2-dimensional kinetic studies of the fusion plasma edge

Modeling of the tokamak Scrape-off Layer (SOL) represents one of the most challenging tasks in fusion plasma study. The SOL influences the particle, the momentum and the energy fromo plasma core, so that affecting the overall plasma discharge in fusion devices. This study is especially actual for optimizing of the design of next generation tokamak ITER, where estimations of power loads to the Plasma Facing Components (PFC) during the so called Edge-Localized Modes (ELM) and of tritium retention are still unsolved problems. The aim of the proposed project is to develop a fully kinetic 2-dimensional model of the SOL, which will include nonlinear dynamics of plasma, impurity and neutral particles, as well as nonlinear model of plasma-surface interactions. This (to our knowledge) unique task will require collection of appropriate atomic, molecular and plasma-surface interaction data, development of corresponding optimized Monte Carlo routines and implementation of highly scalable 2-dimensional Poisson equation solvers. Full self-consistency of the model can be achieved by "absolute" resolution of particle motion in space and time (down to electron gyroradii), as a result this code has to be optimized for running on High Performance Computing facilities. This new model will be applied for interpretive and predictive simulations of the existing tokamak, as well as for predictive simulations of the ITER SOLs. Main efforts will be denoted to studying of power loads to the PFC during the ELMs and tritium retention rates, as well as to quantifying of kinetic effects for their implementation in SOL simulating fluid code packages like B2-SOLPS, EDGE2D and so on. We hope that the results obtained in this project will contribute to further optimization of the design of ITER as well as of after-ITER machines (like DEMO). The 2-dimensional kinetic code developed in this project will represent a powerful tool for studying of fully and partially ionized plasmas. It can be used practically in any branch of plasma physics starting from low temperature laboratory plasma till astrophysical plasma. We intend to perform this project in collaboration with our colleagues in Austria, EU, Japan and USA.

Plasma is a fourth state of matter. It represents 99.9% of the visible universe: the stars, the interstellar and the intergalactic space consist of plasma. On the earth there exists the natural (e.g. the flame) as well as man-made plasma (e.g. lighting lamps, different plasma devices). The plasma devices are used in different technological processing, or represent test fusion facilities helping to design future thermonuclear fusion reactors (also representing plasma devices). Thermonuclear fusion is the energy source of the stars where nucleus of light elements like a deuterium and a tritium fuse together and release a huge amount of energy. The thermonuclear fusion reactors will use this source and provide the cleanest and safest energy for mankind. The plasma in plasma devices consists of the core and edge plasmas. The later is formed in front of chamber wall and affects plasma particle and power fluxes from/into the chamber wall. As a result, the plasma edge can strongly influence and sometimes even define the properties of the whole plasma in the device. Especially important the plasma edge, or as it called the Scrape-off Layer (SOL), for so called Magnetic confinement fusion devices. The SOL strongly influences the content and performance of the core plasma as well as the lifetime of chamber elements. Hence, the SOL study has become one of the hottest topics in fusion-relevant plasma research. The SOL consists of electrons and main ions, neutrals and impurity ions, and dust particles. They are not in thermal equilibrium and interact in an inelastic way with each other and with the chamber wall. The SOL research requires interdisciplinary study, which can only performed via sophisticated numerical tools. The aim of this project was the development of multidimensional numerical codes for precise modelling of the SOL. These codes, BIT1 and BIT2, represent at present probably the most advanced kinetic codes for SOL simulations. They run on massively parallel platform, i.e. the use hundreds and thousands of processors in an optimized way; include few tens of different particle species and nonlinear interaction between them, as well as with the chamber wall. Codes are very flexible against implementation of new particle types and new physics. Using our codes we perform different sets of plasma edge simulations and demonstrate that number of well-known plasma characteristics are not valid for the SOL and have to be revised. In some cases, such as the propagation of the ion sound waves, the thermal force acting on highly charged impurity particles, the structure of plasma particle velocity distribution functions and so on, we explain these effects and developed the corresponding new models. We expect that our results will contribute to designing and optimization of test magnetic confinement fusion devices as well as future reactors.