Effect of electrostatic turbulence on magnetic islands

Waelbroeck, F. L.; Militello, F.; Fitzpatrick, Richard; Horton, W.

doi:10.1088/0741-3335/51/1/015015

Cited by 45 publications

(56 citation statements)

References 33 publications

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“…The structure of the D pol curve for this value of the island width may be related to the oscillation due to drift waves observed in Ref. 17, although here the force curve is much smoother due to the higher values of viscosity and diffusivity in our simulations. When the width of the simulation box is smaller and closer to the island width, however,…”

Section: A Incompressible Plasmasupporting

confidence: 47%

“…Except for the evolution of the ion temperature, this case is analogous to the simulations in Ref. 17. The second is referred to as the "cold ion" case.…”

Section: Forced Island Propagationmentioning

confidence: 92%

“…The current density thus vanishes (J ¼ 0), since the applied E Â B flow totally cancels out the equilibrium electron diamagnetic flow, resulting in F y ¼ 0 and D pol ¼ 0. 17 The force F y is proportional to u free À u, with a proportionality constant that increases with the island width. The curves of D pol , by contrast, resemble parabolas, consistent with Eq.…”

Section: A Incompressible Plasmamentioning

confidence: 99%

“…15 A second possibility is that turbulence can induce growth indirectly by braking the island rotation, thereby producing a destabilizing polarization current. 16,17 More recently, two of us have demonstrated a third mechanism whereby ion temperaturegradient turbulence can robustly give rise to magnetic islands of size several times the ion Larmor radius, which may be sufficient to initiate NTM growth. 18 These islands are created by a process of merging, through inverse cascade, of the much smaller-scale magnetic islands that are formed as a by-product of ion temperature gradient driven (ITG) turbulence in finitebeta plasma.…”

Section: Introduction a Motivationmentioning

confidence: 99%

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Magnetic island evolution in hot ion plasmas

et al. 2012

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Effects of finite ion temperature on magnetic island evolution are studied by means of numerical simulations of a reduced set of two-fluid equations which include ion as well as electron diamagnetism in slab geometry. The polarization current is found to be almost an order of magnitude larger in hot than in cold ion plasmas, due to the strong shear of ion velocity around the separatrix of the magnetic islands. As a function of the island width, the propagation speed decreases from the electron drift velocity (for islands thinner than the Larmor radius) to values close to the guiding-center velocity (for islands of order 10 times the Larmor radius). In the latter regime, the polarization current is destabilizing (i.e., it drives magnetic island growth). This is in contrast to cold ion plasmas, where the polarization current is generally found to have a healing effect on freely propagating magnetic island.

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Section: A Incompressible Plasmasupporting

confidence: 47%

“…Except for the evolution of the ion temperature, this case is analogous to the simulations in Ref. 17. The second is referred to as the "cold ion" case.…”

Section: Forced Island Propagationmentioning

confidence: 92%

Section: A Incompressible Plasmamentioning

confidence: 99%

Section: Introduction a Motivationmentioning

confidence: 99%

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Magnetic island evolution in hot ion plasmas

et al. 2012

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“…Turbulence has been shown to modify the stability and dynamics of the tearing mode [9,10,11,12]. Furthermore, the influence of mesoscale magnetic island structures on small scale turbulence (and vice versa) is expected to affect heat and particle transport properties [13,14,15].…”

mentioning

confidence: 99%

The nonlinear coupling between gyroradius scale turbulence and mesoscale magnetic islands in fusion plasmas

et al. 2010

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The interaction between small scale turbulence (of the order of the ion Larmor radius) and meso-scale magnetic islands is investigated within the gyrokinetic framework. Turbulence, driven by background temperature and density gradients, over nonlinear mode coupling, pumps energy into long wavelength modes, and can result in an electrostatic vortex mode that coincides with the magnetic island. The strength of the vortex is strongly enhanced by the modified plasma flow response connected with the change in topology, and the transport it generates can compete with the parallel motion along the perturbed magnetic field. Despite the stabilizing effect of sheared plasma flows in and around the island, the net effect of the island is a degradation of the confinement. When density and temperature gradients inside the island are below the threshold for turbulence generation, turbulent fluctuations still persist through turbulence convection and spreading. The latter mechanisms then generate a finite transport flux and, consequently, a finite pressure gradient in the island. A finite radial temperature gradient inside the island is also shown to persist due to the trapped particles, which do not move along the field around the island. In the low collisionality regime, the finite gradient in the trapped population leads to the generation of a bootstrap current, which reduces the neo-classical drive.

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A compressible Hamiltonian electromagnetic gyrofluid model

Waelbroeck

Tassi

2012

Communications in Nonlinear Science and Numerical Simulation

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A Lie-Poisson bracket is presented for a four-field gyrofluid model with compressible ions and magnetic field curvature, thereby showing the model to be Hamiltonian. In particular, in addition to commonly adopted magnetic curvature terms present in the continuity equations, analogous terms must be retained also in the momentum equations, in order to have a Lie-Poisson structure.The corresponding Casimir invariants are presented, and shown to be associated to four Lagrangian invariants, that get advected by appropriate "velocity" fields during the dynamics. This differs from a cold ion limit, in which the Lie-Poisson bracket transforms into the sum of direct and semidirect products, leading to only three Lagrangian invariants.

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Effect of electrostatic turbulence on magnetic islands

Cited by 45 publications

References 33 publications

Magnetic island evolution in hot ion plasmas

Magnetic island evolution in hot ion plasmas

The nonlinear coupling between gyroradius scale turbulence and mesoscale magnetic islands in fusion plasmas

A compressible Hamiltonian electromagnetic gyrofluid model

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