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The synchrotron radiation diagnostics allows a direct observation of the runaway electron beams and an analysis of their parameters. Strong oscillations of the instantaneous curvature radii of electron orbits were a characteristic feature of recent EAST and KSTAR tokamak runaway electron experiments. Incorrect analysis of synchrotron radiation spectra of runaway electrons was carried out by EAST team. In presented paper the detail theoretical analysis of the synchrotron radiation spectra of the runaway electrons which gyrate around their guiding centers in the curved magnetic field is presented for cases when the curvature radius of electron orbit oscillates strongly. Key parameter of the analysis is the ratio of the cyclotron rotation velocity to the velocity of the vertical centrifugal drift. This analysis is applied for correct calculations of synchrotron radiation spectra for EAST and KSTAR runaway electron parameters.

Recently the possibility of resonant excitation of pressure perturbation by external helical magnetic perturbations near the rotating plasma edge was shown taking into consideration the finite plasma conductivity. In present paper the influence of the small safety factor variation on the pressure perturbation and on the plasma current response is studied. This phenomenon may explain the existence of the small window of safety factor values where ELMs were completely eliminated. The possibility to control the plasma current response to penetration of external helical resonant magnetic perturbations into the edge plasmas is shown. The investigation is carried out in the frame of one-fluid MHD.