The effect of emissive biased limiter on the magnetohydrodynamic modes in the IR-T1 tokamak

Abstract

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.

Study of MHD Activities in IR-T1 Tokamak Plasma Using Hilbert-Huang Transform

“…The signal from each coil can be recorded by oscilloscope (four channels) with 20 MS/s sampling rate and data acquisition with 2 MS/s sampling rate. Evidence of MHD instabilities at low value edge safety factor q(a) has been previously reported in the IR-T1 tokamak [19][20][21][22]. Figure 1 shows the temporal evolution of the plasma current and the corresponding loop voltage, Mirnov signals, and edge safety factor for shot 967425-12.…”

The effect of biased limiter on the magnetic island width in tokamak plasma

“…The SVD is a powerful mathematical tool well suited to study spatially extended systems. It detects signal features relevant to the dynamics of the system as a whole (Ghasemloo et al 2013). SVD is applied to a time space matrix of multichannel mirnov coils data.…”