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  • 1. Abdelsalam, UM
    et al.
    Moslem, WM
    Shukla, Padma Kant
    Umeå University, Faculty of Science and Technology, Department of Physics. 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.
    Ion-acoustic solitary waves in a dense pair-ion plasma containing degenerate electrons and positrons2008In: Physics Letters A, ISSN 0375-9601, E-ISSN 1873-2429, Vol. 372, no 22, p. 4057-4061Article in journal (Refereed)
    Abstract [en]

    Fully nonlinear propagation of ion-acoustic solitary waves in a collisionless dense/quantum electron-positron-ion plasma is investigated. The electrons and positrons are assumed to follow the Thomas-Fermi density distribution and the ions are described by the hydrodynamic equations. An energy balance-like equation involving a Sagdeev-type pseudo-potential is derived. Finite amplitude solutions are obtained numerically and their characteristics are discussed. The small-but finite-amplitude limit is also considered and an exact analytical solution is obtained. The present studies might be helpful to understand the excitation of nonlinear ion-acoustic solitary waves in a degenerate plasma such as in superdense white dwarfs.

  • 2. Abdelsalam, UM
    et al.
    Moslem, WM
    Shukla, Padma Kant
    Umeå University, Faculty of Science and Technology, Department of Physics. 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 electrons2008In: Physics of Plasmas, ISSN 1070-664X, E-ISSN 1089-7674, Vol. 15, no 5, article id 052303Article in journal (Refereed)
    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.

  • 3. Adhikary, N C
    et al.
    Misra, Amar P
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Bailung, H
    Chutia, J
    Ion-beam driven dust ion-acoustic solitary waves in dusty plasmas2010In: Physics of Plasmas, ISSN 1070-664X, E-ISSN 1089-7674, Vol. 17, no 4, article id 044502Article in journal (Refereed)
    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.

  • 4. Aikio, Anita T.
    et al.
    Pitkänen, Timo
    Fontaine, Dominic
    Dandouras, Iannis
    Amm, Olaf
    Kozlovsky, Alexander
    Vaivads, Andris
    Fazakerley, Andrew
    EISCAT and Cluster observations in the vicinity of the dynamical polar cap boundary2008In: Annales Geophysicae, ISSN 0992-7689, E-ISSN 1432-0576, Vol. 26, p. 87-105Article in journal (Refereed)
  • 5.
    Aikio, Anita T.
    et al.
    Department of Physical Sciences, University of Oulu, Finland.
    Pitkänen, Timo
    Department of Physical Sciences, University of Oulu, Finland.
    Fontaine, Dominic
    CETP/UVSQ, Velizy, France.
    Dandouras, Iannis
    CESR/CNRS, Toulouse, France.
    Amm, Olaf
    Finnish meteorological Institute, Helsinki, Finland.
    Kozlovsky, Alexander
    Department of Physical Sciences, University of Oulu, Finland; Sodankylä Geophysical Observatory, Sodankylä, Finland.
    Vaivads, Andris
    Swedish Institute of Space Physics, Ångströmlaboratoriet, Uppsala, Sweden.
    Fazakerley, Andrew
    Mullard Space Science Laboratory, University College, London, UK.
    EISCAT and Cluster observations in the vicinity of the dynamical polar cap boundary2008In: Annales Geophysicae, ISSN 0992-7689, E-ISSN 1432-0576, Vol. 26, p. 87-105Article in journal (Refereed)
    Abstract [en]

    The dynamics of the polar cap boundary and auroral oval in the nightside ionosphere are studied during late expansion and recovery of a substorm from the region between Tromsø (66.6 degree cgmLat) and Longyearbyen (75.2 degree cgmLat) on 27 February 2004 by using the coordinated EISCAT incoherent scatter radar, MIRACLE magnetometer and Cluster satellite measurements. During the late substorm expansion/early recovery phase, the polar cap boundary (PCB) made zig-zag-type motion with amplitude of 2.5 degree cgmLat and period of about 30 min near magnetic midnight. We suggest that the poleward motions of the PCB were produced by bursts of enhanced reconnection at the near-Earth neutral line (NENL). The subsequent equatorward motions of the PCB would then represent the recovery of the merging line towards the equilibrium state (Cowley and Lockwood, 1992). The observed bursts of enhanced westward electrojet just equatorward of the polar cap boundary during poleward expansions were produced plausibly by particles accelerated in the vicinity of the neutral line and thus lend evidence to the Cowley-Lockwood paradigm.

    During the substorm recovery phase, the footpoints of the Cluster satellites at a geocentric distance of 4.4RE mapped in the vicinity of EISCAT measurements. Cluster data indicate that outflow of H+ and O+ ions took place within the plasma sheet boundary layer (PSBL) as noted in some earlier studies as well. We show that in this case the PSBL corresponded to a region of enhanced electron temperature in the ionospheric F region. It is suggested that the ion outflow originates from the F region as a result of increased ambipolar diffusion. At higher altitudes, the ions could be further energized by waves, which at Cluster altitudes were observed as BBELF (broad band extra low frequency) fluctuations.

    The four-satellite configuration of Cluster revealed a sudden poleward expansion of the PSBL by 2 degree during ˜ 5 min. The beginning of the poleward motion of the PCB was associated with an intensification of the downward FAC at the boundary. We suggest that the downward FAC sheet at the PCB is the high-altitude counterpart of the Earthward flowing FAC produced in the vicinity of the magnetotail neutral line by the Hall effect (Sonnerup, 1979) during a short-lived reconnection pulse.

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  • 6.
    Aikio, Anita T.
    et al.
    Oulu, Finland.
    Pitkänen, Timo
    Oulu, Finland.
    Honkonen, Ilja
    Helsinki, Finland.
    Palmroth, Minna
    Helsinki, Finland.
    Amm, Olaf
    Helsinki, Finland.
    IMF effect on the polar cap contraction and expansion during a period of substorms2013In: Annales Geophysicae, ISSN 0992-7689, E-ISSN 1432-0576, Vol. 31, p. 1021-1034Article in journal (Refereed)
    Abstract [en]

    The polar cap boundary (PCB) location and motion in the nightside ionosphere has been studied by using measurements from the EISCAT radars and the MIRACLE magnetometers during a period of four substorms on 18 February 2004. The OMNI database has been used for observations of the solar wind and the Geotail satellite for magnetospheric measurements. In addition, the event was modelled by the GUMICS-4 MHD simulation. The simulation of the PCB location was in a rather good agreement with the experimental estimates at the EISCAT longitude. During the first three substorm expansion phases, neither the local observations nor the global simulation showed any poleward motions of the PCB, even though the electrojets intensified. Rapid poleward motions of the PCB took place only in the early recovery phases of the substorms. Hence, in these cases the nightside reconnection rate was locally higher in the recovery phase than in the expansion phase.

    In addition, we suggest that the IMF Bz component correlated with the nightside tail inclination angle and the PCB location with about a 17-min delay from the bow shock. By taking the delay into account, the IMF northward turnings were associated with dipolarizations of the magnetotail and poleward motions of the PCB in the recovery phase. The mechanism behind this effect should be studied further.

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  • 7. Aikio, Anita T.
    et al.
    Pitkänen, Timo
    Honkonen, Ilja
    Palmroth, Minna
    Amm, Olaf
    IMF effect on the polar cap contraction and expansion during a period of substorms2013In: Annales Geophysicae, ISSN 0992-7689, E-ISSN 1432-0576, Vol. 31, p. 1021-1034Article in journal (Refereed)
  • 8. Aikio, Anita T.
    et al.
    Pitkänen, Timo
    Kozlovsky, Alexander
    Amm, Olaf
    Method to locate the polar cap boundary in the nightside ionosphere and application to a substorm event2006In: Annales Geophysicae, ISSN 0992-7689, E-ISSN 1432-0576, Vol. 24, p. 1905-1917Article in journal (Refereed)
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  • 9.
    Aizawa, S.
    et al.
    IRAP, CNRS-CNES-UPS, Toulouse, France; Graduate School of Science, Tohoku University, Sendai, Japan.
    Griton, L.S.
    IRAP, CNRS-CNES-UPS, Toulouse, France; LESIA, Observatoire de Paris, Université PSL, CNRS, Sorbonne Université, Université de Paris, 5 place Jules Janssen, Meudon, France.
    Fatemi, Shahab
    Umeå University, Faculty of Science and Technology, Department of Physics. Swedish Institute of Space Physics, Kiruna, Sweden.
    Exner, W.
    Institute for Geophysics and Extraterrestrial Physics, Technische Universität Braunschweig, Braunschweig, Germany; Institute for Theoretical Physics, Technische Universität Braunschweig, Braunschweig, Germany; School of Earth and Atmospheric Sciences, Georgia Institute of Technology, Atlanta, United States.
    Deca, J.
    Laboratory for Atmospheric and Space Physics (LASP), University of Colorado Boulder, CO, Boulder, United States; Institute for Modeling Plasma, Atmospheres and Cosmic Dust, NASA/SSERVI, CA, United States; Laboratoire Atmosphères, Milieux, Observations Spatiales (LATMOS), Université de Versailles à Saint Quentin, Guyancourt, France.
    Pantellini, F.
    LESIA, Observatoire de Paris, Université PSL, CNRS, Sorbonne Université, Université de Paris, 5 place Jules Janssen, Meudon, France.
    Yagi, M.
    RIKEN, Kobe, Japan.
    Heyner, D.
    Institute for Geophysics and Extraterrestrial Physics, Technische Universität Braunschweig, Braunschweig, Germany.
    Génot, V.
    IRAP, CNRS-CNES-UPS, Toulouse, France.
    André, N.
    IRAP, CNRS-CNES-UPS, Toulouse, France.
    Amaya, J.
    CmPA, Mathematics Department, KU Leuven, Belgium.
    Murakami, G.
    ISAS/JAXA, Sagamihara, Japan.
    Beigbeder, L.
    GFI, Toulouse, France.
    Gangloff, M.
    IRAP, CNRS-CNES-UPS, Toulouse, France.
    Bouchemit, M.
    IRAP, CNRS-CNES-UPS, Toulouse, France.
    Budnik, E.
    Noveltis, Toulouse, France.
    Usui, H.
    Kobe University, Kobe, Japan.
    Cross-comparison of global simulation models applied to Mercury's dayside magnetosphere2021In: Planetary and Space Science, ISSN 0032-0633, E-ISSN 1873-5088, Vol. 198, article id 105176Article in journal (Refereed)
    Abstract [en]

    We present the first comparison of multiple global simulations of the solar wind interaction with Mercury's dayside magnetosphere, conducted in the framework of the international collaborative project SHOTS - Studies on Hermean magnetosphere Oriented Theories and Simulations. Two 3D magnetohydrodynamic and two 3D hybrid simulation codes are used to investigate the global response of the Hermean magnetosphere without its exosphere to a northward-oriented interplanetary magnetic field. We cross-compare the results of the four codes for a theoretical case and a MESSENGER orbit with similar upstream plasma conditions. The models agree on bowshock and magnetopause locations at 2.1 ​± ​0.11 and 1.4 ​± ​0.1 Mercury planetary radii, respectively. The latter locations may be influenced by subtle differences in the treatment of the plasma boundary at the planetary surface. The predicted magnetosheath thickness varies less between the codes. Finally, we also sample the plasma data along virtual trajectories of BepiColombo's Magnetospheric and Planetary Orbiter. Our ability to accurately predict the structure of the Hermean magnetosphere aids the analysis of the onboard plasma measurements of past and future magnetospheric missions.

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  • 10. Ali, S
    et al.
    Moslem, WM
    Shukla, Padma Kant
    Umeå University, Faculty of Science and Technology, Department of Physics. 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; 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.
    Wake potential with mobile positive/negative ions in multicomponent dusty plasmas2008In: Physics Letters A, ISSN 0375-9601, E-ISSN 1873-2429, Vol. 372, no 44, p. 6650-6652Article in journal (Refereed)
    Abstract [en]

    We employ the test charge approach to calculate the electrostatic potential for a test charge in a multicomponent dusty plasma, whose constituents are the Boltzmann distributed electrons, mobile positive and negative ions, and immobile positive/negative charged dust particles. By using the modified dielectric constant of the dust-ion-acoustic (DIA) waves, the Debye screening and wake potentials are obtained. It is found that the presence of mobile negative ions significantly modify the DIA speed and the wake potential. The present results are relevant to polar mesosphere and microelectronic in the context of charged particle attraction and repulsion.

  • 11. Ali, S
    et al.
    Shukla, Padma K
    Umeå University, Faculty of Science and Technology, Department of Physics. 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 plasma2006In: Physics of Plasmas, ISSN 1070-664X, E-ISSN 1089-7674, Vol. 13, no 2, article id 022313Article in journal (Refereed)
    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.

  • 12. Ali, S
    et al.
    Shukla, Padma Kant
    Umeå University, Faculty of Science and Technology, Department of Physics. 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 magnetoplasmas2006In: Physics of Plasmas, ISSN 1070-664X, E-ISSN 1089-7674, Vol. 13, no 5, article id 052113Article in journal (Refereed)
    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.

  • 13.
    Ali, Shahid
    Umeå University, Faculty of Science and Technology, Physics.
    Waves and instabilities in quantum plasmas2008Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    The study of waves and instabilities in quantum plasmas is of fundamental importance for understanding collective interactions in superdense astrophysical objects, in high intense laser-plasma/solid-matter interactions, in microelectronic devices and metallic nanostructures. In dense quantum plasmas, there are new pressure laws associated with the Fermi-Dirac distribution functions and new quantum forces associated with the quantum Bohm potential and the Bohr magnetization involving electron ½ spin. These forces significantly alter the collective behavior of dense quantum plasmas. This thesis contains six papers, considering several novel collective modes and instabilities at quantum scales. In Paper I, we have used the quantum hydrodynamical (QHD) model for studying the one-dimensional dust-acoustic (DA) waves incorporating the Fermi pressure law and the quantum Bohm potential. The latter modifies the DA wave dispersion relation in a collisional plasma. In Paper II, we have calculated the electrostatic potential of a test charge in an unmagnetized electron-ion quantum plasma. It is found that the Debye-Hückel and oscillatory wake potentials strongly depend upon the Fermi energy at quantum scales. The results can be of interest for explaining the charged particle attraction and repulsion in degenerate quantum plasmas, such as those in semiconductor and microelectronic devices. Paper III presents the parametric study of nonlinear electrostatic waves in two-dimensional collisionless quantum dusty plasmas. A reductive perturbation method has been employed to the QHD equations together with the Poisson equation, obtaining the cylindrical Kadomtsev-Petviashvili (CKP) equations and their stationary localized solutions. We have numerically examined the quantum mechanical and geometrical effects on the profiles of nonplanar quantum dust-ion-acoustic (DIA) and DA solitary waves. The role of static as well as mobile (negatively or positively charged) dust particles on the low-frequency electrostatic waves has also been highlighted for metallic nanostructures. Paper IV introduces the nonlinear properties of the ion-sound waves in a dense electron-ion Fermi magnetoplasma. The computational analysis of the nonlinear system reveals that the Sagdeev-like potential and the ion-sound density excitations are significantly affected by the wave direction cosine and the Mach number at quantum scales. Paper V considers the nonlinear interactions of electrostatic upper-hybrid (UH), ion-cyclotron (IC), lower-hybrid (LH), and Alfvén waves in a quantum magnetoplasma. The nonlinear dispersion relations have been analyzed analytically to obtain the growth rates for both the decay and modulational instabilities involving the dispersive IC, LH, and Alfvén waves. In Paper VI, we have identified a new drift-like dissipative instability in a collisional quantum plasma. The modified unstable drift-like mode can cause cross-field anomalous ion-diffusion at quantum scales.

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  • 14.
    Al-Naseri, Haidar
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Modelling and analyzing strong-field effects in quantum plasma2023Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Under the extreme conditions that can be found around dense stars and in the accretion discs of black holes, several strong-field quantum phenomena dominate the dynamics of the plasma. This includes the creation of matter and anti-matter from the vacuum (Schwinger mechanism), radiation reaction and Landau quantization. Some of these strong field phenomena were presented theoretically a century ago but have never been verified in experiments due to the difficulty of creating the required extreme conditions in the lab. However, with the development of laser facilities in the past decades, it will be possible to observe several extreme physical phenomena in the near future. To conduct experiments on these extreme phenomena, theoretical simulations need to be constructed as a guide for optimizing experiments.

    This thesis is concerned with developing and analyzing strong field phenomena in kinetic plasma models. The focus is to extend current kinetic models to include several physical phenomena that are relevant to future experiments on laser-plasma interaction. In particular, a kinetic theory based on the Wigner transformation of the Dirac equation has been analyzed in different regimes. This kinetic model is used to study the plasma dynamics at the Schwinger limit, where collective plasma effects and several quantum processes are studied.

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  • 15.
    Al-Naseri, Haidar
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Quantum kinetic relativistic theory of linearized waves in magnetized plasmas2018Independent thesis Advanced level (degree of Master (One Year)), 10 credits / 15 HE creditsStudent thesis
    Abstract [en]

    In this work we have studied linear wave propagation in magnetized plasmas using a fully relativistic kinetic equation of spin-1/2 particles in the long scale approximation. The linearized kinetic equation is very long and complicated, hence we worked with restricted geometries in order to simplify the calculations. The dispersion relation of the relativistic model was calculated and compared with a dispersion relation from a previous work at the semi-relativistic limit.

    Moreover, a new mode was discovered that survives in the zero temperature limit. The origin of the mode in the kinetic equation was discussed and derived from a non-relativistic kinetic equation from a previous work.

  • 16.
    Al-Naseri, Haidar
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Brodin, Gert
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Applicability of the Klein-Gordon equation for pair production in vacuum and plasma2023In: Physical review. E, ISSN 2470-0045, E-ISSN 2470-0053, Vol. 108, no 5, article id 055205Article in journal (Refereed)
    Abstract [en]

    In this paper, a phase-space description of electron-positron pair-creation will be applied, based on a Wigner transformation of the Klein-Gordon equation. The resulting theory is similar in many respects to the equations from the Dirac-Heisenberg-Wigner formalism. However, in the former case, all physics related to particle spin is neglected. In the present paper we compare the pair-production rate in vacuum and plasmas, with and without spin effects, in order to evaluate the accuracy and applicability of the spinless approximation. It is found that for modest frequencies of the electromagnetic field, the pair production rate of the Klein-Gordon theory is a good approximation to the Dirac theory, provided the matter density is small enough for Pauli blocking to be neglected, and a factor of two related to the difference in the vacuum energy density is compensated for.  

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  • 17.
    Al-Naseri, Haidar
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Brodin, Gert
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Linear pair-creation damping of high-frequency plasma oscillation2022In: Physics of Plasmas, ISSN 1070-664X, E-ISSN 1089-7674, Vol. 29, no 4, article id 042106Article in journal (Refereed)
    Abstract [en]

    We have studied the linear dispersion relation for Langmuir waves in plasmas of very high density, based on the Dirac-Heisenberg-Wigner formalism. The vacuum contribution to the physical observables leads to ultraviolet divergences, which are removed by a charge renormalization. The remaining vacuum contribution is small and is in agreement with previously derived expressions for the time-dependent vacuum polarization. The main new feature of the theory is a damping mechanism similar to Landau damping, but where the plasmon energy gives rise to creation of electron-positron pairs. The dependence of the damping rate (pair-creation rate) on the wavenumber, temperature, and density is analyzed. Finally, the analytical results of linearized theory are compared with numerical solutions.

  • 18.
    Al-Naseri, Haidar
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Brodin, Gert
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Ponderomotive force due to the intrinsic spin for electrostatic waves in a magnetized plasma2023In: Physics of Plasmas, ISSN 1070-664X, E-ISSN 1089-7674, Vol. 30, no 6, article id 062109Article in journal (Refereed)
    Abstract [en]

    We study the contribution from the electron spin to the ponderomotive force, using a quantum kinetic model, including the spin-orbit correction. Specifically, we derive an analytical expression for the ponderomotive force, applicable for electrostatic waves propagating parallel to an external magnetic field. To evaluate the expression, we focus on the case of Langmuir waves and on the case of the spin resonance wave mode, where the classical and spin contributions to the ponderomotive force are compared. Somewhat surprisingly, depending on the parameter regime, we find that the spin contribution to the ponderomotive force may dominate for the Langmuir wave, whereas the classical contribution can dominate for the spin resonance mode.

  • 19.
    Al-Naseri, Haidar
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Brodin, Gert
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Radiation reaction effects in relativistic plasmas: the electrostatic limit2023In: Physical review. E, ISSN 2470-0045, E-ISSN 2470-0053, Vol. 107, no 3, article id 035203Article in journal (Refereed)
    Abstract [en]

    We study the evolution of electrostatic plasma waves, using the relativistic Vlasov equation extended by the Landau-Lifshitz radiation reaction, accounting for the back-reaction due to the emission of single particle Larmor radiation. In particular, the Langmuir wave damping is calculated as a function of wave number, initial temperature, and initial electric field amplitude. Moreover, the background distribution function loses energy in the process, and we calculate the cooling rate as a function of initial temperature and initial wave amplitude. Finally, we investigate how the relative magnitude of wave damping and background cooling varies with the initial parameters. In particular, it is found that the relative contribution to the energy loss associated with background cooling decreases slowly with the initial wave amplitude.

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  • 20.
    Al-Naseri, Haidar
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Zamanian, Jens
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Brodin, Gert
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Plasma dynamics and vacuum pair creation using the Dirac-Heisenberg-Wigner formalism2021In: Physical review. E, ISSN 2470-0045, E-ISSN 2470-0053, Vol. 104, no 1, article id 015207Article in journal (Refereed)
    Abstract [en]

    We derive a system of coupled partial differential equations for the equal-time Wigner function in an arbitrary strong electromagnetic field using the Dirac-Heisenberg-Wigner formalism. In the electrostatic limit, we present a system of four coupled partial differential equations, which are completed by Ampères law. This electrostatic system is further studied for two different cases. In the first case, we consider linearized wave propagation in a plasma accounting for the nonzero vacuum expectation values. We then derive the dispersion relation and compare it with well-known limiting cases. In the second case, we consider Schwinger pair production using the local density approximation to allow for analytical treatment. The dependence of the pair production rate on the perpendicular momentum is investigated and it turns out that the spread of the produced pairs along with perpendicular momentum depends on the strength of the applied electric field.

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  • 21.
    Al-Naseri, Haidar
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Zamanian, Jens
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Ekman, Robin
    Brodin, Gert
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Kinetic theory for spin-1/2 particles in ultrastrong magnetic fields2020In: Physical Review E. Statistical, Nonlinear, and Soft Matter Physics, ISSN 1539-3755, E-ISSN 1550-2376, Vol. 102, no 4, article id 043203Article in journal (Refereed)
    Abstract [en]

    When the Zecman energy approaches the characteristic kinetic energy of electrons, Landau quantization becomes important. In the vicinity of magnetars, the Zeeman energy can even be relativistic. We start from the Dirac equation and derive a kinetic equation for electrons, focusing on the phenomenon of Landau quantization in such ultrastrong but constant magnetic fields, neglecting short-scale quantum phenomena. It turns out that the usual relativistic gamma factor of the Vlasov equation is replaced by an energy operator, depending on the spin state, and also containing momentum derivatives. Furthermore, we show that the energy eigenstates in a magnetic field can be computed as eigenfunctions of this operator. The dispersion relation for electrostatic waves in a plasma is computed, and the significance of our results is discussed.

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  • 22.
    Arvelius, Johan
    Umeå University, Faculty of Science and Technology, Space Science.
    Calibration and quality assessment of DESCARTES: grabsampler for stratospheric tracers2005Doctoral thesis, monograph (Other academic)
    Abstract [en]

    DESCARTES is a light-weight, balloon-borne grab sampler for stratospheric long-lived tracers developed at the University of Cambridge. 33 flights have been performed with two versions of the instrument at northern latitudes by the DESCARTES team at the Swedish Institute of Space Physics (IRF) in Kiruna during the years 1997-2000.

    The general interest in long-lived stratospheric tracers is to study the general global circulation of air in the stratosphere and the exchange between the stratosphere and troposphere. In the study of chemical ozone depletion in the stratosphere, long-lived tracers serve as an important reference to distinguish between the variations in ozone of dynamical and chemical origin.

    This thesis focuses on calibrations and quality assessment of the measurements made with the third version of the DESCARTES instrument based at IRF. Two different general approaches to make calibrations are discussed. Uncertainty estimations for both of these methods are made and the results are tested by laboratory methods and by comparisons to other instruments, including comparisons between two versions of DESCARTES. Analyzed and calibrated flight data for all successful flights are presented.

    The basic principle of the instrument is to chemically adsorb a number of tracers (in practice only CFC-11 is measured) in an adsorption bed of Carboxen in a micro trap through which the sampled air is driven by a pump. After recovery the adsorbed species in the trap is desorbed by electrical heating of the trap and analysed by gas chromatography.

    The resulting estimated mixing ratios from the instrument are directly dependent on the adsorption of the sampled species being quantitative in the traps. Laboratory experiments are described using two traps in series, where the performance of the first is tested by sampling the breakthrough by the second. A model is developed to recreate these tests in order to be able to compensate for breakthrough during flights. The model showed that the adsorption in the traps is not explained by simple chromatographic theory and the results allow us only to give an estimation of the uncertainty due to breakthrough.

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  • 23.
    Arvelius, S.
    et al.
    Umeå University, Faculty of Science and Technology, Space Science.
    Yamauchi, M.
    Nilsson, H.
    Lundin, R.
    Hobara, Y.
    Rème, H.
    Bavassano- Cattaneo, M. B.
    Paschmann, G.
    Korth, A.
    Kistler, L. M.
    Parks, G. K.
    Statistical study of relationships between dayside high-altitude and high-latitude O+ ion outflows, solar winds, and geomagnetic activity2005In: Annales Geophysicae, ISSN 0992-7689, E-ISSN 1432-0576, Vol. 23, p. 1909-1916Article in journal (Refereed)
    Abstract [en]

    The persistent outflows of O+ ions observed by the Cluster CIS/CODIF instrument were studied statistically in the high-altitude (from 3 up to 11 RE) and high-latitude (from 70 to ~90 deg invariant latitude, ILAT) polar region. The principal results are: (1) Outflowing O+ ions with more than 1keV are observed above 10 RE geocentric distance and above 85deg ILAT location; (2) at 6-8 RE geocentric distance, the latitudinal distribution of O+ ion outflow is consistent with velocity filter dispersion from a source equatorward and below the spacecraft (e.g. the cusp/cleft); (3) however, at 8-12 RE geocentric distance the distribution of O+ outflows cannot be explained by velocity filter only. The results suggest that additional energization or acceleration processes for outflowing O+ ions occur at high altitudes and high latitudes in the dayside polar region.

  • 24.
    Arvelius, Sachiko
    Umeå University, Faculty of Science and Technology, Space Science.
    Energization and Acceleration of Dayside Polar Outflowing Oxygen2005Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    This thesis deals with energetic oxygen ions (i.e. single-charged atomic oxygen ions, O+) at altitudes higher than 5 Earth radii (RE) and at latitudes above 75 (toward 90) degrees invariant latitude (deg ILAT) in the dayside polar magnetosphere observed by Cluster. The instrument used in this study is CIS (Cluster Ion Spectrometry experiment) / CODIF (a time-of-flight ion COmposition and DIstribution Function analyser), which covers an energy range from »10 eV up to 38 keV. Cluster detected O+ with energies more than 1 keV (hereafter termed “keV O+”), indicating that energization and/or acceleration process(es) take place in the dayside high-altitude (inside magnetopause) and high-latitude region. These O+ are outflowing (precisely, upward-going along the geomagnetic field lines), and these outflowing keV O+ show a heated (or energized) signature in the velocity distribution as well.

    First, outflowing O+ are observed at the poleward cusp and/or the mantle formed a partial shell-like configuration seen in the velocity distribution. Second, the latitudinal distribution of outflowing O+ (most of them have energies less than 1 keV statistically) observed below 7 RE is consistent with velocity filter effect by the polar convection, while the latitudinal distribution of outflowing keV O+ observed above 7 RE cannot be explained by velocity filter effect only, i.e. this indicates that additional energization and/or acceleration takes place at higher altitudes in the dayside polar region. Thirdly, a tendency to observe outflowing keV O+ for during different geomagnetic conditions is studied. The keV O+ above 9 RE is more often for K p¸5 rather than for K p•3. However the energy of O+ is not dependent on ASY /SYM indices.

    Finally, the dependence on the solar wind conditions is also studied. The energization and/or acceleration of outflowing O+ is controlled by both solar wind moments (except solar wind electric field) and strong southward interplanetary magnetic field (IMF) at the time scale of tens of minutes at only higher altitudes. Further examination shows that solar wind dependence is different at three regions: one is the poleward cusp, another is the low-altitude polar cap, and finally the high-altitude polar cap, combining all the results. There is (a) new energization and/or acceleration process(es) at the high-altitude polar cap. On the other hand, flux enhancement of O+ observed above 5 RE is also controlled by solar wind moments (e.g. solar wind electric field) and strong southward IMF, however the ionospheric changes play a more important role on the flux enhancement of O+.

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  • 25.
    Asenjo, Felipe A.
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Zamanian, Jens
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Marklund, Mattias
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Brodin, Gert
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Johansson, Petter
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Semi-relativistic effects in spin-1/2 quantum plasmas2012In: New Journal of Physics, E-ISSN 1367-2630, Vol. 14, p. 073042-Article in journal (Refereed)
    Abstract [en]

    Emerging possibilities for creating and studying novel plasma regimes, e. g. relativistic plasmas and dense systems, in a controlled laboratory environment also require new modeling tools for such systems. This motivates theoretical studies of the kinetic theory governing the dynamics of plasmas for which both relativistic and quantum effects occur simultaneously. Here, we investigate relativistic corrections to the Pauli Hamiltonian in the context of a scalar kinetic theory for spin-1/2 quantum plasmas. In particular, we formulate a quantum kinetic theory for the collective motion of electrons that takes into account effects such as spin-orbit coupling and Zitterbewegung. We discuss the implications and possible applications of our findings.

  • 26.
    Ayllon, Rolando
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Cyclotron Damping in Magnetized Plasmas2014Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    The aim of this thesis was to study the cyclotron damping in magnetized plasmas using a different approach to the dielectric tensor that is the stardard way to study this case. In this approach given we deduce a set of coupled differential equations that give us the evolution of the electric field and the distribution function. The system of coupled equations can not be solved analitically, that is why we have found numerical solutions. The algorithm we used to obtain the numerical solutions is the staggered leap-frog method that common used in problems involving electromagnetic fields.

    We have studied two cases where we consider two different initial conditions for our distribution function in the velocity space. In the first example we used ˜g(t = 0, v_n) = 0. In this case we found that the electric field decays exponentially and there is phase mixing in the evolution of the distribution function. As second example we used as initial condition the expression ˜g(t = 0, v_n) = E_n/(iv_n −\gamma). In this case the phase mixing is less pronounced compared to the first example, and the electric field start growing until the oscillations of the distribution function start to become important, then the electric field start to decay slowly.

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  • 27.
    Azimi, Mohammad
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Study of the linear and nonlinear damping in plasma via simulation2019Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
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  • 28.
    Backman, Fredrick
    Umeå University, Faculty of Arts, Department of historical, philosophical and religious studies.
    Från föhn till feu!: Esrange och den norrländska rymdverksamhetens tillkomsthistoria från sekelskiftet 1900 till 19662010Independent thesis Advanced level (degree of Master (One Year)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    This essay is about the origin, planning and establishment of the European Space Research Organisation's (ESRO) sounding rocket base Esrange outside Kiruna in Northern Sweden. Three main questions are examined. First I show there were not just scientific and technical but also political, economical as well as military reasons to build a European rocket base. Second, I scrutinize the reasons to choose Northern Sweden as the location for the rocket base. As it turns out, the main reasons were the favourable location of Northern Sweden within the aurora oval zone, the proximity of the Kiruna Geophysical Observatory, and the possibility to use a large, although not quite uninhabited, area where the launched rockets could crash. Finally, I examine the difficulty of talking about boundaries of various kinds, such as temporal, spatial and functional. The essay also provides a discussion on possible ways to continue research on this topic.

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  • 29. Baikov, I. V.
    et al.
    Suslin, V. M.
    Chechetkin, V. M.
    Bychkov, V
    Umeå University, Faculty of Science and Technology, Physics.
    Stenflo, Lennart
    Umeå University, Faculty of Science and Technology, Physics.
    Radiation of a neutrino mechanism for type II supernovae2007In: Astronomy Reports, Vol. 51, p. 274-Article in journal (Refereed)
  • 30. Bains, AS
    et al.
    Misra, Amar P
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Saini, NS
    Gill, TS
    Modulational instability of ion-acoustic wave envelopes in magnetized quantum electron-positron-ion plasmas2010In: Physics of Plasmas, ISSN 1070-664X, E-ISSN 1089-7674, Vol. 17, no 1, article id 012103Article in journal (Refereed)
    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.

  • 31.
    Bakırcıoğlu, Doğukan
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Dirac Heisenberg Wigner Formalism on Plasma Physics2021Independent thesis Basic level (degree of Bachelor), 10 credits / 15 HE creditsStudent thesis
    Abstract [en]

    Aim of this paper is studying classical limits for quantum plasma systems. For this reason we have  first studied the Vlasov model used to describe for classical plasma. After that we have considered the Wignerfunction for modelling quantum plasmas and we have shown its classical limit. Next, we wanted to generalize our discussion to the quantum relativistic case and also add the fermionic nature of the electrons hence, we have used the DHW(Dirac-Heisenberg-Wigner) formalism which was created by Bialynicki-Birula, Gornicki, and Rafelski in 1991. We have shown how the DHW formalism reduces to the Vlasov model in the classical limit.

  • 32. Banerjee, S
    et al.
    Misra, Amar P
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Shukla, P K
    Rondoni, L
    Spatiotemporal chaos and the dynamics of coupled Langmuir and ion-acoustic waves in plasmas2010In: Physical Review E. Statistical, Nonlinear, and Soft Matter Physics, ISSN 1539-3755, E-ISSN 1550-2376, Vol. 81, no 4, article id 046405Article in journal (Refereed)
    Abstract [en]

    A simulation study is performed to investigate the dynamics of coupled Langmuir waves (LWs) and ion-acoustic waves (IAWs) in an unmagnetized plasma. The effects of dispersion due to charge separation and the density nonlinearity associated with the IAWs are considered to modify the properties of Langmuir solitons, as well as to model the dynamics of relatively large amplitude wave envelopes. It is found that the Langmuir wave electric field, indeed, increases by the effect of ion-wave nonlinearity (IWN). Use of a low-dimensional model, based on three Fourier modes, shows that a transition to temporal chaos is possible, when the length scale of the linearly excited modes is larger than that of the most unstable ones. The chaotic behaviors of the unstable modes are identified by the analysis of Lyapunov exponent spectra. The space-time evolution of the coupled LWs and IAWs shows that the IWN can cause the excitation of many unstable harmonic modes and can lead to strong IAW emission. This occurs when the initial wave field is relatively large or the length scale of IAWs is larger than the soliton characteristic size. Numerical simulation also reveals that many solitary patterns can be excited and generated through the modulational instability of unstable harmonic modes. As time goes on, these solitons are seen to appear in the spatially partial coherence state due to the free ion-acoustic radiation as well as in the state of spatiotemporal chaos due to collision and fusion in the stochastic motion. The latter results in the redistribution of initial wave energy into a few modes with small length scales, which may lead to the onset of Langmuir turbulence in laboratory as well as space plasmas.

  • 33.
    Behar, Etienne
    et al.
    Solar System Physics And Space Technology, Swedish Institute Of Space Physics, Kiruna, Sweden; Laboratoire Lagrange, Observatoire De La Côte d'Azur, Université Côte d'Azur, Cnrs, Nice, France.
    Fatemi, Shahab
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Henri, Pierre
    Laboratoire Lagrange, Observatoire De La Côte d'Azur, Université Côte d'Azur, Cnrs, Nice, France; LPC2E, Orléans, France.
    Holmström, Mats
    Laboratoire Lagrange, Observatoire De La Côte d'Azur, Université Côte d'Azur, Cnrs, Nice, France.
    Menura: A code for simulating the interaction between a turbulent solar wind and solar system bodies2022In: Annales Geophysicae, ISSN 0992-7689, E-ISSN 1432-0576, Vol. 40, no 3, p. 281-297Article in journal (Refereed)
    Abstract [en]

    Despite the close relationship between planetary science and plasma physics, few advanced numerical tools allow bridging the two topics. The code Menura proposes a breakthrough towards the self-consistent modelling of these overlapping fields, in a novel two-step approach allowing for the global simulation of the interaction between a fully turbulent solar wind and various bodies of the solar system. This article introduces the new code and its two-step global algorithm, illustrated by a first example: the interaction between a turbulent solar wind and a comet.

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  • 34.
    Behar, Etienne
    et al.
    Swedish Institute of Space Physics, Kiruna.
    Lindkvist, Jesper
    Umeå University, Faculty of Science and Technology, Department of Physics. Swedish Institute of Space Physics, Kiruna.
    Nilsson, Hans
    Swedish Institute of Space Physics, Kiruna.
    Holmström, Mats
    Swedish Institute of Space Physics, Kiruna.
    Stenberg-Wieser, Gabriella
    Swedish Institute of Space Physics, Kiruna.
    Ramstad, Robin
    Umeå University, Faculty of Science and Technology, Department of Physics. Swedish Institute of Space Physics, Kiruna.
    Götz, Charlotte
    Technicsche Universität Braunschweig, Institute for Geophysics an Extraterrestrial Physics, Braunschweig.
    Mass-loading of the solar wind at 67P/Churyumov-Gerasimenko: Observations and modelling2016In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 596, article id A42Article in journal (Refereed)
    Abstract [en]

    Context. The first long-term in-situ observation of the plasma environment in the vicinity of a comet, as provided by the European Rosetta spacecraft.

    Aims. Here we offer characterisation of the solar wind flow near 67P/Churyumov-Gerasimenko (67P) and its long term evolution during low nucleus activity. We also aim to quantify and interpret the deflection and deceleration of the flow expected from ionization of neutral cometary particles within the undisturbed solar wind.

    Methods. We have analysed in situ ion and magnetic field data and combined this with hybrid modeling of the interaction between the solar wind and the comet atmosphere.

    Results. The solar wind deflection is increasing with decreasing heliocentric distances, and exhibits very little deceleration. This is seen both in observations and in modeled solar wind protons. According to our model, energy and momentum are transferred from the solar wind to the coma in a single region, centered on the nucleus, with a size in the order of 1000 km. This interaction affects, over larger scales, the downstream modeled solar wind flow. The energy gained by the cometary ions is a small fraction of the energy available in the solar wind.

    Conclusions. The deflection of the solar wind is the strongest and clearest signature of the mass-loading for a small, low-activity comet, whereas there is little deceleration of the solar wind. 

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  • 35.
    Belova, Alla
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Kirkwood, Sheila
    Murtagh, Donal
    Planetary waves in ozone and temperature in the Northern hemisphere winter of 2002-2003 by Odin satellite data2009In: Annales Geophysicae, ISSN 0992-7689, E-ISSN 1432-0576, Vol. 27, p. 1189-1206Article in journal (Refereed)
    Abstract [en]

    Temperature and ozone data from the sub-millimetre radiometer (SMR) installed aboard the Odin satellite have been examined to study the relationship between temperature and ozone concentration in the lower and upper stratosphere in winter time. The retrieved ozone and temperature profiles have been considered between the range of 24–46 km during the Northern Hemisphere (NH) winter of December 2002 to March 2003 and January to March 2005. A comparison between the ozone mixing ratio and temperature fields has been made for the zonal means, wavenumber one variations and 5-day planetary waves. The amplitude values in temperature variations are ~5 K in the wavenumber one and 0.5–1 K in the 5-day wave. In ozone mixing ratio, the amplitudes reach ~0.5 ppmv in the wavenumber one and 0.05–0.1 ppmv in the 5-day wave.

    Several stratospheric warming events were observed during the NH winters of 2002/2003 and early 2005. Along with these warming events, amplification of the amplitude has been detected in wavenumber one (up to 30 K in temperature and 1.25 ppmv in ozone) and partly in the 5-day perturbation (up to 2 K in temperature and 0.2 ppmv in ozone). 

    In general, the results show the expected in-phase behavior between the temperature and ozone fields in the lower stratosphere due to dynamic effects, and an out-of-phase pattern in the upper stratosphere, which is expected as a result of photochemical effects. However, these relationships are not valid for zonal means and wavenumber one components when the wave amplitudes are changing dramatically during the strongest stratospheric warming event (at the end of December 2002/beginning of January 2003). Also, for several shorter intervals, the 5-day perturbations in ozone and temperature are not well-correlated at lower heights, particularly when conditions change rapidly. 

    Odin's basic observation schedule provides stratosphere mode data every third day and to validate the reliability of the 5-day waves extracted from the Odin measurements, additional independent data have been analysed in this study: temperature assimilation data by the European Centre for Medium-range Weather Forecasts (ECMWF) for the NH winter of 2002/2003, and satellite measurements of temperature and ozone by the Microwave Limb Sounder (MLS) on board the Aura satellite for the NH winter in early 2005. 

    Good agreement between the temperature fields from Odin and ECMWF data is found at middle latitude where, in general, the 5-day perturbations from the two data sets coincide in both phase and amplitude throughout the examined interval. Analysis of the wavenumber one and the 5-day wave perturbations in temperature and ozone fields from Odin and from Aura demonstrates that, for the largest part of the examined period, quite similar characteristics are found in the spatial and temporal domain, with slightly larger amplitude values seen by Aura. Hence, the comparison between the Odin data, sampled each third day, and daily data from Aura and the ECMWF shows that the Odin data are sufficiently reliable to estimate the properties of the 5-day oscillations, at least for the locations and time intervals with strong wave activity.

  • 36.
    Belova, Alla
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Kirkwood, Sheila
    Murtagh, Donal
    Singer, Werner
    Hocking, Wayne
    Mitchell, Nick
    Five-day planetary waves in the middle atmosphere from Odin satellite data and ground-based instruments in Northern Hemisphere summer 2003, 2004, 2005 and 20072008In: Annales Geophysicae, ISSN 0992-7689, E-ISSN 1432-0576, Vol. 26, p. 3557-3570Article in journal (Refereed)
    Abstract [en]

    A number of studies have shown that 5-day planetary waves modulate noctilucent clouds and the closely related Polar Mesosphere Summer Echoes (PMSE) at the summer mesopause. Summer stratospheric winds should inhibit wave propagation through the stratosphere and, although some numerical models (Geisler and Dickinson, 1976) do show a possibility for upward wave propagation, it has also been suggested that the upward propagation may in practice be confined to the winter hemisphere with horizontal propagation of the wave from the winter to the summer hemisphere at mesosphere heights causing the effects observed at the summer mesopause. It has further been proposed (Garcia et al., 2005) that 5-day planetary waves observed in the summer mesosphere could be excited in-situ by baroclinic instability in the upper mesosphere. In this study, we first extract and analyze 5-day planetary wave characteristics on a global scale in the middle atmosphere (up to 54 km in temperature, and up to 68 km in ozone concentration) using measurements by the Odin satellite for selected days during northern hemisphere summer from 2003, 2004, 2005 and 2007. Second, we show that 5-day temperature fluctuations consistent with westward-traveling 5-day waves are present at the summer mesopause, using local ground-based meteor-radar observations. Finally we examine whether any of three possible sources of the detected temperature fluctuations at the summer mesopause can be excluded: upward propagation from the stratosphere in the summer-hemisphere, horizontal propagation from the winter-hemisphere or in-situ excitation as a result of the baroclinic instability. We find that in one case, far from solstice, the baroclinic instability is unlikely to be involved. In one further case, close to solstice, upward propagation in the same hemisphere seems to be ruled out. In all other cases, all or any of the three proposed mechanisms are consistent with the observations.

  • 37.
    Bergman, Sofia
    Umeå University, Faculty of Science and Technology, Department of Physics. Swedish Institute of Space Physics, Kiruna, Sweden.
    Low-energy ions around comet 67P/Churyumov-Gerasimenko2021Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Low-energy ions play important roles in the formation of the plasma environment around a comet. Reliable ways of measuring these ions are therefore of high importance to fully understand the processes and dynamics of this environment. Unfortunately, low-energy ions are infamously difficult to detect. A spacecraft interacts with the surrounding environment, which leads to an accumulation of charge on the spacecraft surface. As a result, the surface acquires an electrostatic potential with respect to the surrounding plasma, which can be either positive or negative. Low-energy ions are then attracted to or repelled from the charged surface before being detected by the instrument on board, resulting in an energy shift and change of travel direction of the ions. 

    The Rosetta mission studied comet 67P/Churyumov-Gerasimenko during the years 2014-2016, and provided the most detailed observations of a comet and its environment to date. The Ion Composition Analyzer of the Rosetta Plasma Consortium (RPC-ICA) measured positive ions in the cometary environment with energies down to just a few eV. The low-energy part of the data is, however, difficult to interpret due to the distortions caused by the spacecraft potential. 

    In this thesis, the Spacecraft Plasma Interaction Software (SPIS) is used to correct the low-energy ion measurements made by RPC-ICA for the effects introduced by the spacecraft potential. The distortion of the effective field of view is modelled for different ion energies and plasma environments, and the results are used to correct the flow direction of low-energy ions around the comet. The FOV distortion can be considered insignificant when the energy of the ions (in eV) is twice the value of the spacecraft potential (in volts). The FOV distortion at lower energies is geometry dependent, and varies substantially between different pixels of the instrument. The FOV distortion is furthermore dependent on the Debye length of the surrounding plasma. 

    The knowledge obtained from the simulations is subsequently used to study the flow direction of low-energy ions in and around the diamagnetic cavity, a region where the magnetic field is essentially zero and low-energy ions are important for the dynamics. Evidence of counter-streaming ions are found, with ions flowing both radially away from and back towards the nucleus. SPIS is also used to model the influence of the spacecraft potential on the energy spectrum of the ions, and from this the bulk speed and temperature of the low-energy ions in the diamagnetic cavity were determined to 5-10 km/s and 0.7-1.6 eV, respectively. The bulk speed is significantly above the speed of the neutral particles, indicating a weak coupling between ions and neutrals in the diamagnetic cavity.

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  • 38.
    Bergman, Sofia
    Umeå University, Faculty of Science and Technology, Department of Physics. Swedish Institute of Space Physics, Kiruna, Sweden.
    The effect of spacecraft charging on low-energy ion measurements around comet 67P/Churyumov-Gerasimenko2020Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    A spacecraft in space interacts with the surrounding environment and aqcuires an electrostatic potential. Charged particles are constantly bombarding the surface of the spacecraft, and at the same time solar EUV radiation induces photoemission, causing electrons to be emitted from the surface. The result is a transfer of charge between the environment and the spacecraft surface, and the surface charges to a positive or negative potential. The charged surface can cause interferences with scientific instruments on board. In this thesis, we investigate how spacecraft charging affects low-energy ion measurements. The Rosetta spacecraft visited comet 67P/Churyumov-Gerasimenko between the years 2014-2016. On board the spacecraft, the Ion Composition Analyzer (ICA) was measuring positive ions in the environment around the comet with the aim of investigating the interaction between cometary particles and the solar wind. Important for this interaction is ions with a low energy. Measuring these ions is, however, difficult due to the charged spacecraft surface. Rosetta was commonly charged to a negative potential, and consequently the measured positive ions were accelerated toward the surface before detection, affecting both their energy and travel direction. In this thesis, we study how the changed travel directions affected the effective field of view (FOV) of the instrument. We use the Spacecraft Plasma Interaction Software (SPIS) to simulate the spacecraft plasma interactions and the ion trajectories around the spacecraft. The results show that the FOV of ICA is severely distorted at low ion energies, but the distortion varies between different viewing directions of the instrument and is dependent on the properties of the surrounding plasma.

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  • 39.
    Bergman, Sofia
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics. Swedish Institute of Space Physics, Kiruna, Sweden.
    Stenberg Wieser, Gabriella
    Swedish Institute of Space Physics, Kiruna, Sweden.
    Wieser, Martin
    Johansson, Fredrik
    Eriksson, Anders
    The Influence of Spacecraft Charging on Low‐Energy Ion Measurements Made by RPC‐ICA on Rosetta2020In: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 125, no 1, article id e2019JA027478Article in journal (Refereed)
    Abstract [en]

    Spacecraft charging is problematic for low‐energy plasma measurements. The charged particles are attracted to or repelled from the charged spacecraft, affecting both the energy and direction of travel of the particles. The Ion Composition Analyzer (RPC‐ICA) on board the Rosetta spacecraft is suffering from this effect. RPC‐ICA was measuring positive ions in the vicinity of comet 67P/Churyumov‐Gerasimenko, covering an energy range of a few eV/q to 40 keV/q. The low‐energy part of the data is, however, heavily distorted by the negatively charged spacecraft. In this study we use the Spacecraft Plasma Interaction Software to model the influence of the spacecraft potential on the ion trajectories and the corresponding distortion of the field of view (FOV) of the instrument. The results show that the measurements are not significantly distorted when the ion energy corresponds to at least twice the spacecraft potential. Below this energy the FOV is often heavily distorted, but the distortion differs between different viewing directions. Generally, ions entering the instrument close to the aperture plane are less affected than those entering with extreme elevation angles.

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  • 40.
    Bergman, Sofia
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics. Swedish Institute of Space Physics, Kiruna, Sweden.
    Stenberg Wieser, Gabriella
    Wieser, Martin
    Johansson, Fredrik Leffe
    Eriksson, Anders
    The Influence of Varying Spacecraft Potentials and Debye Lengths on In Situ Low-Energy Ion Measurements2020In: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 125, no 4, article id e2020JA027870Article in journal (Refereed)
    Abstract [en]

    Low‐energy ions are difficult to measure, mainly due to spacecraft charging. The ions areattracted to or repelled from the charged surface prior to detection, which changes both the energy andtravel direction of the ions. This results in distortions of the data, and the changed travel directions distort the effective field of view (FOV) of the instrument performing the measurements. The ion composition analyzer (RPC‐ICA) was measuring positive ions down to an energy of a few eV around comet67P/Churyumov‐Gerasimenko. Low‐energy ions play important parts in processes in the cometary environment, but the FOV of RPC‐ICA has been shown to get severely distorted at low ion energies. Several factors are believed to affect the distortion level. In this study we use the Spacecraft Plasma Interaction Software (SPIS) to investigate the influence of varying spacecraft potentials and Debye lengths on the FOV distortion of RPC‐ICA. We show that the distortion level is dependent on the Debye length of the surrounding plasma, but the sensitivity varies substantially between different viewing directions of the instrument. We also show that a small nonlinearity exists in the relation between FOV distortion, ion energy, and spacecraft potential, mainly caused by the photoemission and bulk flow of the cometary plasma.

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  • 41.
    Bergman, Sofia
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics. Swedish Institute of Space Physics, Kiruna, Sweden.
    Stenberg Wieser, Gabriella
    Swedish Institute of Space Physics, Kiruna, Sweden.
    Wieser, Martin
    Swedish Institute of Space Physics, Kiruna, Sweden.
    Nilsson, Hans
    Swedish Institute of Space Physics, Kiruna, Sweden.
    Vigren, Erik
    Swedish Institute of Space Physics, Uppsala, Sweden.
    Beth, Arnaud
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Masunaga, Kei
    Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency, Yoshinodai 3-1-1, Chuo-ku, Sagamihara, Kanagawa 252-5210, Japan.
    Eriksson, Anders
    Swedish Institute of Space Physics, Uppsala, Sweden.
    Flow directions of low-energy ions in and around the diamagnetic cavity of comet 67P2021In: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 507, no 4, p. 4900-4913Article in journal (Refereed)
    Abstract [en]

    The flow direction of low-energy ions around comet 67P/Churyumov–Gerasimenko has previously been difficult to constrain due to the influence of the spacecraft potential. The Ion Composition Analyzer of the Rosetta Plasma Consortium (RPC-ICA) on Rosetta measured the distribution function of positive ions with energies down to just a few eV/q throughout the escort phase ofthe mission. Unfortunately, the substantial negative spacecraft potential distorted the directional information of the low-energy data. In this work, we present the flow directions of low-energy ions around comet 67P, corrected for the spacecraft potential using Particle-In-Cell simulation results. We focus on the region in and around the diamagnetic cavity, where low-energy ions are especially important for the dynamics. We separate between slightly accelerated ‘burst’ features and a more constant ‘band’ of low-energy ions visible in the data. The ‘bursts’ are flowing radially outwards from the nucleus with an antisunward component while the ‘band’ is predominantly streaming back towards the comet. This provides evidence of counter-streaming ions, which has implications for the overall expansion velocity of the ions. The backstreaming ions are present also at times when the diamagnetic cavity was not detected, indicating that the process accelerating the ions back towards the comet is not connected to the cavity boundary.

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  • 42.
    Bergman, Sofia
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics. 1Swedish Institute of Space Physics, Kiruna, Sweden.
    Wieser, Gabriella Stenberg
    Wieser, Martin
    Johansson, Fredrik Leffe
    Vigren, Erik
    Nilsson, Hans
    Nemeth, Zoltan
    Eriksson, Anders
    Williamson, Hayley
    Ion bulk speeds and temperatures in the diamagnetic cavity of comet 67P from RPC-ICA measurements2021In: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 503, no 2, p. 2733-2745Article in journal (Refereed)
    Abstract [en]

    Comets are constantly interacting with the solar wind. When the comet activity is high enough, this leads to the creation of a magnetic field free region around the nucleus known as the diamagnetic cavity. It has been suggested that the ion-neutral drag force is balancing the magnetic pressure at the cavity boundary, but after the visit of Rosetta to comet 67P/Churyumov–Gerasimenko the coupling between ions and neutrals inside the cavity has been debated, at least for moderately active comets. In this study, we use data from the ion composition analyser to determine the bulk speeds and temperatures of the low-energy ions in the diamagnetic cavity of comet 67P. The low-energy ions are affected by the negative spacecraft potential, and we use the Spacecraft Plasma Interaction Software to model the resulting influence on the detected energy spectra. We find bulk speeds of 5–10 km s−1 with a most probable speed of 7 km s−1, significantly above the velocity of the neutral particles. This indicates that the collisional coupling between ions and neutrals is not strong enough to keep the ions at the same speed as the neutrals inside the cavity. The temperatures are in the range 0.7–1.6 eV, with a peak probability at 1.0 eV. We attribute the major part of the temperature to the fact that ions are born at different locations in the coma, and hence are accelerated over different distances before reaching the spacecraft.

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  • 43.
    Beth, Arnaud
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics. Department of Physics, Imperial College London, London, UK.
    Altwegg, K.
    Balsiger, H.
    Berthelier, J. -J.
    Combi, M. R.
    De Keyser, J.
    Fiethe, B.
    Fuselier, S. A.
    Galand, M.
    Gombosi, T. I.
    Rubin, M.
    Semon, T.
    ROSINA ion zoo at Comet 67P2020In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 642, article id A27Article in journal (Refereed)
    Abstract [en]

    Context: The Rosetta spacecraft escorted Comet 67P/Churyumov-Gerasimenko for 2 yr along its journey through the Solar System between 3.8 and 1.24 au. Thanks to the high resolution mass spectrometer on board Rosetta, the detailed ion composition within a coma has been accurately assessed in situ for the very first time.

    Aims: Previous cometary missions, such as Giotto, did not have the instrumental capabilities to identify the exact nature of the plasma in a coma because the mass resolution of the spectrometers onboard was too low to separate ion species with similar masses. In contrast, the Double Focusing Mass Spectrometer (DFMS), part of the Rosetta Orbiter Spectrometer for Ion and Neutral Analysis on board Rosetta (ROSINA), with its high mass resolution mode, outperformed all of them, revealing the diversity of cometary ions.

    Methods: We calibrated and analysed the set of spectra acquired by DFMS in ion mode from October 2014 to April 2016. In particular, we focused on the range from 13–39 u q−1. The high mass resolution of DFMS allows for accurate identifications of ions with quasi-similar masses, separating 13C+ from CH+, for instance.

    Results: We confirm the presence in situ of predicted cations at comets, such as CHm+ (m = 1−4), HnO+ (n = 1−3), O+, Na+, and several ionised and protonated molecules. Prior to Rosetta, only a fraction of them had been confirmed from Earth-based observations. In addition, we report for the first time the unambiguous presence of a molecular dication in the gas envelope of a Solar System body, namely CO2++.

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  • 44.
    Beth, Arnaud
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Gunell, Herbert
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Simon Wedlund, C.
    Goetz, C.
    Nilsson, H.
    Hamrin, Maria
    Umeå University, Faculty of Science and Technology, Department of Physics.
    First investigation of the diamagnetic cavity boundary layer with a 1D3V PIC simulation2022In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 667, article id A143Article in journal (Refereed)
    Abstract [en]

    Context: Amongst the different features and boundaries encountered around comets, one remains of particular interest to the plasma community: the diamagnetic cavity. Crossed for the first time at 1P/Halley during the Giotto flyby in 1986 and later met more than 700 times by the ESA Rosetta spacecraft around Comet 67P/Churyumov-Gerasimenko, this region, almost free of any magnetic field, surrounds nuclei of active comets. However, previous observations and modelling of this part of the coma have not yet provided a definitive answer as to the origin of such a cavity and on its border, the diamagnetic cavity boundary layer.

    Aims: We investigate which forces and equilibrium might be at play and balance the magnetic pressure at this boundary down to the spatial and temporal scales of the electrons in the 1D collisionless case. In addition, we scrutinise assumptions made in magneto-hydrodynamic and hybrid simulations of this environment and check for their validity.

    Methods: We simulated this region at the electron scale by means of 1D3V particle-in-cell simulations and SMILEI code.

    Results: Across this layer, depending on the magnetic field strength, the electric field is governed by different equilibria, with a thin double-layer forming ahead. In addition, we show that the electron distribution function departs from Maxwellian and/or gyrotropic distributions and that electrons do not behave adiabatically. We demonstrate the need to investigate this region at the electron scale in depth with fully kinetic simulations.

  • 45. Bingham, R
    et al.
    Shukla, Padma Kant
    Umeå University, Faculty of Science and Technology, Department of Physics. Institut für Theoretische Physik IV, Fakultät für Physik und Astronomie, Ruhr-Universität Bochum, D-44780 Bochum, Germany.
    Spicer, DS
    Coronal heating by dissipating current sheets2004In: Physica scripta. T, ISSN 0281-1847, Vol. T107, p. 247-249Article in journal (Refereed)
    Abstract [en]

    It is shown that the lower-hybrid turbulence produced by the lower-hybrid-drift wave instability at current sheets can heat electrons and ions in the solar corona. The waves heat the plasma particles by collisionless Landau damping. The waves resonate with electrons moving in the direction of the magnetic field, while they resonate with ions moving in the perpendicular direction.

  • 46. Björklund Svensson, Jonas
    et al.
    Guénot, Diego
    Ferri, Julien
    Ekerfelt, Henrik
    Gallardo González, Isabel
    Persson, Anders
    Svendsen, Kristoffer
    Veisz, Laszlo
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Lundh, Olle
    Low-divergence femtosecond X-ray pulses from a passive plasma lens2021In: Nature Physics, ISSN 1745-2473, E-ISSN 1745-2481, Vol. 17, no 5, p. 639-645Article in journal (Refereed)
    Abstract [en]

    Electron and X-ray beams originating from compact laser-wakefield accelerators have very small source sizes that are typically on the micrometre scale. Therefore, the beam divergences are relatively high, which makes it difficult to preserve their high quality during transport to applications. To improve on this, tremendous efforts have been invested in controlling the divergence of the electron beams, but no mechanism for generating collimated X-ray beams has yet been demonstrated experimentally. Here we propose and realize a scheme where electron bunches undergoing focusing in a dense, passive plasma lens can emit X-ray pulses with divergences approaching the incoherent limit. Compared with conventional betatron emission, the divergence of this so-called plasma lens radiation is reduced by more than an order of magnitude in solid angle, while maintaining a similar number of emitted photons per electron. This X-ray source offers the possibility of producing brilliant and collimated few-femtosecond X-ray pulses for ultra-fast science, in particular for studies based on X-ray diffraction and absorption spectroscopy.Main

  • 47.
    Brinkfeldt, Klas
    Umeå University, Faculty of Science and Technology, Space Science.
    Instrumentation for energetic Neutral atom measurements at Mars, Venus and The Earth2005Doctoral thesis, monograph (Other academic)
    Abstract [en]

    This thesis deals with the development and calibrations of sensors to measure energetic neutral atoms (ENAs) at Mars, Venus, and the Earth. ENAs are formed in charge exchange processes between energetic, singly--charged ions and a cold neutral gas. Since ENAs can travel in long straight trajectories, unaffected by electric or magnetic fields, they can be used to remotely image plasma interactions with neutral atmospheres. ENA instrument techniques have matured over the last decade and ENA images of the Earth's ring current for example, have successfully been analyzed to extract ion distributions and characterize plasma flows and currents in the inner magnetosphere.

    Three different ENA sensors have been developed to image ENAs at Mars, Venus, and the Earth. Two of them, the nearly identical Neutral Particle imagers (NPIs) are on-board the Mars Express and Venus Express spacecraft as a part of the Analyzer of Space Plasmas and Energetic Atoms (ASPERA-3 and 4) instruments. The third is the Neutral Atom Detector Unit, NUADU, aboard the TC-2 spacecraft of the Double Star mission. The NPI design is based on a surface reflection technique to measure low energy (~0.3-60 keV) ENAs, while the NUADU instrument is based on a simple design with large geometrical factor and solid state detectors to measure high energy ENAs (~20-300 keV).

    The calibration approach of both NPI sensors were to define the detailed response, including properties such as the angular response function and efficiency of one reference sensor direction then find the relative response of the other sensor directions. Because of the simple geometry of the NUADU instrument, the calibration strategy involved simulations to find the cutoff energy, geometrical factor and angular response. The NUADU sensor head was then calibrated to find the response to particles of different mass and energy. The NPI sensor for the Mars Express mission revealed a so-called priority effect in the sensor that lowers the angular resolution at high detector bias. During the calibration of the Venus Express NPI sensor tests were made which showed that the priority effect is a result of low amplitude (noise) pulses generated in the detector system. The conclusion is that the effect is caused by capacitive couplings between different anode sectors of the sensor. The thresholds on the preamplifiers were set higher on the Venus Express NPI, which removed the priority effect.

    Two of the three ENA experiments, the Double Star NUADU instrument and the Mars Express NPI sensor, have successfully measured ENAs that are briefly described in the thesis. The first ENA measurements at Mars were performed with Mars Express. Initial results from the NPI include measurements of ENAs formed in the Martian magnetosheath and solar wind ENAs penetrating to the nightside of Mars. The first results from NUADU in Earth orbit show the expected ENA emissions from a storm time ring current. Also, together with the HENA instrument on the IMAGE spacecraft, NUADU have produced the first multi-point ENA image of the ring current.

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  • 48.
    Brodin, Gert
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Al-Naseri, Haidar
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Zamanian, Jens
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Torgrimsson, Greger
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Eliasson, Bengt
    SUPA, Department of Physics, University of Strathclyde, Glasgow, United Kingdom.
    Plasma dynamics at the Schwinger limit and beyond2023In: Physical review. E, ISSN 2470-0045, E-ISSN 2470-0053, Vol. 107, no 3, article id 035204Article in journal (Refereed)
    Abstract [en]

    Strong field physics close to or above the Schwinger limit are typically studied with vacuum as initial condition or by considering test particle dynamics. However, with a plasma present initially, quantum relativistic mechanisms such as Schwinger pair creation are complemented by classical plasma nonlinearities. In this work we use the Dirac-Heisenberg-Wigner formalism to study the interplay between classical and quantum mechanical mechanisms in the regime of ultrastrong electric fields. In particular, the effects of initial density and temperature on the plasma oscillation dynamics are determined. Finally, comparisons with competing mechanisms such as radiation reaction and Breit-Wheeler pair production are made.

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  • 49.
    Brodin, Gert
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Ekman, Robin
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Zamanian, Jens
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Do hydrodynamic models based on time-independent density functional theory misestimate exchange effects?: Comparison with kinetic theory for electrostatic waves2019In: Physics of Plasmas, ISSN 1070-664X, E-ISSN 1089-7674, Vol. 26, no 9, article id 092113Article in journal (Refereed)
    Abstract [en]

    We have extended previous quantum kinetic results to compute the exchange correction to the electrostatic electron susceptibility for arbitrary frequencies and wavenumbers in the low temperature limit. This has allowed us to make a general comparison with a much used hydrodynamic expression, based on density functional theory, for exchange effects. For low phase velocities, as for ion-acoustic waves, wave-particle interaction leads to a strong enhancement of the exchange correction and the hydrodynamic result is smaller by an order of magnitude. The hydrodynamic expression gives a useful approximation when the phase velocity is 2.5 times the Fermi velocity. If this condition is not fulfilled, the hydrodynamical theory gives misleading results. We discuss the implications of our results for the model choice for quantum plasmas, especially regarding particle dispersive effects.

  • 50.
    Brodin, Gert
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Ekman, Robin
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Zamanian, Jens
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Nonlinear wave damping due to multi-plasmon resonances2018In: Plasma Physics and Controlled Fusion, ISSN 0741-3335, E-ISSN 1361-6587, Vol. 60, no 2, article id 025009Article in journal (Refereed)
    Abstract [en]

    For short wavelengths, it is well known that the linearized Wigner-Moyal equation predicts wave damping due to wave-particle interaction, where the resonant velocity shifted from the phase velocity by a velocity v(q) = hk/2m. Here h is the reduced Planck constant, k is the wavenumber and m is the electron mass. Going beyond linear theory, we find additional resonances with velocity shifts nv(q), n= 2,3, ..., giving rise to a new wave-damping mechanism that we term multi-plasmon damping, as it can be seen as the simultaneous absorption (or emission) of multiple plasmon quanta. Naturally this wave damping is not present in classical plasmas. For a temperature well below the Fermi temperature, if the linear (n = 1) resonant velocity is outside the Fermi sphere, the number of linearly resonant particles is exponentially small, while the multi-plasmon resonances can be located in the bulk of the distribution. We derive sets of evolution equations for the case of two-plasmon and three-plasmon resonances for Langmuir waves in the simplest case of a fully degenerate plasma. By solving these equations numerically for a range of wave-numbers we find the corresponding damping rates, and we compare them to results from linear theory to estimate the applicability. Finally, we discuss the effects due to a finite temperature.

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