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No abstract available

[en] Plasma with natural, dropping to mirrors, pressure distribution is subjected to flute magnetohydrodynamical instability in simplest axisymmetric traps. A newly discovered example of a mirror device stable to large-scale flute perturbations points out existence of traps of this type where instability relatively to all the models is attained under connection with an element of opposite sign of force line curvature. A class of traps characterized by this property is described in the paper

[en] A new method for suppression of instabilities in a plasma by means of systems of automatic control has been developed. The possibility of applying this method for the stabilization of a continuous medium is associated with the fact that only a few modes of its oscillations are excited in reality, instead of the whole enormous number of its degrees of freedom. From the practical point of view the method is most appropriate for suppression of large-scale vibrations. Two mechanisms of stabilization are found. The external control system makes it possible to change the phase velocities of waves in a plasma and break its resonance interaction with particles and with each other. In this way strong instabilities with a large increment, in particular, hydromagnetic ones are suppressed. For the stabilization of dissipative instabilities with a small increment it is sufficient to use the external system for introducing additional attenuation into plasma oscillations. This has been confirmed by numerous experiments with drift waves

[en] The field of a static charge placed in an equilibrium plasma is screened at a distance of the order of the Debye radius. Debye screening occurs both with and without an external magnetic field. This property also persists when the plasma is not an equilibrium plasma but the velocity distribution function of the particles is isotropic (the screening radius in this case contains the characteristic value of the energy instead of the temperature). The situation can change if the distribution is anisotropic. First, the drop in the field can become non-Debye. In particular, in an unmagnetized plasma some distribution functions are characterized by a power-law decrease of the field. Second, a static test charge induces a magnetic as well as an electrostatic field in an anisotropic plasma. In this communication the authors describe the anomalies of screening of the field of a static charge in a magnetized plasma. For definiteness they consider a situation (typical, e.g., of magnetic mirror systems) when the ionic component is anisotropic. The simplifications for the sake of computations are limited to the case of a charge which extends along the magnetic field and only harmonics much longer than the Debye length are significant in the Fourier expansion of the density of this charge in the longitudinal coordinate

[en] It is shown the in stability, caused by the wall resistivity and specific for the plasma with β ∼ 1, stabilized by the wall relative to the MHD-mode, may be suppressed through the feedback system, controlled by the oscillation magnetic field. Several estimates are presented

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[en] The integral equation describing the z dependence of the trapped-particle instability perturbation potential var-phi(z) along a magnetic field line is solved numerically using the approximation that the magnetic field B(z) in the system is a piecewise-constant function. Examples are considered of a simple axisymmetric confinement system and systems consisting of a central axisymmetric configuration and end cells. Besides the well-known solution with a maximum value of var-phi(z) in the equatorial plane of an axisymmetric mirror, modes (having a smaller growth rate) are found with maxima in the region where the magnetic field increases near the mirrors. The eigenvalues (growth rates) as a function of the length of the central cell and the magnetic field in the external mirror, which determine the number of untrapped particles, are traces. 7 refs., 6 figs

[en] Experimental results on the feedback stabilisation of kink instability in the TO-1 tokamak are reported. The amplitude of the magnetic probe signal was observed to decrease or increase depending on the phase in the feedback system. The amplitude decrease was accompanied by a 20% reduction in the discharge voltage, an increase in the electron temperature from 200 to 300 eV and an increase in the plasma density from 0.6 to 0.9.10¹³ cm^-3. The feedback exerted a stabilising effect on the disruptive instability. The experimental results are explained using a simple theoretical model. (author)