Energization of plasma in a weak magnetic field and structure of the geomagnetic tail
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A ‘two-fluid’ plasma is described as a single continuum characterised by the generalised tensor of mechanical pressure and generalised vector of flow of mechanical energy. Plasma energization due to the transfer of mechanical energy inside the plasma body is emphasised and the energization of plasma by conversion of the electromagnetic energy into the mechanical energy is discussed. Two kinds of conversion associated with the convection electric field −(1/c)V×B and with the deviationE* of the total electric field from −(1/c)V×B are distinguished. TheV×B-field is related to the work done upon the plasma, while theE*-field is related to the plasma heating.
Plasma motions with scale length larger than the Debye distance, taking place in the central part of the Earth-plasma sheet, are considered. The change of energy of any element of plasma is due mainly to the transfer of mechanical energy across the element's boundary; the EM-field is not strong enough to make a significant contribution. The work done by the internal loads is the main source of mechanical energy in the configurations in which the physical quantities do not vary along the current lines. The rates of change of the kinetic and internal energies are comparable. The transfer of mechanical energy is the principal source of the kinetic energy also in the general case when the physical quantities vary along the current lines. Conversion of the EM energy into mechanical energy is the main source of the internal energy in this case. In the tail plasma located outside the central part of the plasma sheet, conversion of the EM-energy into mechanical energy, which is due to the work done by the EM-force, takes place. The tail plasma is likely to undergo a two-phase energization process: first, it is accelerated and later, when it approaches the ‘neutral’ sheet, it is heated.
KeywordsInternal Energy Physical Quantity Mechanical Energy Plasma Sheet Electromagnetic Energy
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