Plasma stabilization by a high-frequency rotational field

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.