Plasma jet dynamics in the magnetosphere

 

I.M. Podgorny, A.I. Podgorny (Lebedev Institute of Physics RAN, Moscow 117924,Russia, Institute for Astronomy RAN, Moscow, 109017, Russia)

 

Plasma jet interaction with the magnetosphere is considered in 3D MHD approximation. The program PERESVET is used for numerical solution the system of equations with all dissipative terms for compressible plasma. At sub Alfvenic high beta jet injection across the magnetic field the magnetospheric magnetic field is expelled, and magnetic cavity appears. Such field configuration prevents the radial expansion of plasma. The system of field-aligned currents appears which involves magnetospheric plasma into motion. Field-aligned current production initiates field lines twisting, and plasma velocity curls generation Field-aligned currents propagate along the field lines with the Alfvenic velocity. The jet deceleration is determined by the momentum transfer to the magnetospheric plasma.

At super Alfvenic jet injection across the magnetic field the field lines envelope the jet, and energy accumulation in a current sheet occurs. At high density jet injection along the magnetic field the magnetic field configuration of an adiabatic trap is created. This trap is stable because its magnetic field increases toward periphery. Ahead of the jet in this case the wave of rarefaction is established which propagate with the jet velocity. The jet motion at angels from 0 to 90 degrees is also considered.

The results are presented for long jets and restricted plasmoids. Obtained data permit to predict jet behaviour in the magnetosphere including results of active experiments performed in different conditions. Some preliminary results has been published in [1, 2].

1. A.I. Podgorny and I.M. Podgorny. Cosmic Research 35, 39 (1997).

2. A.I. Podgorny and I.M. Podgorny. Cosmic Research 35, 253 (1997).

 

 

Electrodynamics of rotating planetary plasmaspheres in dipole magnetic field

 

Yu.V. Chugunov (Institute of Applied Physics RAS, Nizhny Novgorod, Russia)

 

As a model of the real structure of the planetary plasmasphere, the electrodynamic problem of the planet with dipole magnetic field corotating with the plasma envelope is considered. The structure of the plasma envelope is defined by conductivity and angular velocity of magnetospheric plasma as functions of the distance r from the planetary center and the angle counted off the rotation axis. The exact solution to the Maxwell equations is obtained in considered axisymmetric case, when rotational and magnetic axes coincide, within the framework of unipole electrodynamics. These solutions describe possible distributions of electric fields, currents and charges in the rotating plasma envelope surrounding magnetized planet. As an example, under the proposed theory it is obtained the solution corresponding to following structure of plasmasphere: 1) the plasmasphere corotating with the planet and located between L-shells from L = 1 to L = L_; 2) the polar region with differential spherically symmetrical rotation and located from r = R to r = R + R_ , R - is a planetary radius, 0 < R_ - R << R ; 3) the transitional region of the plasmasphere rotating differentially with the angular velocity depending on the L-number and located within L-shells from L = L_ to L = L_ + gL_, q << 1; 4) the external (vacuum) region. It is shown that in this model the electric field potential is equal to zero in the external region (L > L_ + qL_) independently on the numbers of the boundary L-shells. These solutions permit to construct the planetary plasma flows of plasmasphere type as well as plasmapause one.

The work is done under support of a grant RFFR # 96-02-16471a.

 

 

MHD flow of ideal anisotropic plasma around a sphere:

model for the magnetosheath

 

A.A. Samsonov, M.I. Pudovkin (Institute of Physics, University of St.Peterburg, St.Peterburg 198904, Russia)

 

The numerical results of the MHD flow of ideal anisotropic plasma around a sphere are presented. This model describes the flow in the magnetosheath. The comparison of the double adiabatic and double polytropic models with experimental data are given. The double adiabatic model is shown to give acceptable description of the flow if the diffusive terms are included.

 

 

Energeetic particle acceleration in a magnetospheric strong turbulent plasma

 

P.A. Bespalov (Institute of Applied Physics RAS, 46 Ulyanov st., 603600 Nizhny Novgorod, Russia)

V.G. Misonova (State University, 23 Gagarin st., 603600 Nizhny Novgorod, Russia)

 

The problem of energetic particle acceleration in strongly turbulent plasma is considered. The model of successive condensers with oscillating on plasma frequency electric field and casual jumps of oscillation phase is employed. For different relations between statistical characteristics of model and particle velocity the diffusion coefficients in velocity space are calculated. The solutions of diffusive equations in stationary and spatially homogeneous cases are presented. The average energy of accelerating particles are estimated. The estimation of average energy shows that particles can be effectively accelerated by the system of condensers. The acceleration is more effective in cases of more strong space and temporal correlation between the successive jumps of the oscillating phase of the condensers. The peculiarities of relativistic particle acceleration are analyzed. Received results are useful for investigations of particle acceleration processes in high latitude magnetospheric regions with strong plasma turbulence.

Acknowledgments. This work is supported by the Russian Foundation of Fundamental Researches grant No.98-02-16236.

 

 

Large plasma device for modeling space phenomena

 

A.V. Kostrov, A.V. Strikovsky

(Institute of Applied Physics RAS, Ulyanov st., 46, 603600 Nizhny Novgorod, Russia)

 

In connection with intensive investigations of near Earth and far space of principle significance getting possibility modelling some space phenomena in laboratory condition. Institute of Applied Physics have large experimental device allowing produce magnetoactive plasmas. The main direction in real time is investigation of interaction and propagation of intense whistler range waves with magnetoplasma (WH _w0 <<wHe <wpe), where WH is lower-hybrid frequency, w0 is wave frequency, wHe and wpe are plasma and cyclotron frequency respectively. A large plasma device "КРОТ" for experiments of wave-plasma interactions in large magnetized plasma consists of the following:

A solenoidal current-carrying (1.5 m in diameter, 3.5 m long) to provide the pulsed magnetic mirror (mirror ratio = 2, B < 1000G, t = 20 msec) is situated inside a vacuum chamber (3 m in diameter, 10 m long). The trapped plasma is produced by a pulsed inductive rf-discharge. To get uniform axial plasma profile, six current loops (1.2 m in diameter) placed in the magnetic mirror and fed with three rf-power supply 1 MW each are used (t ~ 1 msec, f = 5 Mhz). Most measurements are being obtained in the afterglow plasma (e-folding decay time~1.5 msec, Nmax = 1012cm-3, Te < 10eV), while electrons have collisionally relaxed to the thermal equilibrium with ions Ti = 0.5eV. The radial density profile is close to parabolic one.

The large size of our laboratory magnetized plasma gives the possibility to study propagation of unbounded waves in detail. For example whistler wave-particle interaction indispensable for an understanding of the triggering mechanisms, para-metric instability whistler waves near the lower hybrid resonance level and so on.

 

 

Plasma filamentation: theory and modeling

 

A.S. Savjolov, S.K. Zhdanov, K.N. Korotaev, V.M. Smirnov

(Moscow State Engineering and Physics Institute.115409 Moscow, Russia)

 

Plasma filamentation can strongly influence charged particles density and magnetic field distributions for different astrophysical objects including cosmic jets and auroral spirals. We present recent theoretical results as well as results of the experimental modeling using pulsed discharge facility. The peculiarities of the analytical description, computational and experimental modeling of the charged particles currents in space are also discussed.

 

 

Вязкое трение в ламинарных и турбулентных гидродинамических течениях

 

И.В. Мингалев, О.В. Мингалев, В.С. Мингалев (Полярный геофизический институт, Апатиты)

 

При математическом моделировании динамики верхней атмосферы широко применяются уравнения Навье-Стокса, справедливые для так называемой ньютоновской жидкости, в которой компоненты тензора вязких напряжений прямо пропорциональны градиентам компонент скорости течения среды, а коэффициентом пропорциональности является динамический коэффициент вязкости, не зависящий от поля скорости. Поэтому в ньютоновской жидкости при неограниченном возрастании градиента скорости вязкие напряжения должны также неограниченно возрастать, что противоречит экспериментальным данным по обтеканию твердых поверхностей высокоскоростными потоками. Следовательно, модель ньютоновской жидкости, которая очень хорошо описывает течения с малыми градиентами скорости, не применима для описания течений с большими градиентами скорости, что является типичной ситуацией для верхней атмосферы. Поэтому весьма актуальным является установление такого закона вязкого трения, который был бы справедлив для течений не только с малыми, но и с большими градиентами скорости, а такие течения, как известно, стремятся перейти из ламинарного режима в турбулентный.

В настоящей работе предпринимается попытка установить закон вязкого трения в ламинарных и турбулентных гидродинамических течениях, допускающих произвольные по величине градиенты компонент скорости. Этот закон ищется в классе так называемых обобщенных ньютоновских моделей, в которых коэффициент пропорциональности может зависеть от поля скорости, и его называют кажущейся вискозиметрической вязкостью (КВВ). В работе предложен новый общий метод для нахождения КВВ, основанный на использовании экспериментальных данных о профилях скорости и кажущейся вязкости в течениях сплошной среды по круглым трубам постоянного сечения. При помощи этого метода по опубликованным экспериментальным данным о течениях воды по круглым трубам нами установлен как качественный вид КВВ, так и построена количественная модель КВВ, которая может быть использована при математическом моделировании ламинарных и турбулентных течений, базирующемся на применении обобщенных уравнений Навье-Стокса для описания динамики сплошной среды.

 

 

Стационарные вихревые течения идеальной плазмы, допускаемые условием "магнитостатического равновесия"

 

В.П. Козелов (Полярный геофизический институт КНЦ РАН, Апатиты)

 

Условие "магнитостатического равновесия" сÑ p=[j´ B] рассмотрено в контексте полной системы стационарных МГД- уравнений для идеальной баротропной плазмы. Показано, что существуют нетривиальные решения с ненулевой скоростью и завихрённостью течения, в которых j ~ rot v, а плотность и давление могут изменяться только вдоль траекторий стационарного течения по вполне определённому закону. Найдены условия, ограничивающие возможные геометрические конфигурации таких течений. Дана явная формула для продольного тока.