Global simulations of ion turbulence with magnetic shear reversal

Garbet, X.; Bourdelle, C.; Hoang, G. T.; Maget, P.; Benkadda, S.; Beyer, Peter; Figarella, C.; Voitsekovitch, I.; Agullo, O.; Bian, N. H.

doi:10.1063/1.1367320

Cited by 145 publications

(125 citation statements)

References 47 publications

Supporting

Mentioning

118

Contrasting

Order By: Relevance

“…23) for the neoclassical parallel viscosity which is strictly valid for time scale larger than an ion collisional time. 24 For simplicity, we neglect here the contribution from the radial derivative of toroidal rotation. Thus, all aspects of toroidal rotation and parallel flow are neglected.…”

Section: Simulation Modelmentioning

confidence: 99%

Flux-driven simulations of turbulence collapse

et al. 2015

View full text Add to dashboard Cite

Using three-dimensional nonlinear simulations of tokamak turbulence, we show that an edge transport barrier (ETB) forms naturally once input power exceeds a threshold value. Profiles, turbulence-driven flows, and neoclassical coefficients are evolved self-consistently. A slow power ramp-up simulation shows that ETB transition is triggered by the turbulence-driven flows via an intermediate phase which involves coherent oscillation of turbulence intensity and E Â B flow shear. A novel observation of the evolution is that the turbulence collapses and the ETB transition begins when R T > 1 at t ¼ t R (R T : normalized Reynolds power), while the conventional transition criterion (x EÂB > c lin where x EÂB denotes mean flow shear) is satisfied only after t ¼ t C ( >t R ), when the mean flow shear grows due to positive feedback. V C 2015 AIP Publishing LLC.

show abstract

Section: Simulation Modelmentioning

confidence: 99%

Flux-driven simulations of turbulence collapse

et al. 2015

View full text Add to dashboard Cite

show abstract

“…In addition, it is assumed that the spatial variations of density and temperature are small. 24 In order to include ion temperature gradient instabilities, ion temperature fluctuation is included by using the Landau fluid closure, [25][26][27] while electron temperature fluctuation is omitted. A reduced two-fluid model in twodimensional slab geometry is obtained by assuming that the plasma is uniform along the strong guide field directed along the z-axis.…”

Section: A Simulation Modelmentioning

confidence: 99%

Turbulence driven magnetic reconnection causing long-wavelength magnetic islands

Ishizawa

Nakajima

2010

Physics of Plasmas

View full text Add to dashboard Cite

Magnetic reconnection caused by turbulence in a current sheet is studied by means of numerical simulations of fluid equations. It is found that turbulence produces long-wavelength magnetic islands even if the current sheet is so thick that spontaneous magnetic reconnection does not occur. Thus, turbulence modifies the threshold of magnetic island formation predicted by the conventional theory of spontaneous magnetic reconnection in a current sheet. In spite of the fact that the turbulence is driven by a short-wavelength instability due to a pressure gradient, the length of the magnetic island is the same order as the system size. The width of the island is several times the ion Larmor radius, and stronger turbulence causes wider magnetic islands. This suggests that the turbulence can trigger neoclassical tearing modes, which are the main nonlinear instability that limits the plasma pressure in magnetically confined plasmas. The long-wavelength magnetic island is formed by merging of small-scale magnetic islands.

show abstract

“…6,7 The second relies on the existence of intrinsically good magnetic surfaces having highly irrational q values which are in close proximity to low-order rational surfaces. This is essentially the basis for models invoking rarefaction of rational surfaces, 9 noble cantor sets, 10 and paleoclassical transport. 11 Experimentally distinguishing between the two cases would at first glance seem to be easy; since with evolving q profiles the gap in rational surfaces is encountered before the rational a͒ This paper is based on an invited paper presented at the annual APS DPP Meeting in Denver, Colorado, October 2005.…”

Section: Introductionmentioning

confidence: 99%

Core barrier formation near integer q surfaces in DIII-D

Austin¹,

Burrell

Waltz

et al. 2006

Physics of Plasmas

View full text Add to dashboard Cite

Recent DIII-D experiments have significantly improved the understanding of internal transport barriers (ITBs) that are triggered close to the time when an integer value of the minimum in q is crossed. While this phenomenon has been observed on many tokamaks, the extensive transport and fluctuation diagnostics on DIII-D have permitted a detailed study of the generation mechanisms of q-triggered ITBs as pertaining to turbulence suppression dynamics, shear flows, and energetic particle modes. In these discharges, the evolution of the q profile is measured using motional Stark effect polarimetry and the integer qmin crossings are further pinpointed in time by the observation of Alfvén cascades. High time resolution measurements of the ion and electron temperatures and the toroidal rotation show that the start of improved confinement is simultaneous in all three channels, and that this event precedes the traversal of integer qmin by 5–20ms. There is no significant low-frequency magnetohydrodynamic activity prior to or just after the crossing of the integer qmin and hence magnetic reconnection is determined not to be the precipitant of the confinement change. Instead, results from the GYRO code point to the effects of zonal flows near low order rational q values as playing a role in ITB triggering. A reduction in local turbulent fluctuations is observed at the start of the temperature rise and, concurrently, an increase in turbulence poloidal flow velocity and flow shear is measured with the beam emission spectroscopy diagnostic. For the case of a transition to an enduring internal barrier the fluctuation level remains at a reduced amplitude. The timing and nature of the temperature, rotation, and fluctuation changes leading to internal barriers suggests transport improvement due to increased shear flow arising from the zonal flow structures.

show abstract

Global simulations of ion turbulence with magnetic shear reversal

Cited by 145 publications

References 47 publications

Flux-driven simulations of turbulence collapse

Flux-driven simulations of turbulence collapse

Turbulence driven magnetic reconnection causing long-wavelength magnetic islands

Core barrier formation near integer q surfaces in DIII-D

Contact Info

Product

Resources

About