Nonlocal effects in gyrokinetic turbulence simulations using GENE

Abstract

Modeling of anomalous transport, typically based on gyrokinetic theory, is an essential tool for better understanding and possibly improving the confinement of magnetic fusion plasmas. A well-benchmarked and established implementation of the gyrokinetic Vlasov-Maxwell system of equations can, for instance, be found in the software package Gene. This Eulerian code has recently been enhanced to optionally consider full radial temperature, density, and geometry variations allowing for investigations of nonlocal effects instead of using the radially local flux-tube approximation. First investigations on the importance of finite-size effects are presented and compared with results from the gyrokinetic Lagrangian PIC code ORB5 [S. Jolliet et al. 2007 Comput. Phys. Commun. 177 409, B.F. McMillan et al. 2008 Phys. Plasmas 15 052308]. Special attention is drawn to a specific nonlocal effect, namely heat flux avalanches.

A statistical analysis of avalanching heat transport in stationary enhanced core confinement regimes

“…This propagation speed falls within a range of q à v g =c s q à , where is the inverse aspect ratio, although this scaling is uncertain in this work, due to the lack of q à scan. Recent full-f gyrokinetic simulations report that v g follows the scaling [15][16][17] which seem to agree with our observation. The retardation of an outward pulse is due to the presence of strong x EÂB at ITB foot position, as indicated in Fig.…”

“…Experiments [7][8][9][10][11][12] and numerical simulations [13][14][15][16][17] have often shown the existence of non-local heat avalanches in magnetically confined plasmas, in addition to local diffusive transport. In particular, a recent gyrokinetic simulation study highlights one self-organization process, which can determine transport: the prevalence of self-organized, avalanche-dominated transport on mesoscales (with a Lorentzian kernel), and the persistence of static E Â B staircases, the spacing of which defines the outer scale of the avalanche distribution.…”

“…23,[26][27][28][29] In numerical simulations, many papers have been devoted to the study of avalanching heat transport in magnetically confined plasmas with varying degrees of numerical sophistication. 13,18,[30][31][32] Many features of heat avalanches were studied, for instance, the scaling of the propagation speed of a heat pulse, [15][16][17] the long range spatio-temporal correlations, 18 and the appearance of a 1/f power spectrum. 31 However, the physics of avalanching heat transport has not been fully explored so far, especially in the context of a selfconsistently generated enhanced confinement regime.…”

Gyrokinetic prediction of microtearing turbulence in standard tokamaks

“…The local approximation is expected to hold when the tokamak minor radius a becomes much larger than the gyroradius ρ i . While finite machine size effects usually stabilize modes like the ITG instability due to profile shearing, [28][29][30] it is a priori not clear how microtearing modes are affected. In the present work, we relax these constraints in the context of linear and nonlinear gyrokinetic simulations, employing realistic ASDEX Upgrade (AUG) parameters.…”

A study of self organized criticality in ion temperature gradient mode driven gyrokinetic turbulence

“…So far, only the appearance of avalanches has been reported in gyrokinetic simulations by many authors in various kinds of simulations, i.e. avalanches are detected in local 23 and global 24 gyrokinetic simulations. There have also been studies using gyrokinetic simulations concerning the effect of rotation on avalanches 25 , and mainly on how avalanches influence transport [26][27][28] .…”