Kinetic theory of tearing instability

Hazeltine, R. D.; Dobrott, D.; Wang, T. S.

doi:10.1063/1.861097

Cited by 183 publications

(166 citation statements)

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“…Two destabilizing effects for the electron temperature gradient drive have been reported. One of them is the time-dependent thermal force [8,9,[13][14][15][16], the second is the influence of the collisionality at the trapped-passing boundary [10,17,18]. Moreover, a destabilizing contribution of the electrostatic potential to the parallel electric field inside the current layer has been found in semi-analytic work.…”

Section: Introductionmentioning

confidence: 84%

“…First results in this area have aleady been obtained in the 1970's by several authors. [8][9][10][11] Moreover, it has recently been proposed that in finite β ITG/TEM turbulence, linearly stable microtearing modes can be excited via a nonlinear coupling to zonal modes. [5] Interestingly, this can explain both the occurrence of stochastic fields [6] and the quadratic scaling of the magnetic transport which contradicts standard quasilinear transport models.…”

Section: Introductionmentioning

confidence: 99%

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Gyrokinetic prediction of microtearing turbulence in standard tokamaks

et al. 2012

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First global gyrokinetic simulations of microtearing instabilities in ASDEX Upgrade geometry provide increasing evidence for the existence of these modes in standard tokamaks. It is found that even in only moderately large devices, nonlocal effects like profile shearing are negligible, supporting the use of an efficient flux-tube approach. Nonlinear gyrokinetic simulations show that the resulting level of magnetic electron heat flux can be experimentally relevant.

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Section: Introductionmentioning

confidence: 84%

Section: Introductionmentioning

confidence: 99%

Gyrokinetic prediction of microtearing turbulence in standard tokamaks

et al. 2012

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“…We demonstrate, through simulations using the gyrokinetic code Gene [9,10], that the microtearing mode (MTM) [11][12][13][14] is the dominant instability in the pedestal. Interestingly, the simulations do not find the kinetic ballooning mode (KBM), a basic component of the EPED model, except locally in a narrow region near the separatrix.…”

Section: Pacs Numbersmentioning

confidence: 99%

Microtearing turbulence limiting the JET-ILW pedestal

et al. 2016

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Gyrokinetic simulations identify microtearing modes (MTM) to be the dominant microinstabilities in the JET-ILW (ITER like wall) pedestal. Nonlinear simulations show that MTM-driven turbulence produces the bulk of the transport in the steep gradient region, demonstrating that MTM may be the principal mechanism limiting JET-ILW pedestal evolution. The combination of MTM, electron temperature gradient (ETG), and neoclassical transport reproduces experimental power balance across most of the pedestal. Kinetic ballooning modes are significant only in the local limit and only at low β, far below the experimental operating point. PACS numbers:The tokamak H-mode [1] is defined by a narrow insulating region-the pedestal-at the plasma edge, where turbulence is suppressed and sharp pressure gradients develop. The pedestal is at the center of the most pressing issues facing fusion energy. ITER, for example, must reach a sufficient temperature at the pedestal's inner boundary in order to achieve its fusion power targets [2]. This work reports the results of, perhaps, the very first, first-principles simulations of the H-mode pedestal dynamics that reproduce experimentally observed transport levels. In addition to providing unprecedented insight into the dynamics of the existing H-mode pedestals, such simulations are likely to advance our capabilities towards predictive modeling of future burning plasma devices.This study targets the JET-ILW (ITER-like wall) pedestal [4][5][6], which approaches ITER conditions in two important ways: 1) as the largest tokamak in operation, it most-closely approximates plasma parameters that are dependent on machine size (like ρ * , the ratio of the gyroradius to minor radius), 2) to approximate ITER conditions even better, JET has recently installed an ITERlike wall (ILW) (composed of a tungsten divertor and beryllium chamber). This modification decreases the global performance of discharges by 20-30%, attributable largely to changes in pedestal structure. In addition to the performance loss, certain observed key properties of the ILW pedestal are inconsistent with predictions of the leading pedestal model (EPED [7,8]).In this work, we elucidate possible mechanisms limiting profile evolution in the JET-ILW discharges. We demonstrate, through simulations using the gyrokinetic code Gene [9,10], that the microtearing mode (MTM) [11][12][13][14] is the dominant instability in the pedestal. Interestingly, the simulations do not find the kinetic ballooning mode (KBM), a basic component of the EPED model, except locally in a narrow region near the separatrix. Most importantly, we determine via nonlinear gyrokinetic simulations that a combination of MTM and electron temperature gradient (ETG) [9,[15][16][17][18] driven turbulence plus the neoclassical flux, produces transport levels closely matching experimental power balance across most of the pedestal, demonstrating the capacity of these mechanisms to limit JET-ILW pedestal evolution.The JET-ILW Pedestal-JET pulse 82585 (described in Ref. [4]) is pa...

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“…[1] A few years later, several authors suggested that one source of such fluctuations may be electromagnetic microinstabilities like microtearing modes. [2][3][4][5] The latter are gyrokinetic analogues of the well-known magnetohydrodynamic tearing modes, driven mainly by electron temperature gradients and giving rise to small-scale magnetic islands which may overlap and "stochasticize" the magnetic field. This discovery was followed by numerous theoretical and computational efforts throughout the 1980s and 1990s.…”

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confidence: 99%

Gyrokinetic Microtearing Turbulence

et al. 2011

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The nonlinear dynamics of microtearing modes in standard tokamak plasmas are investigated by means of ab initio gyrokinetic simulations. The saturation levels of the magnetic field fluctuations can be understood in the framework of a balance between (small poloidal wavenumber) linear drive and small-scale dissipation. The resulting heat transport is dominated by the electron magnetic component, and the transport levels are found to be experimentally relevant. Microtearing modes thus constitute another candidate for explaining turbulent transport in such toroidal systems.It is well established that the cross-field transport of energy and particles in magnetically confined plasmas is generally dominated by turbulent processes. Nevertheless, important aspects of turbulent transport are not well understood at present, including the role of field line stochasticity -although first major results in this area were already achieved several decades ago. In 1973, Stix argued that even minute magnetic perturbations can destroy magnetic surfaces, enhancing the radial electron heat flux.[1] A few years later, several authors suggested that one source of such fluctuations may be electromagnetic microinstabilities like microtearing modes.[2-5] The latter are gyrokinetic analogues of the well-known magnetohydrodynamic tearing modes, driven mainly by electron temperature gradients and giving rise to small-scale magnetic islands which may overlap and "stochasticize" the magnetic field. This discovery was followed by numerous theoretical and computational efforts throughout the 1980s and 1990s. However, no clear physical picture emerged concerning both nonlinear and even various linear effects; in particular, it is not entirely clear from the published analytical work whether stabilizing or destabilizing effects dominate the linear physics of microtearing modes under realistic conditions.Over the last few years, linear gyrokinetic studies have been undertaken, indicating a role of microtearing modes first in spherical (small aspect ratio) [6][7][8] and later also in standard (medium aspect ratio) [9][10][11] tokamak plasmas. Furthermore, it was shown that a semi-analytic transport prediction (using severe simplifications) by Drake and co-workers [12] is consistent with certain experimental results from the NSTX tokamak. [13] Investigations of the nonlinear dynamics of microtearing modes by means of ab initio gyrokinetic simulations would be extremely valuable in this context, but are still missing to date. This gap shall be closed in the present Letter. Below, we will investigate (i) what sets the saturation levels of the magnetic field fluctuations; (ii) in which way the magnetic fluctuation level is linked to the heat transport level; (iii) which kind of physics sets the saturation amplitudes and thus the transport levels in the quasisteady turbulent state -firmly establishing microtearing modes as additional candidates for explaining turbulent transport in (standard) tokamaks.In the following, we will employ the local (flux-tub...

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Kinetic theory of tearing instability

Cited by 183 publications

References 10 publications

Gyrokinetic prediction of microtearing turbulence in standard tokamaks

Gyrokinetic prediction of microtearing turbulence in standard tokamaks

Microtearing turbulence limiting the JET-ILW pedestal

Gyrokinetic Microtearing Turbulence

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