Study of internal transport barrier triggering mechanism in tokamak plasmas

Dong, J. Q.; Mou, Z. Z.; Long, Y. X.; Mahajan, S. M.

doi:10.1063/1.1808750

Cited by 30 publications

(33 citation statements)

References 11 publications

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“…19,17 The generation of sheared flows by the MHD modes has been conjectured to be able to suppress the transport driven by the electrostatic microturbulence. 20,21 However, the mechanism of the MHDgenerated sheared flows has not been tested in a fully self-consistent nonlinear simulation treating both MHD modes and microturbulence. In short, the experimental evidence of the correlation between the formation of internal transport barriers and the q min crossing an integer is not well understood.…”

Section: Introductionmentioning

confidence: 99%

Properties of microturbulence in toroidal plasmas with reversed magnetic shear

Deng

Zhang

2009

Physics of Plasmas

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Electrostatic drift wave turbulence in tokamak plasmas with reversed magnetic shear is studied using global gyrokinetic particle simulations. The linear eigenmode of the ion temperature gradient (ITG) instability exhibits a mode gap around the minimum safety factor (qmin) region, particularly when qmin is an integer, due to the rarefaction of rational surfaces. The collisionless trapped electron mode (CTEM) instability is suppressed in the negative-shear region due to the reversal of the toroidal precessional drift of trapped electrons. However, after nonlinear saturation, the ITG gap is filled up by the turbulence spreading and the CTEM fluctuation propagates into the stable negative-shear region. The steady state turbulence occupies the whole volume without any identifiable gap or coherent structures of the heat conductivity, perturbed temperature, or zonal flows in the qmin location or the reversed shear region. Our finding indicates that the electrostatic drift wave turbulence itself does not support either linear or nonlinear mechanism for the formation of internal transport barriers in the reversed magnetic shear when qmin crossing an integer.

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Section: Introductionmentioning

confidence: 99%

Properties of microturbulence in toroidal plasmas with reversed magnetic shear

Deng

Zhang

2009

Physics of Plasmas

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“…The magnetic field is approximated as B B Tẑ r ẑ with x; y the magnetic flux given in Refs. [21,22]. And with q s m=n the safety factor on the double resonance surfaces, and R 0 the major radius of the device, we can choose an a on the order of the minor radius to satisfy…”

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confidence: 99%

“…Multiple current layers are often formed in various solar and astrophysical plasmas [5][6][7][8][9][10][11], as well as in magnetic confinement configurations with a reversed magnetic shear, or nonmonotonic profile of the safety factor q, desirable for high performances and steady state operations of advanced tokamaks [12 -14]. It is well known that such systems are subject to double, triple, or even multiple tearing modes (DTM [9,[15][16][17][18][19][20][21][22][23][24][25], TTM [5,6,26,27], or MTM [11]). One of the necessary conditions for the DTM to develop is that the distance between the two resonant surfaces has to be close enough to get the modes coupled.…”

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confidence: 99%

Fast Resistive Reconnection Regime in the Nonlinear Evolution of Double Tearing Modes

et al. 2007

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Phases of nonlinear double tearing modes are studied numerically. The first two phases lead to the formation and growth of magnetic islands and are followed by a fast reconnection phase to complete the process, driven by a process of neighboring magnetic separatrices merging and magnetic islands coupling. The fast growth can be understood as a result of the island interaction equivalent to a steadily inward flux boundary driven. Resistivity dependences for various phases are studied and shown by scaling analysis for the first time. It is found that after an early Sweet-Parker phase with a eta(1/2)-scale, a slow nonlinear phase in a Rutherford regime with a eta(1)-scale is followed by the fast reconnection phase with a eta(1/5)-scale.

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“…Other physical mechanisms may also play a role in shear flow generation near low-order rational-q surfaces in some discharge scenarios. Double tearing modes [27], for example, have been associated with ITB formation. However the discharges presented here did not show MHD activity so this process is not active in these particular plasmas.…”

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confidence: 99%

Localized Turbulence Suppression and Increased Flow Shear near theq=2Surface during Internal-Transport-Barrier Formation

et al. 2009

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Broadband turbulent fluctuations in the plasma density are transiently suppressed when low-order rational q surfaces first appear in negative central magnetic shear plasmas on the DIII-D tokamak, which can lead to the formation of internal transport barriers. Increased localized flow shear is simultaneously observed. It transiently exceeds the measured turbulence decorrelation rate, providing a mechanism to trigger the formation of the transport barrier. This increased flow shear and turbulence suppression propagates radially outward, following the q=2 surface.

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Study of internal transport barrier triggering mechanism in tokamak plasmas

Cited by 30 publications

References 11 publications

Properties of microturbulence in toroidal plasmas with reversed magnetic shear

Properties of microturbulence in toroidal plasmas with reversed magnetic shear

Fast Resistive Reconnection Regime in the Nonlinear Evolution of Double Tearing Modes

Localized Turbulence Suppression and Increased Flow Shear near theq=2Surface during Internal-Transport-Barrier Formation

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