ULF Waves Associated with Solar Wind Deceleration in the Earth＇s Foreshock

Characteristics of ULF waves associated with the solar wind deceleration in the Earth＇s foreshock on 6-7 April 2003 is studied using the wave telescope technique. In the satellite frame, the ULF waves are the left-handed polarized and quasi anti-parallel propagating mode, with a power peak at about 18.63mHz. The wave vector in the GSE coordinates is estimated to be k = （-4.29, 2.28, 1.21）×10^-4 km^-1, In the solar wind frame, the frequency of waves becomes - 9.39 mHz after the Doppler shift correction. The propagation direction of the waves is thus reversed and correspondingly the polarization of the waves becomes right-handed. The above-mentioned characteristics of the ULF waves in the solar wind frame indicate that the ULF waves associated with the solar wind deceleration are the Alfven-whistler waves, which have been frequently reported in both the observations and computer simulations.     

Contribution from the Earth＇s Bow Shock to Region 1 Current under Low Alfven Mach Numbers

Using global MHD simulations of the solar wind-magnetosphere-ionosphere system, we investigate the dependence of the contribution from the Earth＇s bow shock （I1bs） to ionospheric region 1 field aligned current （FAC） （I1）. R is found that Ilbs increases with increasing southward interplanetary magnetic field （IMF） strength Bs, if the AIfven Mach number MA of the solar wind exceeds 2, a similar result as obtained by previous authors. However, if MA becomes close to or falls below 2, I1ba will decrease with Bs in both magnitude and percentage （i.e., I1bs/I1） because of the resultant reduction of the bow shock strength. Both the surface current density Jbs at the nose of the bow shock and the total bow shock current Ibs share nearly the same relationship with MA, and vary non-monotonically with MA or Bs. The maximum point is found to be located at MA = 2.7. Three conclusions are then made as follows： （1） The surface current density at the nose, which is much easier to be evaluated, may be used to largely describe the behaviour of the bow shock instead of the total bow shock current. （2） The peak of the total bow shock current is reached at about MA = 2.7 when only Bs is adjusted. （3） The non-monotonic variation of the bow shock current with MA causes a similar variation of its contribution to region 1 FAC. The turning point [or such contribution is found to be nearly MA = 2. The implication of these conclusions to the saturation of the ionospheric transpolar potential is briefly discussed.     

Determination of convergence intervals of the series solutions of Emden-Fowler equations using polytropes and isothermal spheres

We consider the Emden-Fowler type of equations. We construct a recurrence relation for the components of the approximate solution and investigate the convergence conditions. The previous results on the convergence radius of the series solution have been improved.     

Enhancement of the guide field during the current sheet formation in the three-dimensional magnetic configuration with an X line

Results are presented from studies of the formation of current sheets during exciting a current aligned with the X line of the 3D magnetic configuration, in the CS-3D device. Enhancement of the guide field (parallel to the X line) was directly observed for the first time, on the basis of magnetic measurements. After the current sheet formation, the guide field inside the sheet exceeds its initial value, as well as the field outside. It is convincingly demonstrated that an enhancement of the guide field is due to its transportation by plasma flows on the early stage of the sheet formation. The in-plane plasma currents, which produce the excess guide field, are comparable to the total current along the X line that initiates the sheet itself.     

Magneto-Hydrodynamic High-n Ballooning Mode Instability of an Analytic Axi-Symmetric Toroidal Equilibrium with Arbitrary Aspect Ratio

An exact ballooning mode eigen-equation is derived to study stability of axi-symmetric toroidal plasma with arbitrary aspect ratio, including the tokamak, the finite aspect ratio and the spherical torus plasmas. For comparison with the widely used （ s-α） model, an analytic exact equilibrium configuration with circular magnetic surfaces is analysed in detail. It is indicated that the （s - α） model needs to be improved for more realistic configurations.     

On the scarcity of solutions of the equations of magnetohydrodynamic equilibria with flow

While particular analytic solutions to the equations of axisymmetric MHD equilibria with flow are known, it is not clear what possible choosing of the free parameters of the equation of the magnetic flux will yield a solution. The most important of these is the poloidal stream function. We show that for a given flow to be able to yield an equilibrium, the flow itself must satisfy an analogous equation to the generalized Grad-Shafranov one. The problem therefore turns out to be how common are solutions to this type of equations. It is shown that in a natural space of functions, the set of these solutions is contained within a manifold of infinite codimension: extremely small by any criteria. Hence the class of flows for which an equilibrium, even defined only locally and irrespective of boundary conditions, may be found, is highly constrained.     

Dual equilibrium in a finite aspect ratio tokamak

A new approach to high pressure magnetically-confined plasmas is necessary to design efficient fusion devices. This Letter presents a new sort of equilibrium combining two solutions of the Grad-Shafranov equation, which describes the magnetohydrodynamic equilibrium in toroidal geometry. The outer equilibrium is paramagnetic and confines the inner equilibrium, whose strong diamagnetism permits to balance large pressure gradients. The existence of both equilibria in the same volume yields a dual equilibrium structure. This combination improves free-boundary mode stability.     

Anti-gravitation

The possibility of a symmetry between gravitating and anti-gravitating particles is examined. The properties of the anti-gravitating fields are defined by their behavior under general diffeomorphisms. The equations of motion and the conserved canonical currents are derived, and it is shown that the kinetic energy remains positive whereas the new fields can make a negative contribution to the source term of Einstein's field equations. The interaction between the two types of fields is naturally suppressed by the Planck scale.     

Out-of-plane bipolar and quadrupolar magnetic fields generated by shear flows in two-dimensional resistive reconnection

Shear flows perpendicular to the anti-parallel reconnecting magnetic field are often observed in magnetosphere and interplanetary plasmas, and in laboratory plasmas toroidal differential rotations can also be generated in magnetic confinement devices. Our study finds that such shear flows can generate bipolar or quadrupolar out-of-plane magnetic field perturbations in a two-dimensional resistive MHD reconnection without the Hall effects. The quadrupolar structure has otherwise been thought a typical Hall MHD reconnection feature caused by the in-plane electron convection. The results will challenge the conventional understanding and satellite observations of the signature of reconnection evidences in space plasmas.     

Mechanism of neoclassical tearing modes triggering by a magnetic perturbation

A new mechanism whereby Neoclassical Tearing Modes (NTMs) can be triggered through toroidal mode coupling to a magnetic perturbation is proposed. The physical picture is the presence of a relatively small “pre-NTM” magnetic island whose frequency is modified by the perturbation, changing polarization current effects from stabilizing to destabilizing.     

Analytical properties and exact solutions of static plasma equilibrium systems in three dimensions

For static reductions of isotropic and anisotropic magnetohydrodynamics plasma equilibrium models, a complete classification of admitted point symmetries and conservation laws up to first order is presented. It is shown that the symmetry algebra for the isotropic equations is finite-dimensional, whereas anisotropic equations admit infinite symmetries depending on a free function defined on the set of magnetic surfaces. A direct transformation is established between isotropic and anisotropic equations, which provides an efficient way of constructing new exact anisotropic solutions. In particular, axially and helically symmetric anisotropic plasma equilibria arise from classical Grad-Shafranov and JFKO equations.