Xavier Lapillonne

MeteoSwiss

Classical numerical models for the global atmosphere, as used for numerical weather forecasting or climate research, have been developed for conventional central processing unit (CPU) architectures. This hinders the employment of such models on current top-performing supercomputers, which achieve their computing power with hybrid architectures, mos...

Classical numerical models for the global atmosphere, as used for numerical weather forecasting or climate research, have been developed for conventional central processing unit (CPU) architectures. This now hinders the employment of such models on current top performing supercomputers, which achieve their computing power with hybrid architectures,...

In 2015, CSCS and the Swiss national weather and climate service (a.k.a. MeteoSwiss) have deployed the first GPU accelerated HPC system for numerical weather prediction (NWP), which has been in operation since Spring of 2016. As part of the lifecycle management, an eight-times more performant system that can support an upgraded model had to be deve...

Currently major efforts are underway toward refining the horizontal resolution (or grid spacing) of climate models to about 1 km, using both global and regional climate models (GCMs and RCMs). Several groups have succeeded in conducting kilometer-scale multiweek GCM simulations and decadelong continental-scale RCM simulations. There is the well-fou...

In order to profit from emerging high-performance computing systems, weather and climate models need to be adapted to run efficiently on different hardware architectures such as accelerators. This is a major challenge for existing community models that represent very large code bases written in Fortran. We introduce the CLAW domain-specific languag...

The best hope for reducing long-standing global climate model biases is by increasing resolution to the kilometer scale. Here we present results from an ultrahigh-resolution non-hydrostatic climate model for a near-global setup running on the full Piz Daint supercomputer on 4888 GPUs (graphics processing units). The dynamical core of the model has...

The purpose of this chapter is to describe a step-by-step porting approach for weather and climate model Fortran code to run on GPUs using CUDA and OpenACC.At the end of this chapter, the reader will have a basic understanding of: How to use OpenACC to port components of a production weather and climate model achieving a gain of about a factor of 2...

The best hope for reducing long-standing global climate model biases, is through increasing the resolution to the kilometer scale. Here we present results from an ultra-high resolution non-hydrostatic climate model for a near-global setup running on the full Piz Daint supercomputer on 4888 GPUs. The dynamical core of the model has been completely r...

The representation of moist convection in climate models represents a major challenge, due to the small scales involved. Using horizontal grid spacings of O(1km), convection-resolving weather and climate models allows one to explicitly resolve deep convection. However, due to their extremely demanding computational requirements, they have so far be...

The representation of moist convection in climate models represents a major challenge, due to the small scales involved. Using horizontal grid spacings of O(1km), convection-resolving weather and climate models allow to explicitly resolve deep convection. However, due to their extremely demanding computational requirements, they have so far been li...

A COSMO consortium project devoted to spatial verification methods (INSPECT) has been created to follow MesoVICT activities and to summarize the COSMO experience of applying spatial verification methods to high and very high resolution models (deterministic and EPS). In addition to targeting the objectives of MesoVICT, INSPECT has been designed wit...

For many scientific applications, Graphics Processing Units (GPUs) can be an interesting alternative to conventional CPUs as they can deliver higher memory bandwidth and computing power. While it is conceivable to re-write the most execution time intensive parts using a low-level API for accelerator programming, it may not be feasible to do it for...

We propose a software implementation strategy for complex weather and climate models that produces performance portable, architecture agnostic codes. It relies on domain and data structure specific tools that are usable within common model development frameworks - Fortran today and possibly high-level programming environments like Python in the fut...

As a part of a larger effort to prepare the numerical weather prediction code COSMO (Consortium for Small-scale Modeling) to future high performance computing architectures, a prototype version of the model capable of running on Graphical Processor Units (GPU) is being developed. In order to avoid the high cost of transferring data between the GPU...

The understanding and prediction of transport due to plasma microturbulence is a key open problem in modern plasma physics, and a grand challenge for fusion energy research. Ab initio simulations of such small-scale, low-frequency turbulence are to be based on the gyrokinetic equations, a set of nonlinear integro-differential equations in reduced (...

Two global gyrokinetic codes are benchmarked against each other by comparing simulation results in the case of ion temperature gradient driven turbulence, in the adiabatic electron response limit. The two codes are the Eulerian code GENE and the Lagrangian particle-in-cell code ORB5 which solve the gyrokinetic equations. Linear results are presente...

The scaling of turbulence-driven heat transport with system size in magnetically confined plasmas is reexamined using first-principles based numerical simulations. Two very different numerical methods are applied to this problem, in order to resolve a long-standing quantitative disagreement, which may have arisen due to inconsistencies in the geome...

The ion temperature gradient (ITG) mode in the high wavenumber regime (k y q s > 1), referred to as short wavelength ion temperature gradient mode (SWITG) is studied using the nonlinear gyrokinetic electromagnetic code GENE. It is shown that, although the SWITG mode may be linearly more unstable than the standard long wavelength (k y q s < 1) ITG m...

The available computer power is the most important constraint limiting the horizontal resolution, the complexity of the model system, and the number of ensemble members of numerical weather prediction and regional climate models. In order to leverage future supercomputers, which will tend to have an increasing number of compute cores with reduced m...

Using the Eulerian code GENE [1], gyrokinetic simulations of microturbulence were carried out under conditions relevant to electron-Internal Transport Barriers (eITB) in the TCV tokmak [2], generated under conditions of low or negative shear. For typical density and temperature gradients measured in such barriers, the corresponding simulated fluctu...

The Eulerian gyrokinetic turbulence code gene has recently been extended to a full torus code. Moreover, it now provides Krook-type sources for gradient-driven simulations where the profiles are maintained on average as well as localized heat sources for a flux-driven type of operation. Careful verification studies and benchmarks are performed succ...

We investigate the redistribution of the neutral beam driven current in the presence of small scale turbulence in the ITER steady-state scenario. Gyrokinetic simulations show that anomalous transport of beam ions can be larger than collisional estimates. The impact on the beam driven current in ITER is studied with a single particle following code....

Important steps towards the understanding of turbulent transport have been made with the development of the gyrokinetic framework for describing turbulence and with the emergence of numerical codes able to solve the set of gyrokinetic equations. This paper presents some of the main recent advances in gyrokinetic theory and computing of turbulence....

In order to better identify the role of the magnetic topology on ITG and TEM instabilities, different MHD equilibria with increasing complexity are calculated using the CHEASE code [1]. We start from the geometry of the s-alpha cyclone benchmark case [2], consider the corresponding circular numerical equilibrium, and then successively add a non zer...

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. Thi...

Modelling of microturbulence-driven transport of energetic ions in an ITER steady-state scenario is presented. Results indicate that a significant fraction of the velocity space distribution of alpha particles and deuterium ions can be transported above neoclassical predictions. Turbulent magnetic fluctuations are found to significantly enhance the...

In magnetically confined fusion devices, the energy and particle transport is significantly larger than expected from purely collisional processes. This degraded confinement mostly results from small-scale turbulence and prevents from reaching self-sustained burning plasma conditions in present day experiments. A better understanding of these nonli...

Development and Benchmarking of the Global Gyrokinetic Code GENE

In order to address non-local effects in turbulent transport of magnetic-fusion devices, the gyrokinetic code GENE has been extended from a flux tube to a more global geometry. This global version of GENE includes radial variations of temperature and density profiles, as well as of magnetic equilibrium quantities. Non-periodic radial boundary condi...

We investigate the transport of fast ions in the presence of electromagnetic turbulence in an ITER steady state scenario. Linear and nonlinear analyses are carried out focusing on the transport features of passive deuterium. It is shown that the anomalous diffusion of NBI ions in ITER can become important. In particular the neutral beam driven curr...

In the context of gyrokinetic flux-tube simulations of microturbulence in magnetized toroidal plasmas, different treatments of the magnetic equilibrium are examined. Considering the Cyclone DIII-D base case parameter set [Dimits , Phys. Plasmas 7, 969 (2000)], significant differences in the linear growth rates, the linear and nonlinear critical tem...

The effect of plasma shape on confinement has been experimentally explored in the TCV tokamak revealing that the core electron heat transport is significantly reduced by a negative triangularity configuration, which could indicate a (partial) stabilization of the microinstabilities at play in a conventional positive triangularity configuration. Thi...

ulations are carried out with the flux tube version of the GENE code (2, 3) with the aim of analyzing a TCV shot for which an electron internal transport barrier (eITB) was obtained. Starting from experimentally relevant parameters, scans in the density and ion temperature gra- dient are carried out in order to investigate their influence on partic...

Using an interface with the ideal MHD equilibrium code CHEASE, numerical simulations are performed in realistic Tokamak geometry with the gyrokinetic flux tube code GENE [1, 2]. As a starting point in view of a more general study of geometrical effects on various types of micro‐turbulence, elongation and triangularity scans are carried out in the I...

The radial redistribution of energetic ions by background turbulence is investigated by means of linear and nonlinear gyrokinetic simulations with the GENE code [T. Dannert and F. Jenko, Phys. Plasmas 12, 072309 (2005)]. The fast particles are described by an asymmetric and anisotropic Maxwellian distribution function, and they are treated as passi...

The unique flexibility of TCV in plasma shaping has been exploited to address different aspects of tokamak physics in which the plasma shape may play a role. This paper summarizes the experiments undertaken in the TCV tokamak ("Tokamak à Configuration Variable") over the last decade in stability and transport and offers a comprehensive and integrat...

World research in magnetic fusion is aiming at the scientific and technological demonstration of an environmentally benign, virtually inexhaustible source of primary energy. The recent decision to proceed with the ITER project is an important milestone. This project is based on the tokamak concept, which as of today is the most advanced for the con...

Micro-instabilities, such as Ion Temperature Gradient modes (ITG) and Collisionless Trapped Electrons Modes (CTEM), are commonly held responsible for anomalous transport observed in tokamaks. While there have been a wide range of nonlinear studies on ITG turbulence, very little is known about the nonlinear physics of CTEM. This work presents the fi...

Experimental evidence of shaping effects, and especially triangularity, on heat transport coefficients [1, 2] were found on the TCV Tokamak. • Extension of the gyrokinetic flux tube code GENE [3, 4] from s−alpha approximation to general axisymmetric geometry using an interface with an ideal MHD equilibrium code, CHEASE [5].