Running Simultaneous Kepler Sessions for the Parallelization of Parametric Scans and Optimization Studies Applied to Complex Workflows

AbstractIn this paper we present an approach taken to run multiple Kepler sessions at the same time. This kind of execution is one of the requirements for Integrated Tokamak Modelling platform developed by the Nuclear Fusion community within the context of EUROFusion project[2]. The platform is unique and original: it entails the development of a comprehensive and completely generic tokamak simulator including both the physics and the machine, which can be applied for any fusion device. All components are linked inside workflows. This approach allows complex coupling of various algorithms while at the same time provides consistency. Workflows are composed of Kepler and Ptolemy II elements as well as set of the native libraries written in various languages (Fortran, C, C++). In addition to that, there are Python based components that are used for visualization of results as well as for pre/post processing. At the bottom of all these components there is a database layer that may vary between software releases, and require different version of access libraries. The community is using shared virtual research environment to prepare and execute workflows. All these constraints make running multiple Kepler sessions really challenging. However, ability to run numerous sessions in parallel is a must - to reduce computation time and to make it possible to run released codes while working with new software at the same time. In this paper we present our approach to solve this issue and examples that show its correctness

EUROfusion Integrated Modelling (EU-IM) capabilities and selected physics applications

International audienceRecent developments and achievements of the EUROfusion Code Development for Integrated Modelling project (WPCD), which aim is to provide a validated integrated modelling suite for the simulation and prediction of complete plasma discharges in any tokamak, are presented. WPCD develops generic complex integrated simulations, workflows, for physics applications, using the standardized European Integrated Modelling (EU-IM) framework. Selected physics applications of EU-IM workflows are illustrated in this paper

Influence of an external gas puff on the RI-mode confinement properties in TEXTOR

An actual subject of experimental and theoretical studies in present day fusion research is the development of an operational scenario combining simultaneously high confinement, with at least H-mode quality, and high densities, around or above the empirical Greenwald limit. Recently, this subject was studied in TEXTOR Radiative Improved (RI) mode discharges, in which the Seeding of a small amount of impurities is helpful in a transition to the improved confinement stage . It was found that by the careful tailoring of external fuelling and optimisation of the wall conditions it is possible to maintain the H-mode or even higher quality confinement at densities much above Greenwald density limit. However, more intense fuelling, aimed to extend maximal achievable densities, led to the progressive confinement deterioration. The theory explains the transition to the RI-mode as a bifurcation into the stage where the transport governed by the Ion Temperature Gradient (ITG) instability is significantly reduced due to a high density gradient and high value of the effective charge. The numerical studies of an influence of the gas puff intensity an confinement properties of plasma, done with the help of the 1-D transport code RITM, Show that the Same theory can be used for an explanation of the confinement rollover triggered by a strong gas puff. The code was modified in order to simulate the effect of the gas puff an the confinement properties. The anomalous transport coefficients in the plasma core include contributions from the ITG and Dissipative Trapped Electron (DTE) instabilities . The transport at the plasma edge under RI-mode conditions might be described by the electrostatic turbulence caused by electric currents in the scrape-off layer of the limiter. The present computations show that this assumption for the edge transport does not allow the modeling of an effect of the gas puff intensity an the profiles evolution in agreement with experimental observations . The level of the edge transport must be increased significantly in order to reproduce the evolution of the plasma density and the effective ion charge profiles during confinement degradation caused by a strong gas puff. An increase of this order is in agreement with reflectometer measurements and could tentatively be explained by the effect of neutrals an Drift Resistive Ballooning instability. Although, an increase of the edge transport is a necessary condition for the core confinement deterioration, the latter is produced by the resumption of ITG instability in the plasma core. The present studies show, that the reduction of impurity content of plasma and high positive time derivative of the density provided by a strong gas puff are crucial conditions for the restart of the ITG mode

Runaway electron modelling in the self-consistent core European Transport Simulator

Relativistic runaway electrons are a major concern in tokamaks. Although significant theoretical development had been undertaken in recent decades, we still lack a self-consistent simulator that could simultaneously capture all aspects of this phenomenon. The European framework for Integrated Modelling (EU-IM) facilitates the integration of different plasma simulation tools by providing a standard data structure for communication that enables relatively easy integration of different physics codes. A three-level modelling approach was adopted for runaway electron simulations within the EU-IM. Recently, a number of runaway electron modelling modules have been integrated into this framework. The first level of modelling (Runaway Indicator) is limited to the indication if runaway electron generation is possible or likely. The second level (Runaway Fluid) adopts an approach similar to e.g. the GO code, using analytical formulas to estimate changes in the runaway electron current density. The third level is based on the solution of the electron kinetics. One such code is LUKE that can handle the toroidicity-induced effects by solving the bounce-averaged Fokker-Planck equation. Another approach is used in NORSE, which features a fully nonlinear collision operator that makes it capable of simulating major changes in the electron distribution, for example slide-away. Both codes handle the effect of radiation on the runaway distribution. These runaway-electron modelling codes are in different stages of integration into the EU-IM infrastructure, and into the European Transport Simulator (ETS), which is a fully capable modular 1.5D core transport simulator. The ETS with Runaway Fluid was benchmarked to the GO code implementing similar physics. Coherent integration of kinetic solvers requires more effort on the coupling, especially regarding the definition of the boundary between runaway and thermal populations, and on consistent calculation of resistivity. Some of these issues are discussed

EUROfusion Integrated Modelling (EU-IM) capabilities and selected physics applications

International audienceRecent developments and achievements of the EUROfusion Code Development for Integrated Modelling project (WPCD), which aim is to provide a validated integrated modelling suite for the simulation and prediction of complete plasma discharges in any tokamak, are presented. WPCD develops generic complex integrated simulations, workflows, for physics applications, using the standardized European Integrated Modelling (EU-IM) framework. Selected physics applications of EU-IM workflows are illustrated in this paper