Sheath-limited unipolar induction in the solar wind

The collection of charged particles by electrodes in plasmas is controlled by the currentvoltage characteristics of the plasma sheath which forms at the electrode surface. This principle is applied to the steady-state electromagnetic interaction of the solar wind with moon-like bodies, or ‘solid-body’ interactions. In some cases the unipolar dynamo response of an electrically conducting body in the solar wind motional electric field can be controlled by sheath effects. This occurs for highly conducting bodies when the body radiusR is less than a critical valueR _c , with the result that no induced bow shock wave can form. For the Moon and MercuryR/R _c ?1, so that sheath effects do not limit their unipolar responses. The asteroids are found to be either too cold or too small to maintain steady-state induced magnetospheres. The Martian satellites, the irregular Jovian satellites, and the outer satellites of Saturn also haveR/R _c ?1. No bow shock waves should be generated by these bodies, unless they are highly magnetized or have large magnetic permeabilities. Unipolar induction heating of meteorite parent bodies in a primordial enhanced solar wind should not be inhibited by sheath effects, providedR?50 m.     

Erroneous evaluation of electron and ion temperatures from a contaminated retarding potential trap

Contaminated electrode effects of a retarding potential trap on the temperature measurement are investigated in laboratory plasma. It is shown that poorly conductive layers on the electrode surface modify the v-i curves. This contamination effect of RPT electrode can be overcome either by increasing the sweep-rate of the grid potential or by the use of a large effective sheath resistance.     

A numerical study of local stellar motions

The orbits of over 10000 stars are integrated in a steady-state model of the Galaxy for a time 6.0×10⁸ yr. Initially, the stars are placed randomly inside spheres of 500 pc and 50 pc radius and are given random velocities, such that the sample has a Maxwellian or a spheroidal velocity distribution. The spheres are placed at the Sun's distance from the galactic centre (10 kpc) and are given a circular velocity of 250 km s^?1. The mean velocities and dispersions of stars within 1 kpc of an ‘observer’ moving at the circular velocity are calculated as functions of time. The quantities show a strong time-dependence with oscillations of period 10⁸ yr. The oscillations are independent of the mass model and occur also in an inverse square force field. A vertex deviation of the velocity ellipsoid, an asymmetric drift and aK-effect occur as natural consequences of the oscillations. Attempts to apply the Oort method for density determinations in the galactic plane are also influenced by the oscillations. Spiral density waves appear to have a small effect on the motions of the test stars.     

The effects of the polytropic coefficient on plasma sheath in two cases isothermal and adiabatic ion thermal flow

Recently it has been shown that for finite and small values of the electron Debye length, the ion polytropic coefficient is approached to some constant value in the plasma sheath region by decreasing the plasma density. In this paper, using a plasma multi fluid model, the effect of ion polytropic coefficient γ _i on the plasma sheath structure have been examined. The numerical calculations of the basic equation of the model show that the polytropic coefficient strongly affects on the plasma sheath characteristics. The results show that by transition from an isothermal flow (γ _i =1) to an adiabatic flow (γ _i =3), the net current to the wall and the electric potential distribution increase and the sheath width decreases in a thermal plasma sheath.     

Electric charge of grains and interstellar radioactivity

We investigate the electric potential of high speed interstellar grains trapping radioactive nuclei which are suggested to exist in interstellar medium by the study of meteorite samples and the gamma-ray line observation. These radioactive nuclei, e.g.²²Na,²⁶Al,⁴⁴Ti and⁶⁰Fe bring about a drastic change in grain potential. Grains with larger radius than the critical radiusa _c attain a negative potential when grains are traversing a typical intercloud region.     

Liquid water on Mars: An energy balance climate model for CO2/H2O atmospheres

Geologic evidence of the prior existence of liquid water on Mars suggests surface temperatures T_s were once considerably warmer than at present; and that such a condition may have arisen from a larger atmospheric greenhouse. Here we develop a simple climate model for a CO₂/H₂O Mars atmosphere including water vapor-longwave opacity feedback in the atmosphere and temperature-albedo feedback at surface icecaps, under the assumption that once the Martian surface pressure was p_s ≥ 1 atm CO₂. Longwave flux to space is computed as a function of T_s and p_s using band-absorption models for the effect of the 15-μm fundamental, and the 10- and 15-μm hot bands, of the CO₂ molecule; as well as the pure rotation bands and e continuum of H₂O. The derived global radiative balance predicts a global mean surface temperature of 283°K at 1 atm CO₂. When the emission model is coupled to a latitudinally resolved energy balance climate model, including the effect of poleward heat transfer by atmospheric baroclinic eddies, the solutions vary, depending on p_s. We considered two cases: (1) the present Mars (p_s ? 0.007 atm) with pressure-buffering by solid CO₂ icecaps, and limited poleward heat flux by the atmosphere; and (2) a hypothetical “hot Mars” (p_s ? 1.0 atm), whose much higher CO₂ amount augmented by H₂O evaporative feedback yields a theoretical T_s distribution with latitude admitting liquid water over 95% of the surface, water icecaps at the poles, and a diminished equator-to-pole temperature gradient relative to the present.     

Determination of the electromagnetic field produced by a magnetic oblique-rotator

The inertial effect on the structure of the magnetosphere of a rotating star is investigated, in the corotation approximation for a surrounding quasi-neutral plasma. The equation of motion reduces to a usual static balance equation between the electromagnetic and the centrifugal forces, in the rotating frame. However the MHD condition, which can be regarded as a special form of the generalized Ohm's law, is modified by the inclusion of inertial effect, with a violation of the frozen-in condition in case of a general (i.e., not restricted to corotation) plasma motion. The inertial effect on the electromagnetic field is summarized in a partial scalar potential named the non-Backus potential, which is proportional to the centrifugal potential in the corotation approximation.An approximate solution of this corotation problem is given, in which another characteristic radiusr _M appears besides the light radiusr _L . This radius defines a distance beyond which the inertial effect becomes dominant over the electromagnetic one, and is useful in estimating the magnitude of the terminal velocity of a centrifugal wind. A few examples of the modification of dipole magnetic field due to the inertial effect are visualized. In an oblique-rotation case, it can be seen that such a warp of the neutral sheet (the surface ofB _r =0) is reproduced as observed in the Jovian magnetosphere.     

Emden-chandrasekhar axisymmetric,rigidly rotating polytropes

We determine equilibrium configuration of Emden-Chandrasekhar axisymmetric, solid-body rotating polytropes, defined as EC polytropes, for polytropic indices ranging from 0 (homogeneous bodies) to 5 (Roche-type bodies). To this aim, we improve Chandrasekhar's method to determine equilibrium configurations on two respects: namely, (a) no distinction exists between undistorted and distorted terms in the expression of the potential, and (b) the comparison between the expressions of gravitational potential and its first derivatives inside and outside the body has to be made on the boundary of a sphere of radius Ξ_E, which does not necessarily coincide with the undistorted Emden's sphere of radius \(\bar \xi _0 \geqslant \Xi _{\text{E}} \) . We also allow different values of \(\bar \xi _0 \) for different physical parameters, and choose a special set which best fits more refined results (involving more complicated and more expensive computer codes) by James (1964). We find an increasing agreement with increasing values of polytropic indexn and vice-versa, while a large discrepancy arises for 0≤n<1, which makes the approximations used here too much rough tobe accepted in this range. A real slight non-monotonic trend is exhibited by axial rations and masses related to rotational equilibrium configurations — i.e., when gravity at the equator is balanced by centrifugal force-with extremum points for 4.8<n<4.85 in both cases. The same holds for masses related to spherical configurations, as already pointed out by Seidov and Kuzakhmedov (1978). Finally, it is shown that isotrophic, one-component models of this paper might provide the required correlation between the ratio of a typical rotation velocity to a typical peculiar velocity and the ellipticity, for about \(\tfrac{3}{4}\) of elliptical systems for which observations are available.     

The temperature of nonspherical circumstellar dust grains

The temperatures of prolate and oblate spheroidal dust grains in the envelopes of stars of various spectral types are calculated. Homogeneous particles with aspect ratios a/b≤10 composed of amorphous carbon, iron, dirty ice, various silicates, and other materials are considered. The temperatures of spherical and spheroidal particles were found to vary similarly with particle size, distance to the star, and stellar temperature. The temperature ratio T _d(spheroid)/T _d(sphere) depends most strongly on the grain chemical composition and shape. Spheroidal grains are generally colder than spherical particles of the same volume; only iron spheroids can be slightly hotter than iron spheres. At a/b≈2, the temperature differences do not exceed 10%. If a/b≥4, the temperatures can differ by 30–40%. For a fixed dust mass in the medium, the fluxes at wavelengths λ≥100 are higher if the grains are nonspherical, which gives overestimated dust masses from millimeter observations. The effect of grain shape should also be taken into account when modeling Galactic-dust emission properties, which are calculated when searching for fluctuations of the cosmic microwave background radiation in its Wien wing.     

Meridional drift in the large-scale solar magnetic field pattern

A method of two-dimensional correlation functions has been applied to a sequence of synoptic maps of the large-scale magnetic field to obtain the meridional drift pattern of field structures. The meridional drift profile obtained is antisymmetric about the equator. The meridional drift is directed from the equator to the poles at latitudes below 45°. A maximum drift velocity of 11–13 m s^–1 is attained in the latitude range 30°. A picture of the space-time distribution of meridional drift is also obtained, which may be interpreted as resulting from the effect of azimuthal convective rolls (3 rolls per hemisphere) on the large-scale magnetic field. Rolls originate at high latitudes following the cycle maximum, and migrate equatorwards until the minimum of the next cycle. The picture in the equatorial region can correspond to convective rolls with lifetimes of about two years, or to the process of interaction of rolls from two hemispheres.     

Lunar surface potential and electric field

The Moon has no significant atmosphere, thus its surface is exposed to solar ultraviolet radiation and the solar wind. Photoemission and collection of the solar wind electrons and ions may result in lunar surface charging. On the dayside, the surface potential is mainly determined by photoelectrons, modulated by the solar wind;while the nightside surface potential is a function of the plasma distribution in the lunar wake. Taking the plasma observations in the lunar environment as inputs, the global potential distribution is calculated according to the plasma sheath theory, assuming Maxwellian distributions for the surface emitted photoelectrons and the solar wind electrons. Results show that the lunar surface potential and sheath scale length change versus the solar zenith angle, which implies that the electric field has a horizontal component in addition to the vertical one. By differentiating the potential vertically and horizontally, we obtain the global electric field. It is found that the vertical electric field component is strongest at the subsolar point,which has a magnitude of 1 V m-1. The horizontal component is much weaker, and mainly appears near the terminator and on the nightside, with a magnitude of several mV m-1. The horizontal electric field component on the nightside is rotationally symmetric around the wake axis and is strongly determined by the plasma parameters in the lunar wake.     

On the propagation of the electron streams generating type III bursts

The suggestion is explored that the two-stream instability has little effect on the propagation of the electron streams which generate type III bursts because the time required (ti) for development of the instability is comparable with or greater than the time available (Δt) for growth of the waves. Inferred parameters for streams in the corona and measured parameters for streams at the orbit of the Earth are compatible with this suggestion. Quasi-linear relaxation, which should occur as the stream forms, ensures that equality ti = Δt is set up initially, and restricts the number of escaping electrons to N _s ≈ 10³¹. The minimum density requirement on the stream for the two-stream instability to occur is found to be much less restrictive than the requirement that there should be many streaming electrons per Debye sphere.     

Spherical Magnetic Vortex in an External Potential Field: A Dissipative Contraction

We consider the dissipative evolution of a spherical magnetic vortex with a force-free internal structure, located in a resistive medium and held in equilibrium by the potential external field. The magnetic field inside the sphere is force-free (the model of Chandrasekhar in Proc. Natl. Acad. Sci. 42, 1, 1956). Topologically, it is a set of magnetic toroids enclosed in spherical layers. A new exact MHD solution has been derived, describing a slow, uniform, radial compression of a magnetic spheroid under the pressure of an ambient field, when the plasma density and pressure are growing inside it. There is no dissipation in the potential field outside the sphere, but inside the sphere, where the current density can be high enough, the magnetic energy is continuously converted into heat. Joule dissipation lowers the magnetic pressure inside the sphere, which balances the pressure of the ambient field. This results in radial contraction of the magnetic sphere with a speed defined by the conductivity of the plasma and the characteristic spatial scale of the magnetic field inside the sphere. Formally, the sphere shrinks to zero within a finite time interval (magnetic collapse). The time of compression can be relatively small, within a day, even for a sphere with a radius of about 1 Mm, if the magnetic helicity trapped initially in the sphere (which is proportional to the number of magnetic toroids in the sphere) is quite large. The magnetic system is open along its axis of symmetry. On this axis, the magnetic and electric fields are strictly radial and sign-variable along the radius, so the plasma will be ejected along the axis of magnetic sphere outwards in both directions (as jets) at a rate much higher than the diffusive one, and the charged particles will be accelerated unevenly, in spurts, creating quasi-regular X-ray spikes. The applications of the solution to solar flares are discussed.     

Kinematics and Flare Properties of Radio-Loud CMEs

A detailed analysis of the characteristics of coronal mass ejections (CMEs) and flares associated with decameter-hectometer wavelength type-II radio bursts (hereafter DH-type-II radio bursts, DH-CMEs or radio-loud CMEs) observed in the period 1997??C?2008 is presented. A sample of 61 limb events is divided into two populations based on the residual acceleration: accelerating CMEs (a _r>0) and decelerating CMEs (a _r<0). We found that average speed (residual acceleration) of all limb DH-CMEs (called radio-loud CMEs) is nearly three (two) times greater than the average speed of the general population CMEs (radio-quiet CMEs). While the initial acceleration (a _i) of the accelerating DH-CMEs is smaller than that of decelerating DH-CMEs (0.79 and 1.62 km?s^?2, respectively), the average speed and magnitude of residual acceleration of the accelerating and decelerating DH-CMEs are similar (??V _CME??: 1254 km?s^?1 and 1303 km?s^?1; ??a _r??: 0.026 km?s^?2 and 0.028 km?s^?2, respectively). The accelerating DH-CMEs attain their peak speed at larger heights than decelerating DH-CMEs. A good positive and negative linear correlation for accelerating and decelerating DH-CMEs (R _a=0.74 and R _d=?0.77, respectively) is found. The flares associated with accelerating DH-CME events have longer rise times and decay times than flares of decelerating DH-CME. The accelerating and decelerating DH-CMEs events associated with DH-type-II bursts have similar ending frequencies. The analysis of time lags between DH-type-II start and the flare onset shows that the delays are longer in accelerating DH-CMEs than decelerating DH-CMEs (P??7 %). However, the time lags between the DH-type-II start and the CMEs onset are similar.     

Solar wind access to the plasma sheet along the flanks of the magnetotail

Low-energy particle trajectories in an idealized magnetotail magnetic field are investigated to determine the accessibility of magnetosheath protons and electrons to the plasma sheet along the flanks of the tail magnetopause. The drift motion of the positively (negatively) charged particles incident on the dawn (dusk) magnetotail flank causes such particles to penetrate deeper into the magnetotail. For certain combinations of particle energy, incident velocity vector and initial penetration point on the tail magnetopause, the incident particles can become trapped in the plasma sheet, after which their net drift motion then provides a current capable of supporting the entire observed magnetotail field. The results further indicate that the bulk of the solar wind plasma just outside the distant tail boundary, which streams preferentially in a direction along the magnetopause away from the Earth at velocities around 400 km s^?1, can be caught up in the tail if the initial penetration point is within about 2R_E, of the quasi-neutral sheet. It is suggested that a large fraction of the magnetotail plasma is composed of former solar wind particles which have penetrated the magnetospheric boundary at the tail flanks.     

A class of new solutions of generalized charged analogues of Buchdahl’s type super-dense star

The present paper reports a class of new solutions of charged fluid spheres expressed by a space time with its hypersurfaces t=const. as spheroid for the case 0<K<1 with surface density 2×10¹⁴ gm/cm³. When the Buchdahl’s type fluid spheres are electrified with generalized charged intensity and it is utilized to construct a super-dense star and found that star satisfies all reality conditions except the casual condition for 0<K≤0.05. The maximum mass occupied and the corresponding radius have been obtained 8.130871 M _Θ and 24.60916 km respectively. Further, the redshift at the centre and on the surface are noted by z ₀=0.933729 and z _a =0.383808 respectively.     

Sheath effects on DEMETER ion drift measurements

The “Instrument d’Analyse du Plasma” on DEMETER includes an ion drift meter used to measure the direction of the incoming ram plasma ( [Berthelier et al., 2006a] and [Berthelier et al., 2006b]). Given the velocity of the satellite, and expected flow velocities of plasma along DEMETER's orbit, it is estimated that at mid latitudes, the direction of incident plasma as measured by IAP should be within approximately 2° of the ram direction. Yet, significantly larger angular deviations are measured routinely. An important assumption made in the interpretation of onboard instruments, such as IAP, is that neither the spacecraft nor the instrument significantly perturb the plasma that is being measured. In view of the large observed angular deviations, this paper examines the possible effect of the electrostatic sheath surrounding IAP. This is done with the 3D PIC simulation code PTetra. The model uses a full 3D particle in cell code with unstructured tetrahedral mesh capable of accurately representing the satellite geometry. The mesh is also adaptive so as to provide a fine spatial resolution in the vicinity of the particle sensor where it is needed, and a coarse resolution in regions where plasma parameters vary over a longer scale length. Calculation results show that while particle deflection associated with the electrostatic sheath near IAP can account for appreciable angular deflections for representative ionospheric plasmas, they are typically smaller than the ones observed. Additionally, the model is unable to reproduce the latitudinal dependence of the observed large deflection angles. It is concluded that sheath effects may cause appreciable distortions on the IAP type of ion flow meter instruments, and on other particle sensors in general. The larger observed deviations and their latitudinal dependence, however, must be attributable to other physical processes not accounted for in the model.     

Interactions of plasmas with magnetic field boundaries

The magnetopause, the boundary layer, or current sheath, which separates the magnetosphere from the solar wind, is the particular interaction considered in this paper.The collision free electron skin depth, $\text{ξ}{}_{\mathrm{e}}\text{=}\text{c}\text{ω}{}_{\mathrm{pe}}$, where c is the velocity of light and ω_pe, is the plasma frequency, gives a classical measure of the penetration depth of a collisionless plasma by an electromagnetic field. This penetration depth is small compared with the dimensions of the magnetosphere and hence the boundary layer may be conveniently considered in one dimension.In General all one dimensional solutions lie within an order of magnitude of the value of ξ_e, the only exception being the important one, in which the electric field perpendicular to the current sheath plane is not present, either due to a particular trapped particle distribution or due to a short circuiting end effect. For this exception the thickness is increased by the factor ($\text{m}{}_{\mathrm{i}}\text{i/m}{}_{\mathrm{e}}\text{)}{}^{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$.The current sheath solutions discussed are equilibrium solutions but not necessarily stable equilibrium solutions.The extension of the models to three dimensions has a larger effect than might at first be expected. The effect may be intuitively understood as a consequence of flux conservation in the sheath. The one dimensional solutions then correspond to the current sheath profiles at the thinnest point of the three dimensional sheath.     

Electron-positron and photon wind from the surface of a strange star

We consider the problem of strange-star (SS) radiation. The bare quark SS surface and electrons on the stellar surface generate an electric field that is strong enough for electron-positron pairs to be produced from a vacuum at a nonzero temperature. The luminosity in pairs is assumed to be within ?10⁴⁹ erg s^?1 from a surface with a characteristic radius of 10 km. We consider the energy transfer from pairs to photons by taking into account the well-studied reactions between e, e ⁺, γ and obtain a change in the photon spectrum with luminosity. Our analysis is restricted to the spherically symmetric case. The magnetic field is disregarded. To solve the problem, we developed a new numerical method of integrating the Boltzmann kinetic equations for pairs and photons. This method is used to calculate the problem up to a luminosity of 10⁴² erg s^?1 This region is difficult to investigate when the optical path for pairs or photons is considerably larger than unity but the two optical depths are not simultaneously much larger than unity (when hydrodynamics with heat conduction is applicable). It turns out that the mean photon energy is approximately equal to $\bar \in _\gamma \approx m_e c^2$ (the annihilation line for pairs) at a modest luminosity, L?1×10³⁷ erg s^?1, and decreases to ≈210 keV at L?10³⁸ erg s^?1. Hydrodynamic estimates point to an increase in the mean energy $\bar \in _\gamma$ to 1 MeV as the luminosity further increases to L?10⁴⁹ erg s^?1. Our calculations may prove to be useful in interpreting soft gamma repeaters (SGRs) and are of methodological interest.     

Modulational instability of fast magnetosonic waves in a solar plasma

Transverse amplitude modulations of fast magnetosonic waves propagating perpendicular to the background magnetic field are shown to be unstable on a time scale τ ～- λ_∥/V _aφ, if the wave amplitude φ exceeds a critical value, φ _c = C _s/V _a. The slow modes generated by the modulational instability under gravity can propagate along the magnetic field with the characteristic velocity, V _ph = g/2k _∥ V _aφ. The applications of this modulational instability and slow-mode generation mechanism to a solar plasma are discussed.