Parallelization on a Hybrid Architecture of GBS, a Simulation Code for Plasma Turbulence at the Edge of Fusion Devices

We present recent developments of GBS, a simulation code used to evolve plasma turbulence in the edge of fusion devices. GBS solves a set of 3D fluid equations, the Poisson and the Ampere equation, and a kinetic equation for the neutral atoms. Investigations carried out with GBS have significantly advanced our understanding of the plasma dynamics at the edge of fusion devices. For example, GBS simulations allowed the identification of the turbulent regimes and the saturation mechanisms of the linearly unstable modes. In GBS, a 3D Cartesian MPI communicator is employed, leading to excellent parallel scalability up to 8192 cores. To efficiently exploit many-core and hybrid architectures, new schemes using MPI+OpenMP and MPI+OpenACC have been recently implemented. We show the implementation of the new parallelization schemes, their scalability, and their efficiency. The new parallelization allows the efficient use of advanced hybrid supercomputers, such as Piz Daint at CSCS

An approximate single fluid 3-dimensional magnetohydrodynamic equilibrium model with toroidal flow

An approximate model for a single fluid three-dimensional (3D) magnetohydrodynamic (MHD) equilibrium with pure isothermal toroidal flow with imposed nested magnetic flux surfaces is proposed. It recovers the rigorous toroidal rotation equilibrium description in the axisymmetric limit. The approximation is valid under conditions of nearly rigid or vanishing toroidal rotation in regions with significant 3D deformation of the equilibrium flux surfaces. Bifurcated helical core equilibrium simulations of long-lived modes in the MAST device demonstrate that the magnetic structure is only weakly affected by the flow but that the 3D pressure distortion is important. The pressure is displaced away from the major axis and therefore is not as noticeably helically deformed as the toroidal magnetic flux under the subsonic flow conditions measured in the experiment. The model invoked fails to predict any significant screening by toroidal plasma rotation of resonant magnetic perturbations in MAST free boundary computations

Recent progress in the upgrade of the TCV EC-system with two 1MW/2s dual-frequency (84/126GHz) gyrotrons

The upgrade of the EC-system of the TCV tokamak has entered in its realization phase and is part of a broader upgrade of TCV. The MW-class dual-frequency gyrotrons (84 or 126GHz/2s/1MW) are presently being manufactured by Thales Electron Devices with the first gyrotron foreseen to be delivered at SPC by the end of 2017. In parallel to the gyrotron development, for extending the level of operational flexibility of the TCV EC-system the integration of the dual-frequency gyrotrons adds a significant complexity in the evacuated 63.5mm-diameter HE11 transmission line system connected to the various TCV low-field side and top launchers. As discussed in [1], an important part of the present TCV-upgrade consists in inserting a modular closed divertor chamber. This will have an impact on the X3 top-launcher which will have to be reduced in size. For using the new compact launcher we are considering employing a Fast Directional Switch (FADIS), combining the two 1MW/126GHz/2s rf-beams into a single 2MW rf-beam

Design studies of the dual-frequency operation of the W7-X/140GHz/1MW gyrotron at 126GHz for TCV and 168GHz for ITER

A detailed study of the operational capabilities of the W7-X/1MW gyrotron operated at 126GHz/TE26,7 is presented. This study is associated with the foreseen upgrade of TCV in which it is planned to add to the present EC system 3MW of additional RF power bringing the total EC-power to 7.5MW. This study is extended to a possible operation of the gyrotron at the ITER relevant frequency of 168GHz in the TE35,9 mode without implementing any further modification neither in the gyrotron nor in the gyrotron superconducting magnet

APPLICATION DEDICATED CLUSTERING

L’adaptation de grappes aux besoins des applications est démontrée utilisant un programme en production de type Car-Parrinello. Pour ce faire, l'application et la grappe de processeurs sont parametrisées ce qui donne la possibilité d’une prédiction a priori du système de communication de la grappe. Une comparaison entre les performances prédites et mesurées sur Swiss-T1 valide la théorie. By means of a first principles chemistry Car-Parrinello program, it is shown that commodity clusters can be tailored to applications. For this purpose, a parameterisation of the applications and the parallel machines is made that enables an a-priori prediction of the application behaviour on a given cluster, or, inversely, of an applicationdedicated cluster design. Comparisons between predicted and measured performance results on the Swiss-T1 cluster support the theory

Evaluation of experimentally measured non-stationary oscillations in gyrotrons using adequate simulation methods

In order to properly simulate cases in which gyrotrons exhibit fast temporally varying oscillations, such as non-stationary oscillations or possible dynamic After-Cavity Interaction (ACI), an adequate model for the beam-wave interaction has to be used. We will show that the commonly used assumption of considering a constant wave-field envelope during the electron transit time has to be abandoned. The appropriate model (reduced 1D Particle-In-Cell (PIC) model) is briefly presented and the implications of using an inadequate model are illustrated. For the case of a 150W/260GHz gyrotron, non-stationary simulations with the new model will be compared to experiment and used in order to investigate the underlying mechanism of these oscillations

Towards an Intelligent Grid Scheduling System

The main objective of the Intelligent GRID Scheduling System (ISS) project is to provide a middleware infrastructure allowing a good positioning and scheduling of real life applications in a computational GRID. According to data collected on the machines in the GRID, on the behaviour of the applications, and on the performance requirements demanded by the user, a heuristic cost function is evaluated by means of which a well suited computational resource is detected and allocated to execute his application. The monitoring information collected during execution is put into a database and reused for the next resource allocation decision. In addition to providing scheduling information, the collected data allows to detect overloaded resources and to pin-point inefficient applications that could be further optimised

Global simulations of tokamak microturbulence: finite beta effects and collisions

In this paper, we present global nonlinear gyrokinetic simulations including finite beta effects and collisions in tokamak geometry. Global electromagnetic simulations using conventional delta-f particle in cell methods are very demanding, with respect to numerical resources, in order to correctly describe the evolution of the non-adiabatic part of the electron distribution function. This difficulty has been overcome using an appropriate adjustable control variate method in the conventional delta-f scheme. Linearized inter-species and like-species collision operators have also been introduced in the model. The inclusion of the collisional dynamics makes it possible to carry out simulations of microturbulence starting from a global neoclassical equilibrium and to study the effect of collisions on the transport induced by electrostatic microinstabilities