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

Ghasemloo, Maryam; Ghoranneviss, M.; Salem, M. K.

doi:10.1017/s0022377813001190

Cited by 2 publications

(3 citation statements)

References 44 publications

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“…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.…”

Section: Ir-t1 Tokamak Mirnov Coil Experimental Resultssupporting

confidence: 53%

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

2019

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In the IR-T1 tokamak plasma, study of the MHD activities is presented by using the combination of singular value decomposition (SVD) and Hilbert-Huang transform (HHT). In this work, we have proposed the SVD+HHT method to study the MHD activity for mode number identification and time-frequency behavior. Also, we have used spatio-temporal structures of the Mirnov coil fluctuations in terms of correlation function to better identification of mode number and frequencies of dominant MHD modes. High correlation values of spatio-temporal wave-like structures in lifetime below 0.1 ms in the different poloidal separation were observed. It was shown that the main frequency rotation of the MHD activities is above 10 kHz. Spatio-temporal wave-like structures, with maximum value in poloidal separation 120 or 180 degrees, show that the wavelength of the MHD mode is related to m = 2 and m = 3. Also, there are small-scale structures, mostly contributed by high-frequency short wavelength fluctuating component in the bottom of the poloidal separation 90 degrees related to m = 4 or m = 5 mode numbers. These results have been compared with the SVD + HHT analysis results. In addition, amplitude modulation of Mirnov oscillations in IR-T1 tokamak plasma generates intra-wave frequency modulation. These amplitude variations of MHD oscillations cause a frequency fluctuation. Our results have indicated that in the Hilbert spectrum (HT) analysis, the intra-wave frequency modulation is small compared to the short-time Fourier transform (STFT) and wavelet transform (WT) spectrum.

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Section: Ir-t1 Tokamak Mirnov Coil Experimental Resultssupporting

confidence: 53%

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

2019

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“…On NSTX, the plasma rotation is also found to stabilize the m/n=3/2 mode [19]. In some medium or small size tokamaks, the plasma parameters and flows are changed by the biased electrode [20][21][22][23][24][25][26][27]. Suppression of MHD activity with electrode [25] or limiter biasing [26,27] has been observed in experiments.…”

Section: Introductionmentioning

confidence: 86%

“…In some medium or small size tokamaks, the plasma parameters and flows are changed by the biased electrode [20][21][22][23][24][25][26][27]. Suppression of MHD activity with electrode [25] or limiter biasing [26,27] has been observed in experiments. There is clear yet again an advantage for improved tearing stability by having strong applied torque and driving large rotation.…”

Section: Introductionmentioning

confidence: 99%

The rapid response of 2/1 tearing mode to electrode biasing in J-TEXT experiments

Wang¹,

Chen²,

et al. 2019

Plasma Phys. Control. Fusion

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The effects of electrode biasing (EB) on the m/n = 2/1 tearing modes(TM) have been experimentally studied in J-TEXT tokamak, where m and n are the poloidal and toroidal mode numbers. According to the response time, the response of 2/1 tearing mode to EB can be divided into two processes, the rapid response and the slow response. In the rapid response, what needs to be noted is that the variation of EB current is proportional to the variation of tearing mode frequency, regardless of the EB current rise time, position of electrode, and bias voltage. On the base of that EB can supply a torque to change the tearing mode frequency quickly, the EB has been applied to unlock the locked mode. The experimental results show that the mode locking can be avoided by the negative bias voltage. While, it's unfortunately that the EB can't unlock the locked mode in recent experiments, which is different from our conjecture. In summary, the experimental results suggest that applied electrode biasing is a possible method for the avoidance of mode locking and disruption.

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

Cited by 2 publications

References 44 publications

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

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

The rapid response of 2/1 tearing mode to electrode biasing in J-TEXT experiments

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