Experimental demonstration of the “unipolar cell” dynamics in a large laboratory magnetoplasma

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The nonambipolar or “unipolar” particle transport accompanied by excitation of a system of eddy (short-circuit) currents can ensure the fast dynamics of small-scale magnetoplasma disturbances arising under pulsed localized rf heating, and evolving in electron magnetohydrodynamics regime of parameters. In this regime, redistribution of plasma density is possible, which is an order of magnitude faster than the classical mechanism of the ambipolar transport with the joint movement of electron-ion pairs. During the evolution of thermal plasma irregularity in the unipolar transport regime, magnetized electrons leave the heated plasma area along the magnetic field, while nonmagnetized ions drift predominantly across the field. The electric current arising in this case can be closed through the background plasma surrounding the irregularity. This regime can determine the times of development and decay of narrow field-aligned plasma density irregularities that arise, e.g., in the pulsed ionospheric heating experiments. The refined laboratory experiments with specially selected parameters, which were carried out in a large-scale Krot plasma device with localized (pointlike) short-pulse rf heating of electrons, demonstrated clearly the unipolar-cell dynamics. The “unipolar cell” is understood as a self-consistent, freely relaxing plasma-field structure, which is formed by the initial field-aligned plasma density depletion in a heated flux tube, the peripheral background plasma density enhancements and depletions, and a quadrupole system of electric eddy currents.