Solitary autowaves in magnetic flux tubes

The weakly nonlinear dynamics of surface magnetoacoustic waves in magnetic flux tubes in the presence of the effects of dissipation and active non-adiabaticity is considered. The wave is described either by the extended Benjamin-Ono equation (slab geometry) or by the extended Leibovich-Roberts equation (cylindrical geometry). For the slab geometry, it is shown that solitary waves with arbitrary initial parameters evolve to solitons with specific amplitude, length and speed defined by the physical parameters of the magnetic slab.     

Rossby waves in the magnetic fluid dynamics of a rotating plasma in the shallow-water approximation

We have studied rotating magnetohydrodynamic flows of a thin layer of astrophysical plasma with a free boundary in the β-plane. Nonlinear interactions of the Rossby waves have been analyzed in the shallow-water approximation based on the averaging of the initial equations of the magnetic fluid dynamics of the plasma over the depth. The shallow-water magnetohydrodynamic equations have been generalized to the case of a plasma layer in an external vertical magnetic field. We have considered two types of the flow, viz., the flow in an external vertical magnetic field and the flow in the presence of a horizontal magnetic field. Qualitative analysis of the dispersion curves shows the presence of three-wave nonlinear interactions of the magnetic Rossby waves in both cases. In the particular case of zero external magnetic field, the wave dynamics in the layer of a plasma is analogous to the wave dynamics in a neutral fluid. The asymptotic method of multiscale expansions has been used for deriving the nonlinear equations of interaction in an external vertical magnetic field for slowly varying amplitudes, which describe three-wave interactions in a vertical external magnetic field as well as three-wave interactions of waves in a horizontal magnetic field. It is shown that decay instabilities and parametric wave amplification mechanisms exist in each case under investigation. The instability increments and the parametric gain coefficients have been determined for the relevant processes.     

Internal dynamics of a plasma propelled across a magnetic field

When a plasma is pushed across a magnetic field by some nonelectromagnetic force, ions and electrons get turned in opposite directions by the magnetic field. This creates an internal current as well as sheaths at the plasma surfaces and results in an electric field which allows the plasma to maintain some, or even most of its initial momentum in the form of E&oarr;×B&oarr; drift. An exact analysis of that process is presented for the internal region of the plasma. The energy provided by the initial push is used, in part, to create some gyrations inside the plasma. When the rest energy density of the plasma exceeds twice the magnetic energy density (or when the Alfven speed is less than c), there will be enough energy to spare for the plasma to continue across the magnetic field at half its initial momentum. Two cases are considered: an impulsive start and a gentle push such as provided by gravity. The amplitude of the resulting internal gyrations becomes small in the second case. The frequencies of the gyrations are those of extraordinary modes of very long spatial wavelength     

Universality in solar flare, magnetic storm and earthquake dynamics using Tsallis statistical mechanics

The universal character of the dynamics of various extreme phenomena is an outstanding scientific challenge. We show that X-ray flux and D_st time series during powerful solar flares and intense magnetic storms, respectively, obey a nonextensive energy distribution function for earthquake dynamics with similar values for the Tsallis entropic index q. Thus, evidence for universality in solar flares, magnetic storms and earthquakes arise naturally in the framework of Tsallis statistical mechanics. The observed similarity suggests a common approach to the interpretation of these diverse phenomena in terms of driving physical mechanisms that have the same character.     

On the containment of plasma in stationary magnetic and high-frequency fields I

The stationary state of a collisionless plasma in a magnetic mirror is analyzed provided that a strong h.f. field is present. The h.f. field frequency is somewhat higher than the electron cyclotron frequency. The pressure acting on the plasma and the height of the h.f. potential barrier are derived in particular. The h.f. potential yields the possibility of eliminating the loss cone in the velocities distribution. The upper limits, which the electron temperature must not exceed, are derived. If an appropriate stationary magnetic field is used, the required incident wave power can be diminished and the allowable electron temperature can be increased. Some new results concerning the case of a homogeneous magnetic field are presented.     

On the containment of plasma in stationary magnetic and high-frequency fields III

The lower limits are derived for the high-frequency field pressure which is necessary for elimination of the loss cone of a mirror vessel. The selfconsistent circularly polarized field is considered, the frequency being near to the cyclotron frequency of an electron or of an ion. The field pressure can be amplified by appropriately chosen dielectric slabs.The author is indebted to the participants of the meeting held at the Institute on 25 November 1969 for the review of the paper.     

On the containment of plasma in stationary magnetic and high-frequency fields II

The case is analysed when the ratio of the length of the magnetic mirror to the skin depth is arbitrary. It is shown that a certain diminishing of the required power of the incident wave can be achieved by an appropriate choice of the stationary magnetic field. The electron temperature must not be much higher than one electronvolt.The author is indebted to the participants of the seminar held at the Institute on 3 June 1969 for the review of the results presented here.     

On the nonlinear dynamics of the easy-plane antiferromagnetic chain in an external magnetic field

We present a theoretical investigation of soliton excitations in an easy-plane 1d antiferromagnet in an external magnetic field beyond the Sine-Gordon approximation. We find that there exist two types of solitons. One of them depends strongly on the magnetic field, becoming unstable at a critical magnetic field B_c. The other one is stable for all magnetic fields and can be described by a Sine-Gordon model. We discuss the relevance of these excitations for neutron scattering experiments.     

Creation of magnetic energy in the solar atmosphere

We show that a magnetic flux tube can grow in strength and size provided the temperature increases outward at the edge of the tube where the axial magnetic field declines to its external value. The radius of the tube increases at a rate determined by our theory. It is the coincidence of temperature and magnetic field gradients of opposite sign that generates the new field, and if this is lost the tube ceases to grow. The phenomenon is illustrated by adopting plausible distributions for the temperature and magnetic field strength, which yield an expression for the rate of growth of the magnetic field magnitude B. The mechanism provides a possible explanation of the fibrous nature of solar magnetic fields.     

Transverse dynamics of high-density relativistic electron beams propagating in plasma in the direction of the external magnetic field

Based on analysis of the effective potential, a possibility is found to realize a single type of radial evolution of high-density relativistic electron beams. This operating mode is characterized by periodic oscillations of the beam radius within a certain range. Conditions are found for radial beam stabilization under this beam transport regime.     

On the origin of soft x-ray and microwave sources of emission in solar magnetic loops

One possible mechanism is proposed for the appearance of high-temperature sources of emission in solar magnetic loops visible sometimes in the microwave and soft x-ray bands in active regions, even out of flares. The main concept of this mechanism is as follows. Due to the existence of current in the magnetic loop, there is a component of the electric field E which is longitudinal to the magnetic field. In this case, at some heights the parameters of solar atmospheric plasma (density and temperature) appear to cause a certain number of electrons to be in a runaway regime. These electrons can be accelerated to energies of about 1–2 keV. This corresponds to the temperature of the observed microwave and x-ray source. Accelerated electrons satisfying the trapping condition will gradually fill the magnetic tube, and after a while a hot x-ray loop can occur. Similar mechanisms of the appearance of hightemperature sources of emissions in active regions probably take place in the simple loop flare for the class of thermal flares visible in the microwave and soft x-ray bands.Department of Astrophysics and Cosmic Plasma Physics, Applied Physics Institute, Russian Academy of Sciences, Nizhnii Norgorod. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 37, No. 7, pp. 836–850, July, 1994.     

Open-type image tubes for plasma research

Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 55, No. 3, pp. 518–520, September, 1991.