Edge Plasma Behavior during Externally Applied Electrode Biasing and Resonant Magnetic Perturbation in IR-T1 Tokamak

Full text: Edge plasma behavior during externally applied electrode biasing and resonant helical magnetic field (RHF) perturbation in IR-T1 tokamak has been investigated. The experiments have been done in different regimes as electrode biasing, magnetic perturbation application and both of them. The profiles of radial electron temperature, floating potential, poloidal and toroidal rotation velocity have been measured by using of a movable Langmuir probe and Mach probes in the edge of plasma. Magnetohydrodynamic phenomena based on Mirnov oscillations have been investigated by applying the positive electrode biasing potential and RHF. An effect of RHF on magnetohydrodynamics behaviour during positive electrode biasing has been investigated. The results shown that subsequent to the application of a positive bias, an increase in the frequency of magnetic field fluctuations was observed but after RHF application during L = 2 and n =1 (L poloidal and n toroidal turn) the m = 2 MHD mode oscillations amplified and m = 3 mode is suppressed; also by applying L = 3 RHF's the m = 2 MHD mode oscillation has been disappeared. The results analysed by SVD and wavelet methods. Simultaneous measurements of the radial electric field and poloidal magnetic field oscillations shown that magnetohydrodynamic activity is damped when the radial electric field becomes more negative in the plasma edge. The results shown that MHD frequency decreases while the radial electric field increasing negatively. The toroidal velocity changes after a short delay time of about td =1 - 1.5 ms during RHF application while poloidal velocity changes just after RHF's. The poloidal velocity increased after positive bias but it decreased after RHF application during Bias regime. Toroidal velocity hasn't considerable change during biasing but it decreased after RHF application and poloidal Mach number decreased during biasing application too. (author)