Suppression of electric and magnetic fluctuations and improvement of confinement due to current profile modification by biased electrode in Saha Institute of Nuclear Physics tokamak

Basu, Debjyoti; Pal, Rabindranath; Ghosh, Joydeep; Chattopadhyay, P. K.

doi:10.1063/1.4739074

Cited by 8 publications

(11 citation statements)

References 24 publications

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“…This corresponds to a narrower current profile compared with no biasing, in agreement with the observed current profile modification reported in Ref. 12. This is shown by the solid line in Fig.…”

Section: Analysis and Interpretation Of Resultssupporting

confidence: 90%

“…In Ref. 12, it was reported that biasing experiments improve plasma confinement by stabilizing deleterious drift modes; in Fig. 2 of Ref.…”

Section: Analysis and Interpretation Of Resultsmentioning

confidence: 98%

“…7 of Ref. 12, it is shown that the radial electric field duration is short and it begins to decay just as mode formation begins, after 5 ms into the discharge.…”

Section: Discussionmentioning

confidence: 97%

“…Specifically, without bias modes m ¼ 2 and 3 are unstable (although a coupling between them in the disruption phase makes m ¼ 2 mode imperceptible) and with bias m ¼ 3 is stable (is not excited) and m ¼ 2 is not growing (marginally stable). Based on previous results, 12,13 which show that electrode biasing produces current profile modification, it is proposed that the stabilization of tearing modes is due to changes in the current distribution. This hypothesis could be tested by computing the stability of the modes for a given current profile.…”

Section: Discussionmentioning

confidence: 98%

“…These modes are stabilized by effect of negative biasing potential and only a steady m/n ¼ 2/1 mode is observed which is too far away from the plasma edge to produce a disruption. Based on previous analyses that indicate that the edge current density profile is modified when fast electrode bias is applied, 12 we hypothesize that the most likely cause of MHD modes' stabilization is the current profile modification. Calculation of global current profiles based on the observed frequencies also indicates that the profile is narrower with bias, which supports the assertion.…”

Section: Discussionmentioning

confidence: 98%

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Disruption avoidance in the SINP-Tokamak by means of electrode-biasing at the plasma edge

et al. 2013

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Control of plasma disruption by a biased edge electrode is reported in SINP-Tokamak. The features that characterize a plasma disruption are reduced with increasing bias potential. The disruption can be completely suppressed with the concomitant stabilization of observed MHD modes that are allegedly precursors of the disruption. An m ¼ 3/n ¼ 1 tearing mode, which apparently causes disruption can be stabilized when a negative biasing potential is applied near the edge. These changes in the disruptive behavior with edge biasing are hypothesized to be due to changes in the current density profile. V C 2013 AIP Publishing LLC. [http://dx.

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Section: Analysis and Interpretation Of Resultssupporting

confidence: 90%

“…In Ref. 12, it was reported that biasing experiments improve plasma confinement by stabilizing deleterious drift modes; in Fig. 2 of Ref.…”

Section: Analysis and Interpretation Of Resultsmentioning

confidence: 98%

“…7 of Ref. 12, it is shown that the radial electric field duration is short and it begins to decay just as mode formation begins, after 5 ms into the discharge.…”

Section: Discussionmentioning

confidence: 97%

Section: Discussionmentioning

confidence: 98%

Section: Discussionmentioning

confidence: 98%

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Disruption avoidance in the SINP-Tokamak by means of electrode-biasing at the plasma edge

et al. 2013

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

et al. 2013

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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.

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Modification of tokamak edge plasma turbulence and transport by biasing and resonant helical magnetic field

Lafouti

Ghoranneviss

Meshkani

et al. 2013

Review of Scientific Instruments

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In this paper, both Resonant Helical magnetic Field (RHF) and limiter biasing have been applied to the tokamak. We have investigated their effects on the turbulence and transport of the particles at the edge of the plasma. The biased limiter voltage has been fixed at 200 V and RHF has L = 2 and L = 3. Also, the effects of the time order of the application of RHF and biasing to the tokamak have been explored. The experiment has been performed under three conditions. At first, the biasing and RHF were applied at t = 15 ms and at t = 20 ms. In the next step, RHF and biasing were applied at t = 15 ms and t = 20 ms, respectively. Finally, both of them were turned on at t = 15 ms until the end of the shot. For this purpose, the ion saturation current (I(sat)) and the floating potential (V(f)) have been measured by the Langmuir probe at r/a = 0.9. Moreover, the power spectra of I(sat) and floating potential gradient (∇V(f)), the coherency, the phase between them, and the particle diffusion coefficient have been calculated. The density fluctuations of the particles have been measured by the Rake probe and they have been analyzed with the Probability Distribution Function (PDF) technique. Also the particle diffusion coefficient has been determined by the Fick's law. The results show that, when RHF and biasing were applied at the same time to the plasma (during flatness region of plasma current), the radial particle density gradient, the radial particle flux, and the particle diffusion coefficient decrease about 50%, 60%, and 55%, respectively, compared to the other conditions. For more precision, the average values of the particle flux and the particle density gradient were calculated in the work. When the time is less than 15 ms, the average values of the particle flux and the particle density gradient are identical under all conditions, but in the other time interval they change. They reduce with the simultaneous application of biasing and RHF. The same results obtain from the histogram of the particle flux and the gradient of the particle density and the particle diffusion coefficient. Consequently, the simultaneous application of biasing and RHF is more effective for the plasma confinement.

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Suppression of electric and magnetic fluctuations and improvement of confinement due to current profile modification by biased electrode in Saha Institute of Nuclear Physics tokamak

Cited by 8 publications

References 24 publications

Disruption avoidance in the SINP-Tokamak by means of electrode-biasing at the plasma edge

Disruption avoidance in the SINP-Tokamak by means of electrode-biasing at the plasma edge

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

Modification of tokamak edge plasma turbulence and transport by biasing and resonant helical magnetic field

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