structures in the dusty universe is highlighted.

• 233.
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, and Centre for Fundamental Physics, Rutherford Appleton Laboratory, Chilton, Didcot, Oxon 0X11 0QX, United Kingdom.
Acceleration of ions by the radiation pressure in a magnetized electron-positron-ion plasma2006Ingår i: Journal of Plasma Physics, ISSN 0022-3778, E-ISSN 1469-7807, Vol. 72, nr 2, s. 159-162Artikel i tidskrift (Refereegranskat)

It is shown that the ponderomotive force of magnetic-field aligned circularly polarized electromagnetic waves can create space charge electric fields in a magnetized electron-positron-ion plasma. The space charge electric fields can; in turn, accelerate ions. Possible applications to the origin of energetic ions in laboratory plasmas and astrophysical settings axe discussed.

• 234.
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; School of Physics, University of KwaZulu-Durban, Durban 4000, South Africa; The Nonlinear Physics Centre & Centre for Plasma Science and Astrophysics, Ruhr-Universität Bochum, D-44780 Bochum, Germany; Max-Planck-Institut für extraterrestrische Physik, D-85741 Garching, Germany; Grupo de Lasers e Plasmas, Departamento de Física do Instituto Superior Técnico, Universidade Técnica de Lisboa, 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 G4 0NG, UK.
Compressional magnetoacoustic waves in a quantum dusty magnetoplasma2008Ingår i: Journal of Plasma Physics, ISSN 0022-3778, E-ISSN 1469-7807, Vol. 74, nr 1, s. 107-110Artikel i tidskrift (Refereegranskat)

The linear dispersion relation for compressional magnetoacoustic waves in a quantum magnetoplasma, is derived, taking into account the quantum Bohm potential and the rnagnetization of electrons due to the electron-1/2 spin effect. It is found that the quantum forces produce the wave dispersion at quantum scales, which depend on the external magnetic field strength.

• 235.
Institut für Theoretische Physik IV, Ruhr-Universität Bochum, D-44780 Bochum, Germany.
Excitation of electrostatic ion-cyclotron-like modes by the electron density ripple in dusty magnetoplasmas2009Ingår i: Journal of Plasma Physics, ISSN 0022-3778, E-ISSN 1469-7807, Vol. 75, s. 433-436Artikel i tidskrift (Övrigt vetenskapligt)

It is shown that electrostatic ion-eyelotron (EIC)-like modes can be excited by the pre-existing electron density ripple across the external magnetic field in a dusty magnetoplasma. For this purpose, we use the ion continuity and momentum equations, together with the Boltzmann-distributed electrons, and derive the standard Mathieu equation. The latter admits unstable solutions, demonstrating that the EIC-like modes in dusty magnetoplasms can be driven due to the free energy in the electron density ripple. the electron density ripple.

• 236.
Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik. Institut für Theoretische Physik IV, Ruhr-Universität Bochum, D-44780 Bochum, Germany; Scottish Universities Physics Alliance Department of Physics, University of Strathclyde, Glasgow, Scotland; Centre for Fundamental Physics, Rutherford Appleton Laboratory, Chilton, Didcot, UK; GoLP/Instituto de Plasmas e Fusão Nuclear, Instituto Superior Técnico, 1049-001 Lisboa, Portugal; School of Physics, University of KwaZulu-Natal, 4000 Durban, South Africa.
Excitation of ion wakefields by electromagnetic pulses in dense plasmas2009Ingår i: Journal of Plasma Physics, ISSN 0022-3778, E-ISSN 1469-7807, Vol. 75, nr 1, s. 15-18Artikel i tidskrift (Övrigt vetenskapligt)

The excitation of electrostatic ion wakefields by electromagnetic pulses in a very dense plasma is considered. For this purpose a wave equation for the ion wakefield in the presence of the ponderomotive force of the electromagnetic waves is obtained. Choosing a typical profile for the electromagnetic pulse, the form of the ion wakefields is deduced. The electromagnetic wave-generated ion wakefields can trap protons and accelerate them to high energies in dense plasmas.

• 237.
Institut für Theoretische Physik IV, Ruhr-Universität Bochum, D-44780 Bochum, Germany.
Excitation of the dust ion-acoustic and dust acoustic-like perturbations by plasma density ripples2009Ingår i: Physics Letters A, ISSN 0375-9601, E-ISSN 1873-2429, Vol. 373, nr 20, s. 1768-1770Artikel i tidskrift (Refereegranskat)

It is shown that the dust ion-acoustic (DIA) and dust acoustic (DA)-like perturbations can be excited by the electron density and ion density ripples, respectively. For this purpose, we use the relevant equations for the DIA and DA-like disturbances and derive the standard Mathieu equation. The latter admits unstable solutions, demonstrating that both the DIA and DA-like mode can be driven on account of the free energy in the plasma density ripples.

• 238.
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; Department of Electrical and Computer Engineering, University of California, San Diego, La Jolla, California 92003; Innovative Science Applications and Technology, Via S. Pellico 19, Saluzzo, Italy; Centre for Interdisciplinary Plasma Science, Max-Planck Institut für Plasma Physik und extraterrestrische Physik, D-85740 Garching, Germany; GOLP, Instituto Superior Técnico, Universidade Técnica de Lisboa, 1096 Lisboa Codex, Portugal; Centre for Fundamental Physics, Rutherford Appleton Laboratory, Chilton, Didcot, Oxfordshire, OX 11 OQX, UK.
Excitation of zonal flows by kinetic Alfven waves2005Ingår i: Physics of Plasmas, ISSN 1070-664X, E-ISSN 1089-7674, Vol. 12, nr 1, artikel-id 012310Artikel i tidskrift (Refereegranskat)

Nonlinear couplings between dispersive kinetic Alfven waves (DKAWs) and electrostatic,convective cells/zonal flows are reexamined. A set of equations that exhibit nonlinear couplings between the scalar and parallel vector potentials of the DKAWs and the scalar potential of zonal flows that are reinforced by the Reynolds stresses of the DKAWs in a magnetized plasma is presented. The equations are then Fourier-analyzed to obtain the nonlinear dispersion relation. The latter exhibits modulational instabilities, which could be responsible for enhanced zonal flows in a uniform magnetized plasma. Zonal flows can regulate the transport of plasma particles in laboratory magnetoplasmas as well as in the Earth's magnetosphere and in the solar corona.

• 239.
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; School of Physics, University of KwaZulu-Durban, Durban 4000, South Africa; Nonlinear Physics Centre & Centre for Plasma Science and Astrophysics, Ruhr-Universität Bochum, D-44780 Bochum, Germany; Max-Planck-Institut für extraterrestrische Physik, D-85741 Garching, Germany; Grupo de Lasers e Plasmas, Departamento de Física do Instituto Superior Técnico, Universidade Técnica de Lisboa, 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 G 40NG, UK.
Extraordinary electromagnetic waves in a warm dense magnetoplasma2007Ingår i: Physics Letters A, ISSN 0375-9601, E-ISSN 1873-2429, Vol. 369, nr 4, s. 312-314Artikel i tidskrift (Refereegranskat)

The linear dispersion relation for elliptically polarized electromagnetic waves in a dense fermionic quantum magnetoplasma is derived, taking into account the quantum forces associated with the quantum Bohm potential and the magnetization energy of the electrons due to the 1/2-electron spin effect. It is found that the quantum forces modify the wave dispersion at scales that depend upon lambda(q) = h/2m V-F and lambda B = root h/2mw(c), where h is the Planck constant divided by 2 pi, m is the electron mass, V-F is the Fermi electron thermal speed, and w(c) is the electron gyrofrequency.

• 240.
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; School of Physics, University of Kwazulu-Natal, Durban 4000, South Africa; Nonlinear Physics Centre & Centre for Plasma Science and Astrophysics, Ruhr-Universität Bochum, D-44780 Bochum, Germany; Max-Planck-Institut für Extraterrestrische Physik, D-85741 Garching, Germany; Grupo de Lasers e Plasmas, Departamento de Física do Instituto Superior Técnico, Universidade Técnica de Lisboa, 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 G 40NG, UK.
Generation and dynamics of plasma blobs in partially ionized tokamak scrape-off-layer2007Ingår i: Physics Letters A, ISSN 0375-9601, E-ISSN 1873-2429, Vol. 371, nr 5-6, s. 453-456Artikel i tidskrift (Refereegranskat)

A theoretical model for the generation and dynamics of plasma blobs in a tokamak scrape-off-layer (SOL) is presented. Specifically, it is suggested that plasma blobs could be generated due to a resistive Rayleigh-Taylor (RRT) instability in partially ionized SOL plasmas that contain equilibrium density and magnetic field inhomogeneities. By using the two-fluid model, a set of nonlinear equations for the low-frequency (in comparison with the ion gyrofrequency) electrostatic modes involved in the RRT instability is derived. In the linear limit, a new dispersion relation is obtained, and analyzed in some limiting cases. The nonlinear equations are useful for studying the dynamics of nonlinearly interacting finite amplitude RRT modes, which are linearly excited due to combined action of ionization as well as of density and magnetic field inhomogeneities in partially ionized SOL plasmas.

• 241.
Institut für Theoretische Physik IV, Fakultät für Physik und Astronomie, Ruhr-Universität Bochum, D-44780 Bochum, Germany.
Generation of magnetic fields by the non-stationary ponderomotive force of electromagnetic waves in plasmas with streaming electrons2009Ingår i: Physics Letters A, ISSN 0375-9601, E-ISSN 1873-2429, Vol. 373, nr 20, s. 1771-1772Artikel i tidskrift (Refereegranskat)

It is shown that the non-stationary ponderomotive force of large amplitude electromagnetic waves in plasmas with streaming electrons can spontaneously create magnetic fields. The present result may account for the magnetic fields in laser-produces plasmas, in cosmic plasmas, as well as in galactic and inter-galactic spaces.

• 242.
Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik. Institut für Theoretische Physik IV, Ruhr-Universität Bochum D-44780 Bochum, Germany; Scottish Universities Physics Alliance Department of Physics, University of Strathclyde, Glasgow, Scotland; Centre for Fundamental Physics, Rutherford Appleton Laboratory, Chilton, Didcot, UK; GoLP/Instituto de Plasmas e Fusão Nuclear, Instituto Superior Técnico, 1049-001 Lisboa, Portugal; School of Physics, University of KwaZulu-Natal, 4000 Durban, South Africa.
Generation of wakefields by electromagnetic waves in a magnetized electron-positron-ion plasma2009Ingår i: Plasma Physics and Controlled Fusion, ISSN 0741-3335, E-ISSN 1361-6587, Vol. 51, nr 2, artikel-id 024013Artikel i tidskrift (Refereegranskat)

The generation of electrostatic wakefields by an ordinary mode radiation and a magnetic field-aligned circularly polarized electromagnetic (CPEM) wave in a magnetized electron-positron-ion (e-p-i) plasma is considered. It is found that the presence of the ions is essential for the generation of upper-hybrid wakefields by the ordinary mode radiation, while the magnetic field-aligned electron plasma wakefields are created by the ponderomotive force of CPEM only if either the ions or the external magnetic field is present in an e-p-i magnetoplasma. The electromagnetic wave generated wakefields can trap both the electrons and the positrons and accelerate them to very high energies.

• 243.
Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik. Institut für Theoretische Physik IV, Ruhr-Universität Bochum, D-44780 Bochum, Germany; Scottish Universities Physics Alliance (SUPA), Department of Physics, University of Strathclyde, Glasgow G4 0NG, UK; GoLP/Instituto de Plasmas Fusão Nuclear, Instituto Superior Técnico, Universidade Técnica de Lisboa, 1049-001 Lisboa, Portugal; School of Physics, University of KwaZulu-Natal, 4000 Durban, South Africa; Max-Planck Institut für extraterrestrische Physik, D-85740 Garching, Germany.
Instability of short wavelength electrostatic electron-cyclotron modes in the presence of an ion density ripple in plasmas2009Ingår i: Physica Scripta, ISSN 0031-8949, E-ISSN 1402-4896, Vol. 80, nr 3, artikel-id 038201Artikel i tidskrift (Refereegranskat)

It is shown that short wavelength (in comparison with the ion thermal gyroradius), high-frequency (HF) electrostatic electron-cyclotron (EEC) modes can be excited by the pre-existing ion density ripple across the external magnetic field in a dusty magnetoplasma. For this purpose, we use the Boltzmann distributed ion density perturbation, together with the electron continuity and momentum equations, and derive the standard Mathieu equation. The latter admits unstable solutions, demonstrating that the short wavelength HF-EEC-like modes in dusty magnetoplasmas can be driven due to the free energy in the ion density ripple.

• 244.
Institut für Theoretische Physik IV, Ruhr-Universität Bochum, D-44780 Bochum, Germany.
Ion acceleration by the space charge electric force arising from the radiation pressure in a magnetized electron-positron plasma2009Ingår i: Physics Letters A, ISSN 0375-9601, E-ISSN 1873-2429, Vol. 373, nr 39, s. 3547-3549Artikel i tidskrift (Refereegranskat)

It is shown that ions can be accelerated by the space charge electric force arising from the separation of electrons and positrons due to the ponderomotive force of the magnetic field-aligned circularly polarized electromagnetic (CPEM) wave in a magnetized electron-positron-ion plasma. The ion acceleration critically depends on the external magnetic field strength. The result is useful in understanding differential ion acceleration in magnetized electron-positron-ion plasmas, such as those in magnetars and in some laboratory experiments that aim to mimic astrophysical environments.

• 245.
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.
Magnetization of a pair-ion plasma2005Ingår i: Physics Letters A, ISSN 0375-9601, E-ISSN 1873-2429, Vol. 341, nr 1-4, s. 184-186Artikel i tidskrift (Refereegranskat)

It is shown that ion temperature anisotropy in a pair-ion plasma can spontaneously create purely growing magnetic fields via a Weibel instability. The dispersion relation and the growth rate are presented.

• 246.
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; School of Physics, University of KwaZulu-Natal, Durban 4000, South Africa; Nonlinear Physics Centre & Centre for Plasma Science and Astrophysics, Ruhr-Universität Bochum, D-44780 Bochum, Germany; Max-Planck-Institut für extraterrestrische Physik, D-85741 Garching, Germany; Grupo de Lasers e Plasmas, Departamento de Física do Instituto Superior Técnico, Universidade Técnica de Lisboa, 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 G 40NG, UK.
Purely growing electromagnetic mode driven by ion-temperature anisotropy in a collisional plasma2007Ingår i: Physics Letters A, ISSN 0375-9601, E-ISSN 1873-2429, Vol. 370, nr 3-4, s. 316-318Artikel i tidskrift (Refereegranskat)

We derive a linear dispersion relation for plane polarized electromagnetic waves in an unmagnetized collisional plasma containing ion-temperature anisotropy. It is found that the free energy stored in the latter can be coupled to a purely growing electromagnetic mode via electron-neutral collisions. Expressions for the growth rate and the corresponding threshold of our new instability are presented.

• 247.
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; CCLRC, Centre for Fundamental Physics, Rutherford Appleton Laboratory, Chilton, Didcot, Oxon 0X11 0QX, United Kingdom; SUPA, Department of Physics, University of Strathclyde, Glasgow G 40NG, United Kingdom.
Dispersive electromagnetic drift modes in nonuniform quantum magnetoplasmas2006Ingår i: Physics of Plasmas, ISSN 1070-664X, E-ISSN 1089-7674, Vol. 13, nr 8, artikel-id 082101Artikel i tidskrift (Refereegranskat)

The existence of new electromagnetic drift modes in nonuniform quantum magnetoplasmas is predicted. For this purpose, new dispersion relations are derived by employing the quantum magnetohydrodynamic equation for plasmas without and with ion motions. The effects of electron corrections due to quantum fluctuations, density gradients, and external magnetic field strengths on the angular wave frequencies and growth/damping rates are examined. The present analytical and numerical investigations are relevant to dense astrophysical objects.

• 248.
Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik. Institut für Theoretische Physik IV and the Centre of Excellence for Plasma Science and Astrophysics, Fakultät für Physik und Astronomie, Ruhr-Universität Bochum, D-44780 Bochum, Germany; Department of Physics, University of Strathclyde, Glasgow, Scotland G4ONG, UK; Centro de Física dos Plasmas, Departamento de Fisica, Instituto Superior Técnico, Universidade Técnica de Lisboa, 1049-001 Lisbon, Portugal; and Centre for Fundamental Physics, Rutherford Appleton Laboratory, Chilton, Didcot, Oxfordshire, 0X11 OQX, UK.
Electron parallel-flow shear driven low-frequency electromagnetic modes in collisionless magnetoplasma2006Ingår i: Physics of Plasmas, ISSN 1070-664X, E-ISSN 1089-7674, Vol. 13, nr 5, artikel-id 052115Artikel i tidskrift (Refereegranskat)

The free energy associated with shear in the equilibrium parallel electron velocity is shown to be responsible for the excitation of low-frequency electromagnetic waves in collisionless magnetoplasma. New dispersion relations are derived by using the hydrodynamic equations for the electron fluid, the magnetic-field-aligned (parallel) drift of which varies in one of the perpendicular directions, and by using a kinetic ion model, together with Ampere's law and Poisson's equation. The dispersion relations are analyzed both analytically and numerically for a set of parameters representative of a laboratory experiment. New filamentary instabilities are predicted.

• 249.
Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik. Institut für Theoretische Physik IV and Centre 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; Centre for Fundamental Physics, Rutherford Appleton Laboratory, Chilton, Didcot, Oxon 0X11 0QX, UK; and Department of Physics, University of Strathclyde, Glasgow, Scotland G4 ONG, UK.
Radiation condensation instability of compressional electromagnetic modes in magnetoplasmas containing charged dust impurities2006Ingår i: Plasma Physics and Controlled Fusion, ISSN 0741-3335, E-ISSN 1361-6587, Vol. 48, nr 5, s. 509-514Artikel i tidskrift (Refereegranskat)

We report on an investigation into the radiation condensation ( RC) instability of low-frequency ( in comparison with the electron gyrofrequency) compressional electromagnetic waves in a magnetized plasma containing charged dust impurities. By using a two-fluid model, supplemented by the Faraday and Ampere laws, we derive a new dispersion relation. The latter is numerically analysed to examine the role of charged dust grains on the growth rate of the RC instability. The relevance of our investigation to density condensation in the next generation tokamak edges and on solar prominences is discussed.

• 250.
Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik. Fakultät für Physik und Astronomie, Institut für Theoretische Physik IV, Ruhr-Universität Bochum, D-44780 Bochum, Germany; Centro de Fisica dos Plasmas, Instituto Superior Técnico, Universidade Técnica de Lisboa, 1096 Lisboa Codex, Portugal; Centre for Fundamental Physics, Rutherford Appleton Laboratory, Chilton, Didcot, Oxfordshire OX11 0QX, United Kingdom; and the Department of Electrical and Computer Engineering, University of California San Diego, La Jolla, CA 92003-0407, USA.
Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
Low-frequency compressional electromagnetic waves in a nonuniform dusty magnetoplasma2005Ingår i: Physics Letters A, ISSN 0375-9601, E-ISSN 1873-2429, Vol. 337, nr 4-6, s. 419-424Artikel i tidskrift (Refereegranskat)

Dispersion properties of low-frequency (in comparison with the ion gyrofrequency) compressional electromagnetic waves in a nonuniform dusty magnetoplasma are presented. By using the plasma hydrodynamic equations together with the Faraday and Amp re laws, we derive a new dispersion relation. The latter is analyzed to show the relationship between various wave modes in dusty plasmas. The results should be useful in understanding the features of compressional electromagnetic waves in nonuniform astrophysical and laboratory dusty magnetoplasmas.

23456 201 - 250 av 291
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