Abstract
On the spherical tokamak Globus-M2 in discharges with toroidal magnetic field B= 0.7 T by means of magnetic probes and a number of other diagnostics during neutral beam injection at the current ramp up stage, magnetic field oscillations in the range of 100-300 kHz having their frequency increasing in time, had been observed. Eigenmodes with wavenumbers $n = 1-3$ (toroidal number) and $m = 2-4$ (poloidal number) were being registered. These oscillations were identified as Alfven cascades. By means of multi-channel fluctuation reflectometer, observed eigenmodes were found to be localized near magnetic shear reversal radius. Application of MHD-spectroscopy technique allowed us to determine safety factor $q_{min}$ temporal evolution and experimental values are in well agreement with modelling results, provided by ASTRA transport code.
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