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S. Mazevet M. Challacombe P. M. Kowalski D. Saumon 《Astrophysics and Space Science》2007,307(1-3):273-277
We investigate the conductivity of warm dense helium under conditions found in the atmospheres of cool white dwarfs using
ab initio simulations. The calculations performed consist of quantum molecular dynamics simulations where the electronic wavefunction
at each time step is obtained using density functional theory, while the ion trajectories are calculated using the resulting
quantum mechanical forces. We use both conventional DFT (PW91) and hybrid (PBE0) functionals to calculate the conductivities
that provide an estimate of the ionization fraction. While the calculations are in good agreement with the measurements for
the equation of state, a significant discrepancy exists with the recently measured conductivity. 相似文献
3.
Characteristics of the astrophysical important Stark broadened 388.86 nm, 471.32 nm and 501.56 nm He I spectral line profiles have been measured at electron densities between 4.4·1022 and 8.2·1022 m−3 and electron temperatures between 18,000 and 33,000 K in plasmas created in five various discharge conditions using a linear, low-pressure, pulsed arc as an optically thin and reproductive plasma source operated in a helium–nitrogen–oxygen gas mixture. On the basis of the observed asymmetry of the line profiles, we have obtained their ion broadening parameters (A) caused by influence of the ion microfield and also the influence of the ion dynamic effect (D) to the line shape. Our A and D parameters represent the first data obtained experimentally by the use of the line profile deconvolution procedure. We have found stronger influence of the ion contribution to these He I line profiles than the semiclassical theoretical approximation provides. This can be important for some astrophysical plasma modelling or for diagnostics. 相似文献
4.
In this article, an asymmetric counterstreaming distribution function is investigated on the basis of three-dimensional relativistic
particle-in-cell simulations for wave propagation at an oblique angle with respect to the axis of the counterstream. For such
asymmetric distribution functions, any linear Weibel modes must be isolated and therefore restricted to discrete wavenumber
values. Using analytical linear Vlasov theory, this result has recently been proven generally, and has been illustrated by
the example of an electron beam counterstreaming with a positron beam. By the means of self-consistent particle-in-cell simulations,
in this paper a realistic distribution function is investigated that consists of neutral asymmetric Maxwellian counterstreams.
For this scenario, the existence of isolated modes can be confirmed, especially when compared to the case of symmetric counterstreams.
相似文献
5.
Dieter Biskamp 《Astrophysics and Space Science》1996,242(1-2):165-207
A review of the present status of the theory of magnetic reconnection is given. In strongly collisional plasmas reconnection proceeds via resistive current sheets, i.e. quasi-stationary macroscopic Sweet-Parker sheets at intermediate values of the magnetic Reynolds numberR
m
, or mirco-current sheets in MHD turbulence, which develops at highR
m
. In hot, dilute plasmas the reconnection dynamics is dominated by nondissipative effects, mainly the Hall term and electron inertia. Reconnection rates are found to depend only on the ion mass, being independent of the electron inertia and the residual dissipation coefficients. Small-scale whistler turbulence is readily excited giving rise to an anomalous electron viscosity. Hence reconnection may be much more rapid than predicted by conventional resistive theory. 相似文献
6.
Csar A. Mendoza-Briceo Miguel H. Ibez Valery M. Nakariakov 《Dynamics of Atmospheres and Oceans》2001,34(2-4)
The weakly nonlinear evolution of quasi-isentropic magnetoacoustic waves in the solar atmosphere is analyzed. The plasma is assumed to be initially homogeneous, in thermal equilibrium and with a straight and homogeneous magnetic field frozen in. Additionally, the plasma is assumed to be cooled by the standard cooling function in the range of 104 K<T<107 K and heated by a mechanism which is proportional to the density and temperature. The range of temperature where the plasma is isentropically unstable, the e-folding time for thermal instability and the corresponding time and length-scale for wave breaking are found. 相似文献
7.
Colliding Blast Waves Driven by the Interaction of a Short-Pulse Laser with a Gas of Atomic Clusters
Roland A. Smith James Lazarus Matthias Hohenberger Alastair S. Moore Joseph S. Robinson Edward T. Gumbrell Mike Dunne 《Astrophysics and Space Science》2007,307(1-3):131-137
Collisions between shocks are commonly found in many astrophysical objects, however robust numerical models or laboratory
analogues of these complex systems remain challenging to implement. We report on the development of scaled laboratory experiments
which employ new techniques for launching and diagnosing colliding shocks and high Mach number blast waves, scalable to a
limited subset of astrophysically-relevant regimes. Use of an extended medium of atomic clusters enables efficient (>80%)
coupling of 700 fs, 1 J, 1054 nm laser pulses to a “cluster” gas with an average density of ≈1019 particles cm−3, producing an initial energy density >105 J cm−3, equivalent to ≈5×109 J/g. Multiple laser foci are used to tailor the spatial profile of energy deposition, or to launch pairs of counter-propagating
cylindrical shocks which then collide. By probing the collision interferometrically at multiple view angles in 5^ increments and applying an inverse Radon transform to the resulting phase projections we have been able to tomographicall
reconstruct the full three-dimensional, time-framed electron density profile of the system. 相似文献
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We investigate the effect of the plume/interplume lane (PIPL) structure of the solar polar coronal hole (PCH) on the propagation characteristics of ion-cyclotron waves (ICW). The gradients of physical parameters determined by SOHO and TRACE satellites both parallel and perpendicular to the magnetic field are considered with the aim of determining how the efficiency of the ICR process varies along the PIPL structure of PCH. We construct a model based on the kinetic theory by using quasi-linear approximation. We solve the Vlasov equation for O VI ions and obtain the dispersion relation of ICW. The resonance process in the interplume lanes is much more effective than in the plumes, agreeing with the observations which show the source of fast solar wind is interplume lanes. The solution of the Vlasov equation in PIPL structure of PCH, the physical parameters of which display gradients along and perpendicular direction to the external magnetic field, is thus obtained in a more general form than the previous investigations. 相似文献
10.
The transformation of upper-hybrid, lower-hybrid, and magnetosonic waves on a heavy charged particle lying at the plane boundary of a magnetoactive plasma is considered. The angular distribution of the radiation resulting from wave transformation is investigated. The transformation of a low-frequency magnetosonic wave is suggested as a possible mechanism for pulsar radio emission. 相似文献