The authors consider the behaviour of the boundary of a plasma column in a strong, constant, inhomogeneous magnetic field and a high-frequency (HF) E-wave field. An azimuthal current is produced in the plasma by the HF-field. The direction of the azimuthal current depends on the direction of the constant, longitudinal magnetic field Hz. In all cases, however, this current causes the longitudinal magnetic field in the plasma to increase (paramagnetic effect). Stabilization is produced through compensation of the polarization currents by paramagnetic currents due to the HF-fields. The behaviour of the plasma column in a magnetic field of mirror-trap configuration was investigated experimentally. The high-frequency field was a rotating dipole, homogeneous along the constant magnetic field. The direction of the angular velocity vector for the HF-field coincided with the direction of the constant field.The studies showed that the behaviour of a plasma in a magnetic mirror trap depends largely on the curvature of the lines of force of the constant magnetic field. In the pinched regime, when the column-formation process has been completed, the level of the observed fluctuations increases with increasing curvature of the mirror-trap field. Tongue-shaped plasma streams are produced at the surface of the plasma column, perpendicular to the magnetic field. The “tongue” rotates in a direction which matches the rotation direction of the constant magnetic field. The frequency of the “tongue” rotation is in the range of 100–300 kHz. In addition to the intense deformation corresponding to the m = 1 mode, there are also other modes of higher orders. It is shown that the centrifugal effects caused by plasma rotation contribute to the instability.To control the rotation effect, use was made of a constant magnetic field of octupole configuration, which behaved in the same way as a high-frequency magnetic field rotating in the direction opposite to the plasma rotation.The experimental results provide sufficiently convincing evidence of the possibility of stabilizing convective-type instabilities arising in a plasma.

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The authors consider the equilibrium confinement of a toroidal plasma pinch in a static magnetic field and in a high-frequency large-amplitude field in the general case where the gas-kinetic plasma pressure NT is comparable with the pressure of the high-frequency field . It is assumed that the high-frequency field in the range of frequencies 1-10 MHz has a helical or multipole configuration and is excited by given external high-frequency currents passing through the current sheath surrounding the pinch.At high amplitudes of the high-frequency field, it is necessary to allow for the effect of the toroidicity of the system on the equilibrium conditions. In a first approximation with respect to the small parameters Δ/rp and rp/R (Δ is the displacement, rp is the radius of the pinch, R is the major radius of the torus) expressions are found for the high-frequency fields in a system with a displaced pinch and the condition for equilibrium of the pinch as a whole along the major radius is obtained. The equilibrium displacement of the pinch is determined from this condition, making use of the field values of the first approximation at the plasma boundary.It is shown that the use of high-frequency large-amplitude fields offers additional possibilities of controlling the equilibrium displacement. In particular, the effect of the toroidicity of the high-frequency field leads to the occurrence of an additional foree, which in a number of cases causes the pinch to be displaced to the inner wall of the toroidal chamber. When , it is also possible to have a paramagnetic effect when the pinch is forced out by a non-uniform static field towards the side where the intensity of the field is higher, i.e. to the inner wall of the torus. Under certain conditions the phenomena making positive or negative contributions to the equilibrium displacement of the pinch may be mutually compensating, so that the displacement can be made fairly small or even eliminated by suitable choice of the system parameters.The minimum displacement of the pinch for a given amplitude of the high-frequency current in the circuit practically always occurs in the case of quadrupole systems.It is shown that equilibrium confinement of plasma by high-frequency fields is also possible in systems where the plasma pinch is surrounded by a continuous conducting shell (so-called "high-frequency tokamak").The theoretical results obtained are in agreement with the results of experimental investigations.

The authors consider the interaction of a plasma column in a constant magnetic field H z with a system of two counter-rotating high-frequency magnetic fields whose axis of rotation is directed along a constant magnetic field. Both the first and the second wave are uniform along the axis of rotation. The configuration of the high-frequency field is such that the electrical component of the field is directed along the constant magnetic field, while the latter does not influence the effectiveness of the action of the high-frequency field on the plasma.It is assumed that the collision frequency v of the charged particles in the plasma is non-zero. Taking into account entrainment of the plasma by the high-frequency field, one can use -instead of the second wave of the alternating field -the constant magnetic field of a multipole configuration, which behaves as a high-frequency field relative to the rotating plasma. The distribution of the plasma rotation velocity v the charged particle concentrations N and the strength of the alternating fields £L, and ff r along the plasma column radius are determined by a system of Maxwellian equations and equations of motion for the ions and electrons. A system of equations with boundary conditions is solved by computer, and the radial dependences of the angular velocity of rotation, the plasma concentration and the high-frequency fields for different values of the multipole magnetic field and the plasma concentration are ascertained. If the ratio of the field strengths at the plasma boundary is of the order of unity, then the plasma column has a tubular structure.In the case of a rotating plasma, the radial distribution of the high-frequency field is of a peculiar type.

The paper presents theoretical calculations and the results of experimental studies of the behaviour of a plasma contained in a strong constant magnetic field when a rotating high-frequency field of dipole configuration with frequency Ω is superimposed upon it. It is shown that for υei > Ω (where υei is the frequency of collisions between electrons and ions) the high-frequency field excites an azimuthal electric current jφ on the plasma surface. The interaction between the current jφ and the constant magnetic field Hz generates a dynamic force, which forms the plasma into a column.The plasma is compressed into a column when the vector of the angular velocity of rotation of the high-frequency field and that of the constant magnetic field H⃗0 coincide in direction. When the plasma is compressed into a column, there is no contact with the walls of the vacuum chamber and the degree of ionization is close to total. Probe and microwave measurements have shown that the time of compression of a plasma into a column for Hz = 8 × 103 – 1 × 104 Oe is ∼ 300 μs and the rate 6 × 103 cm/s. The diameter of the column was of the order of 2–3 cm. The charged-particle concentration measured with the help of superhigh-frequency waves (λ = 2 mm, 8 mm and 32 mm) was greater than 2 × 1014 cm−3 and decreased by more than two orders at a distance of 1−1.5 cm from the column centre.When the vectors and H⃗0 are opposite in direction, the force is directed away from the axis, and in this case, the plasma in the form of a hollow cylinder is situated at the vacuum-chamber walls.The maximum strength of the rotating high-frequency field at 1.25 MHz was 100 Oe. The results obtained show good agreement with the theoretical calculations.