Running simultaneous Kepler sessions for the parallelization of parametric scans and optimization studies applied to complex workflows

In 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 (ITM) platform developed by the Nuclear Fusion community within the context of EUROFusion project [1]. 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 a 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.