Gyroaverage operator for a polar mesh

International audienceIn this work, we are concerned with numerical approximation of the gyroaverage operators arising in plasma physics to take into account the effects of the finite Larmor radius corrections. The work initiated in [5] is extended here to polar geometries. A direct method is proposed in the space configuration which consists in integrating on the gyrocircles using interpolation operator (Hermite or cubic splines). Numerical comparisons with a standard method based on a Padé approximation are performed: (i) with analytical solutions, (ii) considering the 4D drift-kinetic model with one Larmor radius and (iii) on the classical linear DIII-D benchmark case [6]. In particular, we show that in the context of a drift-kinetic simulation, the proposed method has similar computational cost as the standard method and its precision is independent of the radius. PACS. PACS-key discribing text of that key – PACS-key discribing text of that ke

Quasi-neutrality equation in a polar mesh

In this work, we are concerned with the numerical resolution of the quasi-neutrality equation arising in plasma physics. A classic method is based on a Padé approximation. Two other methods are proposed in this paper: a Padé approximation of higher order and a direct method in the space configuration which consists in integrating on the gyrocircles using interpolation operator. Numerical comparisons are performed with analytical solutions and considering the 4D drift-kinetic model with one Larmor radius. This is a preliminary study; further study in GYSELA is envisioned

GENE-3D - ein globaler gyrokinetischer Turbulenzcode für Stellaratoren und gestörte Tokamaks

This thesis describes the development and application of GENE-3D, a global gyrokinetic turbulence HPC code for stellarators. The gyrokinetic equations as well as their implementation and the use of field-aligned coordinates in non-axisymmetric geometries are discussed. GENE-3D is benchmarked for validity and performance. Different geometries of Wendelstein 7-X are investigated for their influence on turbulent properties. Also the influence of the machine size on linear growth rates is studied.Diese Arbeit beschreibt die Entwicklung und Anwendung von GENE-3D, ein globaler gyrokinetischer Turbulenzcode für Stellaratoren. Die gyrokinetischen Gleichungen sowie deren Implementierung und das am Feld ausgerichtete Koordinatensystem werden für nicht-axisymmetrische Geometrien vorgestellt. GENE-3D wird auf Korrektheit getestet.Der Einfluß unterschiedlicher Wendelstein 7-X Geometrien auf den turbulenten Transport und der Einfluß der Maschinengröße auf die linearen Anwachsraten wird untersucht

A New Parallelization Scheme for the Hermite Interpolation Based Gyroaverage Operator

International audienceGyrokinetic modeling is appropriate for describing plasma turbulence in the core of Tokamaks, and the gyroaverage operator is a cornerstone of this approach. In a gyrokinetic code the gyroaveraging scheme needs to be accurate enough, but also requires a low computational cost because it is often applied on the main unknown, namely the 5D guiding-center distribution function, as well as on several 3D fields. The current gyroaverage implementation used in the GYSELA code has recently been improved [6], enhancing the precision of the operator thanks to Hermite interpolation. In the present paper, we describe a new parallelization scheme for the gyroaverage operator. It mainly avoids costly transpositions of the full 5D function using halo exchange instead. Though the computational cost remains the same, the communication one is much smaller. The overall algorithm is also improved by cleverly interleaving communications and computations, thus allowing for a reduction of communication costs and a more efficient thread parallelization. The execution time with this algorithm is up to twice as fast as the previous version. The benefit of an improved scheme providing the overlap of communications by computations is also shown, again improving execution times. The description of the algorithms is given, together with an analysis of the achieved performance