In this work the effects of Cold Biased Limiter (CBL) and Emissive Biased Limiter (EBL) have been individually investigated, in both positive and negative polarities, on the width and frequency of magnetic islands. The effects were examined using singular value decomposition and wavelet techniques on mirnov coil signals. The results show that the application of EBL with both positive and negative polarities has been more effective on plasma stability compared with CBL. Comparing different polarities of CBL and EBL revealed that the positive polarity was more effective on the width of magnetic islands than negative polarity. The greatest impact occurs during EBL with positive polarity, in which reduction is observed in both width of magnetic islands and emission of Hα radiation. Besides, intensity and frequency of magnetic islands are reduced from 50 to 25 kHz in around 1 ms after bias application. Meanwhile, the minimal effect on width and frequency of magnetic field occurs in CBL with negative polarity.

A moveable emissive biased limiter (EBL) for the investigation of spatial and temporal structure of MHD modes in IR-T1 tokamak, based on mirnov oscillations, was designed and constructed. The biasing has been considered to improve the global confinement by setting up an electric field at the plasma edge. Radial electric field (Er) modifies edge plasma turbulence, plasma rotation, and transport. Mirnov oscillations using singular value decomposition (SVD) and wavelet techniques were analyzed. SVD algorithm has been employed to analyze the frequency and wavenumber harmonics of the MHD fluctuations. The time-resolved frequency component analysis has been performed using wavelets. The EBL was applied to plasma at 10 ms with negative polarity. The results show that after applying EBL, the m = 2 mode is grown, m = 3 mode is suppressed, and Hα radiation is decreased. Furthermore, results of the wavelet analysis of mirnov coil in the time range of 8–12 ms indicate that 1.5 ms after applying EBL, the MHD frequency is reduced from 45 kHz to 25 kHz.

In this paper, The first results of the movable emissive limiter biasing experiments performed on the IR-T1 Tokamak are presented. For this purpose, a moveable emissive limiter system was designed, constructed, and installed on the IR-T1 Tokamak. The emissive biased limiter is positioned at r/a=1.05, and the biased voltage which is varied from -350 to 350 V applied between the head of emissive limiter and vacuum chamber. Then, the plasma current, safety factor, poloidal beta and plasma resistance in the absence and presence of the emissive biased limiter in negative polarity were measured and results were compared with the cold limiter biasing in negative polarity. Much more plasma parameters such as the magneto hydrodynamics instability and plasma energy confinement time are determined by using these parameters. Diamagnetic loops and loop voltage can be utilized in measurements of the plasma poloidal beta and plasma resistance. Result are compared and discussed.

No abstract

No abstract