Investigation of Magnetohydrodynamic Fluctuation Modes in the STOR-M Tokamak

• Main Author: Gamudi Elgriw, Sayf
• Other Authors: Koustov, Sasha
• Format: Others
• Language: en
• Published: University of Saskatchewan 2009
• Subjects: gong; Singular Value Decomposition; wavelet; Fourier; instabilities; Magnetohydrodynamic; plasma; SXR; Mirnov; compact torus; STOR-M; tokamak; fusion
• Online Access: http://library.usask.ca/theses/available/etd-07302009-071402/

While magnetohydrodynamic (MHD) instabilities are considered one of the intriguing topics in tokamak physics, a feasibility study was conducted in the Saskatchewan Torus-Modified (STOR-M) tokamak to investigate the global MHD activities during the normal (L-mode) and improved (H-mode) confinement regimes. The experimental setup consists of 32 discrete Mirnov coils arranged into four poloidal arrays and mounted on STOR-M at even toroidal distances. The perturbed magnetic field fluctuations during STOR-M discharges were acquired and processed by the Fourier transform (FT), the wavelet analysis and the singular value decomposition (SVD) techniques. In L-mode discharges, the poloidal MHD mode numbers varied from 2 to 4 with peak frequencies in the range 20-40 kHz. The dominant toroidal modes were reported between 1 and 2 oscillating at frequencies 15-35 kHz. In another experiment, a noticeable MHD suppression was observed during the H-mode-like phase induced by the compact torus (CT) injection into STOR-M. However, a burst-like mode called the gong mode was triggered prior to the H-L transition, followed by coherent Mirnov oscillations. Mirnov oscillations with strong amplitude modulations were observed in the STOR-M tokamak. Correlations between Mirnov signals and soft x-ray (SXR) signals were found.