| 1. |
- Blomberg, Lars G., et al.
(författare)
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The martian plasma environment : Electric field and Langmuir probe diagnostics
- 2003
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Ingår i: IEEE Transactions on Plasma Science. - : Institute of Electrical and Electronics Engineers (IEEE). - 0093-3813 .- 1939-9375. ; 31:6, s. 1232-1236
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Tidskriftsartikel (refereegranskat)abstract
- The plasma environment of Mars has been studied by a small handful of spacecraft. From the sparse observations that exist, one may conclude that the solar wind-Martian magnetosphere interaction is different in significant ways from the solar wind's interaction with Earth's magnetosphere. Mars offers an opportunity to make significant advances in our understanding of the fundamentals of the solar wind's interaction with cold celestial bodies, with suitable plasma instrumentation orbiting the planet. We briefly review what is known about Mars' plasma environment and address some scientific topics that can be studied by proper plasma instrumentation in Mars' vicinity, in particular the scientific potential of Langmuir probe measurements. Finally, we exemplify how the studies may contribute to an enhanced understanding not only of the plasma surrounding Mars, but also of the planet itself and its neutral atmosphere.
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| 2. |
- Brenning, Nils
(författare)
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Interaction between a dust cloud and a magnetized plasma in relative motion
- 2001
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Ingår i: IEEE Transactions on Plasma Science. - : Institute of Electrical and Electronics Engineers (IEEE). - 0093-3813 .- 1939-9375. ; 29:2, s. 302-306
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Tidskriftsartikel (refereegranskat)abstract
- The interaction between a dust cloud and a magnetized plasma is investigated by use of an idealized model where the dust particles have uniform size, a uniform density within the dust cloud, and start with the same velocity across the magnetic field in the plasma's rest frame. The interaction is found to be governed by a dimensionless parameter K which is a function of dust cloud, and ambient plasma, parameters. For K much smaller than unity, the interaction goes on for typically 1/(2 piK) gyro times, with the particles in the dust cloud performing gyro motions with decreasing radius, For K close to unity, the dust motion is stopped on the order of a dust particle gyro time, For the case K much greater than 1, the plasma in the flux tube through the dust cloud is dragged across the magnetic field over a distance of the order of Kr-d, where r(d) is the dust gyro radius, before the motion is stopped. Some expected effects for a more realistic dust cloud with density gradients, and containing dust with a spread in size, are discussed. The results have bearing on dusty plasma in space, e.g., models of the formation of spokes in Saturn's ring system.
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| 3. |
- Dieckmann, Mark E, 1969-, et al.
(författare)
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Three-dimensional visualization of electron acceleration in a magnetized plasma
- 2002
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Ingår i: IEEE Transactions on Plasma Science. - 0093-3813 .- 1939-9375. ; 30:1 I, s. 20-21
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Tidskriftsartikel (refereegranskat)abstract
- We examine wave-particle interactions in a magnetized plasma. We present snapshots of an animation of the three-dimensional electron phase space distribution produced by an electrostatic wave propagating across a magnetic field. The distribution function has been evolved by a particle in cell simulation. The electron phase space has been visualized by distributing the simulation electrons over an array representing phase space density and by volume rendering this array. The results are, due to the choice of initial plasma and wave parameters, of relevance for electron acceleration at astrophysical shocks.
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| 4. |
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| 5. |
- Raadu, Michael A.
(författare)
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Effective distribution functions for electrostatic waves in dusty plasmas with a dust-size distribution
- 2001
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Ingår i: IEEE Transactions on Plasma Science. - : Institute of Electrical and Electronics Engineers (IEEE). - 0093-3813 .- 1939-9375. ; 29:2, s. 182-185
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Tidskriftsartikel (refereegranskat)abstract
- The kinetic theory for the electrostatic modes of dusty plasmas with a distribution of grain sizes is examined. It is assumed that the size distribution predominantly decreases exponentially with the mass for large sizes, and that a power law prevails for small sizes. Thermodynamic equilibrium leads to Maxwellian distributions over velocity with a fixed temperature and continuously varying mass. Smaller particles have higher thermal velocity and dominate the tail of the velocity distribution. The contribution of the dust component to the dispersion function is found to be non-Maxwellian and is equivalent to that for a kappa (generalized Lorentzian) distribution of monosized particles, Known results for kappa distributions may be exploited, However, the nonlinear response of the charge density of the dust to an electrostatic potential is quite different to that of a monosized kappa distribution. In general, the definition of an effective dust distribution function for linearized electrostatic modes leads to a useful straightforward procedure to find the dispersion function. It is important to realize that the combined effects of velocity and size distribution can, in general, strongly modify the kinetic behavior of the plasma dust component.
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| 6. |
- Ratynskaia, Svetlana V., et al.
(författare)
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Dust mode in collisionally dominated complex plasmas with particle drift
- 2004
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Ingår i: IEEE Transactions on Plasma Science. - : Institute of Electrical and Electronics Engineers (IEEE). - 0093-3813 .- 1939-9375. ; 32:2, s. 613-616
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Tidskriftsartikel (refereegranskat)abstract
- Experiments with flow of microparticles were conducted in a de discharge. A sharp threshold in the neutral gas pressure for the onset of an unstable low-frequency dust wave mode was observed. Highly space- and time-resolved measurements of the microparticle flow combined with probe measurements of the plasma parameters have allowed detailed comparison with a theoretical model. The model demonstrates good qualitative and quantitative agreement with the experimental results providing accurate estimates of the particle charge.
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| 7. |
- Rothwell, P L, et al.
(författare)
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The role of O+ ions in channeling solar wind energy to the ionosphere
- 2000
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Ingår i: IEEE Transactions on Plasma Science. - : Institute of Electrical and Electronics Engineers (IEEE). - 0093-3813 .- 1939-9375. ; 28, s. 1912-1919
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Tidskriftsartikel (refereegranskat)abstract
- In space weather prediction, the transport of solar wind energy through the magnetosphere is a major aspect. For the transport of energy from the magnetosphere to the ionosphere, magnetic field-aligned (Birkeland) currents are a very important agent. In the present paper, we discuss the role of O+ ions for driving field-aligned currents of spatially alternating polarity that may explain multiple auroral arcs, It is known from earlier work that nonadiabatic motion of O+ ions in the magnetotail plasma can lead to the formation of density striations that are stationary in the GSM frame, As the magnetospheric plasma drifts through these density striations, magnetic field-aligned currents of alternating signs are forced to flow in and out of the oxygen-rich region to maintain quasineutrality. This generates Alfven waves that propagate in the drifting plasma but can form stationary structures in the GSM frame. As the currents close in the ionosphere, the equatorial plasma constitutes a generator from which spatially alternating magnetic field-aligned currents carry energy to the ionospheric load, The wavelength of the density striations, mapped to the ionosphere, is compatible with the spacing of stable auroral arcs, and the power supplied by the equatorial generator region is estimated to be compatible with what is needed to drive auroral arcs, Thus, the consequences of nonadiabatic motion of O+ ions may explain how part of the energy extracted from the solar wind is channeled into multiple auroral arcs.
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| 8. |
- Shafiq, Mohammad, et al.
(författare)
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Delayed shielding of a test charge due to dynamical grain charging in a dusty plasma
- 2004
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Ingår i: IEEE Transactions on Plasma Science. - 0093-3813 .- 1939-9375. ; 32, s. 627-631
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Tidskriftsartikel (refereegranskat)abstract
- The dynamical charging of grains in a dusty plasma modifies the plasma dielectric response function and the nature of the electrostatic wave modes. The grain charging leads to an additional shielding effect that acts in the same way as Debye shielding. Both the additional shielding and the charging rate are important in determining the response of a dusty plasma to a moving test charge. The dynamics of the charging can be approximated by using a time delay. An alternative analysis of the potential of a slowly moving test charge is performed introducing a delay operator for the grain charge response. The terms in the potential that depend on the charging dynamics involve a spatial shift given by the test charge velocity and the charging time. This gives a physical interpretation of earlier results which are identical to first order in the test charge velocity.
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| 9. |
- Ynnerman, Anders, et al.
(författare)
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Bifurcation to chaos in charged particle orbits in a magnetic reversal with shear field
- 2002
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Ingår i: IEEE Transactions on Plasma Science. - : Institute of Electrical and Electronics Engineers (IEEE). - 0093-3813 .- 1939-9375. ; 30:1 I, s. 18-19
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Tidskriftsartikel (refereegranskat)abstract
- Regular and stochastic behavior in single particle orbits in static magnetic reversals have wide application in laboratory and physical plasmas. In a simple magnetic reversal, the system has three degrees of freedom but only two global (exact) constants of the motion, the system is nonintegrable and the particle motion can, under certain conditions, exhibit chaotic behavior. Here, we consider the dynamics when a constant shear field is added. In this case, the form of the potential changes from quadratic to velocity dependent. We use numerically integrated trajectories to show that the effect of the shear field is to break the symmetry of the system so that the topology of the invariant tori of regular orbits is changed. In this case, invariant tori take the form of nested Moebius strips in the presence of the shear field. The route to chaos is via bifurcation (period doubling) of the Moebius strip tori.
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| 10. |
- Sarimov, R, et al.
(författare)
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Nonthermal GSM microwaves affect chromatin conformation in human lymphocytes similar to heat shock
- 2004
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Ingår i: IEEE Transactions on Plasma Science. - 0093-3813. ; 32:4, s. 1600-1608
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Tidskriftsartikel (refereegranskat)abstract
- Here we investigated whether microwaves (MWs) of Global System for Mobile Communication (GSM) induce changes in chromatin conformation in human lymphocytes. Effects of MWs were studied at different frequencies in the range of 895-915 MHz in experiments with lymphocytes from seven healthy persons. Exposure was performed in transverse electromagnetic transmission line cell (TEM-cell) using a GSM test-mobile phone. All standard modulations included 2 W output power in the pulses, specific absorbed rate (SAR) being 5.4 mW/kg. Changes in chromatin conformation, which are indicative of stress response and genotoxic effects, were measured by the method of anomalous viscosity time dependencies (AVTD). Heat shock and treatment with the genotoxic agent camptothecin, were used as positive controls. 30-min exposure to MWs at 900 and 905 MHz resulted in statistically significant condensation of chromatin in lymphocytes from 1 of 3 tested donors. This condensation was similar to effects. of heat shock within the temperature window of 40degreesC-44degreesC. Analysis of pooled data from all donors showed statistically significant effect of 30-min exposure to MWs. Stronger effects of MWs was found following I-h exposure. In replicated experiments, cells from four out of five donors responded to 905 MHz. Responses to 915 MHz were observed in cells from I out of 5 donors, p < 0.002. Dependent on donor, condensation, 3 donors, or decondensation, 1 donor, of chromatin was found in response to I-h exposure. Analysis of pooled data from all donors showed statistically significant effect of 1-h exposure to MWs. In cells from one donor, this effect was frequency-dependent (p < 0.01). Effects of MWs correlated statistically significantly with effects of heat shock and initial state of chromatin before exposure. MWs at 895 and 915 MHz affected chromatin conformation in transformed lymphocytes. The conclusion-GSM microwaves under specific conditions of exposure affected human lymphocytes similar to stress response. The data suggested that the MW effects differ at various GSM frequencies and vary between donors.
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