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  • 1
    Digitale Medien
    Digitale Medien
    Quasi-thermal fluctuations in a beam-plasma system (1996)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 3 (1996), S. 1234-1240 
    Details
    ISSN: 1089-7674
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: The quasi-thermal electrostatic field fluctuations of a stable unmagnetized electron beam-plasma system is considered. Both the beam and the background plasma are modeled as isotropic Maxwellians. Both the normal modes of the plasma and the contributions from other modes are considered. The dependence of these fluctuations on beam velocity, density, and temperature are examined. The implications of these waves for real beam-plasma systems are also discussed. © 1996 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.871747
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  • 2
    Digitale Medien
    Digitale Medien
    The propagation of a dense quasi-neutral ion beam across a magnetized plasma (1985)
    Springer
    Astrophysics and space science 110 (1985), S. 371-378 
    Details
    ISSN: 1572-946X
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Physik
    Notizen: Abstract Propagation of a quasi-neutral narrow ion beam across a magnetised cold plasma is investigated in slab geometry. This problem is of interest in connection with artificial beam injection experiments and with naturally appearing plasma injections into magnetic fields as astrophysical jets. Several different cases are discussed briefly where the beam is assumed either slow or fast. For fast beams it is shown that they propagate due to generation of a polarisation electric field even in the case of presence of a background plasma. Slow beams can depolarise by currents flowing into the beam along the field lines and providing the required electrons for charge neutralisation. Some implications of the model are discussed in the context of recent active beam injection experiments into space plasma.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00653683
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  • 3
    Digitale Medien
    Digitale Medien
    Adiabatic-drift-loss modification of the electromagnetic loss-cone instability for anisotropic plasma (1980)
    Springer
    Astrophysics and space science 72 (1980), S. 97-110 
    Details
    ISSN: 1572-946X
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Physik
    Notizen: Abstract Observation of the adiabatic behaviour of energetic particle pitch-angle distributions in the magnetosphere (Lyons, 1977, and others) in the past indicated the development of pronounced minima or drift-loss cones on the pitch-angle distributions centred at α≃90° in connection with storm-time changes in magnetospheric convection and magnetic field. Using a model of a drift-modified loss-cone distribution (MLCD) of the butterfly type, the linear stability of electromagnetic whistler or ion-cyclotron waves propagating parallel to the magnetic field has been investigated. The instability is shown to be quenched at high frequencies ω〈ω m =A/(A+1), whereA is the thermal anisotropy. This quenching becomes stronger the higher are the respective parallel hot particle thermal velocityA h″ and cold plasma densityn c . Particles around pitch-angles α≃90° are identified as generating electromagnetic cyclotron waves near the marginally stable frequency ω m . It is concluded that the absence of electromagnetic VLF and ELF noise during times when MLCD develops is the result of the shift of the unstable spectrum to low frequencies.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00642168
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  • 4
    Digitale Medien
    Digitale Medien
    Waveform and packet structure of lion roars (1999)
    Springer
    Annales geophysicae 17 (1999), S. 1528-1534 
    Details
    ISSN: 0992-7689
    Schlagwort(e): Interplanetary physics (MHD waves and turbulence ; plasma waves and turbulence)
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Geologie und Paläontologie , Physik
    Notizen: Abstract The Equator-S magnetometer is very sensitive and has a sampling rate of normally 128 Hz. The high sampling rate allows for the first time fluxgate magnetometer measurements of ELF waves between the ion cyclotron and the lower hybrid frequencies in the equatorial dayside magnetosheath. The so-called lion roars, typically seen by the Equator-S magnetometer at the bottom of the magnetic troughs of magnetosheath mirror waves, are near-monochromatic packets of electron whistler waves lasting for a few wave cycles only, typically 0.25 s. They are right-hand circularly polarized waves with typical amplitudes of 0.5–1 nT at around one tenth of the electron gyrofrequency. The cone angle between wave vector and ambient field is usually smaller than 1.5°.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/s00585-999-1528-9
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  • 5
    Digitale Medien
    Digitale Medien
    Magnetospheric lion roars (2000)
    Springer
    Annales geophysicae 18 (2000), S. 406-410 
    Details
    ISSN: 0992-7689
    Schlagwort(e): Magnetospheric physics (magnetospheric configuration and dynamics MHD waves and instabilities plasma waves and instabilities)
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Geologie und Paläontologie , Physik
    Notizen: Abstract The Equator-S magnetometer is very sensitive and has a sampling rate normally of 128 Hz. The high sampling rate for the first time allows detection of ELF waves between the ion cyclotron and the lower hybrid frequencies in the equatorial dawnside magnetosphere. The characteristics of these waves are virtually identical to the lion roars typically seen at the bottom of the magnetic troughs of magnetosheath mirror waves. The magnetospheric lion roars are near-monochromatic packets of electron whistler waves lasting for a few wave cycles only, typically 0.2 s. They are right-hand circularly polarized waves with typical amplitudes of 0.5 nT at around one tenth of the electron gyrofrequency. The cone angle between wave vector and ambient field is nearly always smaller than 1°.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/s00585-000-0406-2
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  • 6
    Digitale Medien
    Digitale Medien
    Third plasma harmonic radiation in type II bursts (1992)
    Springer
    Solar physics 140 (1992), S. 149-160 
    Details
    ISSN: 1573-093X
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Physik
    Notizen: Abstract We present observational evidence for simultaneous fundamental, second and third harmonic radio emission during an excessively strong type II burst on February 16, 1984. This burst was emitted from an active region behind the limb allowing for fair resolution of the wave bands. If interpreted as a triple harmonic system, three different, nearly equally probable mechanisms for higher harmonic emission are qualitatively discussed. These are a four-wave process which involves very strong Langmuir waves, a decay process first proposed by Cairns (1987) for higher harmonic emission near the Earth's bow shock, and time evolution of the emitted frequency during Langmuir wave collapse. In sufficiently strong coronal shock waves, both of the former mechanisms may be more efficient than under solar wind conditions. In the third mechanism, Langmuir wave collapse may be driven by strong electron beams as are expected to exist in quasiparallel shocks where electron reflection may be strongest. We discuss the differences between the signatures of these mechanisms.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00148435
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  • 7
    Digitale Medien
    Digitale Medien
    The Low-Latitude Boundary Layer at the Flanks of the Magnetopause (1997)
    Springer
    Space science reviews 80 (1997), S. 341-367 
    Details
    ISSN: 1572-9672
    Schlagwort(e): Magnetopause ; Boundary Layer ; Reconnection ; Kelvin-Helmholtz-Instability ; Diffusion
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Physik
    Notizen: Abstract This is a brief overview on what we know and do not know about the low-latitude boundary layer (LLBL) at the flanks of the magnetotail. On the basis of recent observations, simulations and theories we conclude that reconnection is the dominant process in generating the LLBL and its structure probably even under northward IMF conditions. Part of the LLBL always seems to be on open field lines. Possibly the LLBL possesses a double structure with its outer part open and inner part closed. Anomalous diffusive processes cannot sustain the LLBL but provide sufficient diffusivity for reconnection. Strong diffusion is only expected in narrow localized regions and can make the transition to superdiffusion. Kelvin-Helmholtz instability (KHI) is favoured for northward IMF, producing vortices at the tail flanks. Its contribution to efficient mass transport still remains questionable. Coupling of the LLBL to the ionosphere can strongly affect the internal structure of the LLBL, causing turbulent eddies and detachments of plasma blobs as also field-aligned currents and electron heating. The structure and dynamics of the LLBL are affected by field-aligned electric potentials that decouple the LLBL from the ionosphere. Non-ideal coupling simulations suggest that the dusk flank is decoupled, favouring KHI, while the dawn flank is dominated by currents and turbulence.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1004986323461
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  • 8
    Digitale Medien
    Digitale Medien
    Plasma waves at the dayside magnetopause (1988)
    Springer
    Space science reviews 47 (1988), S. 175-202 
    Details
    ISSN: 1572-9672
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Physik
    Notizen: Abstract Experimental investigations of plasma waves at the magnetopause, including recent results from the AMPTE/IRM satellite, show that both δE and δB fluctuations typically have a featureless spectrum which monotonically decreases with frequency; integrated rms amplitudes are typically a few mV m-1 for δE and 10 nT for δB, though in particular δE can be as much as an order of magnitude larger in exceptional cases. Surveys show a lack of correlation between wave parameters and the magnetopause parameters. Under the assumption that crossing the diffusion region would give a pronounced signature in the waves, the survey data allow an upper limit to be placed on the latitudinal extent of the diffusion region, which is about 1000 km — implying that it is not surprising that the wave data surveys have so far failed to detect it. The observed wave turbulence levels have been used to estimate diffusion coefficients under different assumptions for the wave mode, but the resulting diffusion coefficient is always too small to explain either reconnection or boundary layer formation. Recent work of Galeev et al. (1986) indicates that the dominant diffusion process may be ‘magnetic field migration’, which is a macroscopic process involving the interaction of tearing mode islands. Assuming this mode to be present at the observed level of δB, a particle diffusion coefficient of nearly 109 m2 s-1 is obtained. Another macroscopic diffusive process which could occur at the magnetopause is stochastic E × B scattering, which also implies a diffusion coefficient the order of 109 m2 s-1 if the observed δE spectrum is assumed to be a turbulent cascade consisting of convective cells.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00223240
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