Xiao, Chijin2024-06-0320242024-042024-06-03April 2024https://hdl.handle.net/10388/15741Experimental studies of the fluctuating flux and turbulences have been active topics in the tokamak research in order to improve plasma confinement purposes. The electrode biasing and wall conditioning have crucial effect on the plasma transport and fluctuating flux suppression at the edge region of the plasma. Electrode biasing involves a modification on the edge radial electric field which in turn generates shear drift that suppresses the plasma fluctuations. The electrode biasing experiment is carried out in the Saskatchewan Torus-Modified (STOR-M) tokamak using an arc-shaped electrode. Different biasing voltage waveforms have been applied with and without lithium (Li) coated walls. In DC electrode biasing experiment, when the electrode was biased at -390V a change in flux direction from outward to inward in addition to increase plasma density have been observed. Also, a suppression in the fluctuating flux with changing in its direction to inward due to the phase decorrelation between the plasma density and poloidal electric field fluctuations is noticed. Conducting DC-biasing experiment with Li coating gives strong evidence of edge transport formation at radial location where the plasma temperature and density increase significantly, and flux direction is reversed to inward. In bi-polar multi-pulse biasing experiment, a suppression in the fluctuating flux is noticed also during the negative biasing pulses. Also, the suppression in the flux turbulences has been observed in the low frequency and quasi-coherent modes frequency ranges. DC electrode biasing has been applied with resonant magnetic perturbation (RMP) since RMP has favorable effects on magnetohydrodynamic (MHD) stabilities. Application of both electrode biasing and RMP supresses the magnetic fluctuations in addition to the fluctuating flux which increase the plasma confinement. Moreover, the electrode biasing experiment has been conducted during the neutral beam injection in the TJ-II stellarator. The suppression in the fluctuating flux during the negative biasing pulses (-370V) is noticed. Also, the direction of energy propagation or floating potential fluctuation propagation in TJ-II has been studied using the non-linear correlation analysis. In TJ-II, during application both NBI and negative electrode biasing pulses, the energy propagation direction is revered from outward to inward as an indication of improved plasma energy confinement.application/pdfenTokamakStellaratorelectrode biasingturbulencesfluctuationplasmaThesis2024-06-03