Fluctuations of the poloidal component of the plasma magnetic field in the frequency range of 0.5–50 kHz are studied in the Uragan-3M (U-3M) torsatron. Hydrogen plasma is produced and heated by RF fields at frequencies close to that of the ion cyclotron. The studies are carried out using a set of 15 magnetic sensors installed in one of the torus cross sections. RF heating provided the plasma with rare collision frequencies and the presence of the bootstrap current. The study is carried out when the maximum amplitude of magnetic fluctuations is observed and their connection with the plasma energy content is noticeable. Two types of vibrations are observed. In the first type, the current structure rotates with a certain frequency mainly in the direction of the rotation of electrons in the magnetic field, and the amplitude varies slowly with time (the rotating structure). For the second type, the spatial structure does not rotate, but its amplitude changes with a certain frequency (the standing structure). The frequencies of fluctuations and rotations are close for structures with a given poloidal wave number. The standing vibration structures with different poloidal wave numbers in this frequency range are correlated. The maximum amplitude of the rotating structures is observed with m = 2, and for the standing structures with m = 3 and reaches the values of $$\tilde {B}$$ ≤ 0.3 G in the confinement region. The vibration frequency does not depend on poloidal wave number m for the studied cases; m = 0, 1, 2, 3.
The plasma energy content in the Uragan-3M torsatron was determined by means of diamagnetic measurements under the conditions of its radiofrequency (RF) generation and heating (at near ion-cyclotron frequencies) in the presence of bootstrap current. The balance of power under the fast heating of plasma was considered and used as a basis to estimate the radiofrequency power absorbed by the plasma in the confinement volume. The behavior of energy losses in the discharge period was calculated, and the effect of magnetic field fluctuations on the energy losses within a frequency range of 0.5–70 kHz was discussed.
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