Kinetic studies of magnetized edge plasmas

Developing and improving analytical and numerical tools for predictive analysis of plasma confinement in a next- generation fusion experimental facility of the tokamak type (ITER) are of primary importance for fusion research and, hence, for mankind`s long-term energy supply. In particular, the study of fusion edge plasmas has attracted growing interest in recent years. By fusion edge plasmas we mean the region outside the last closed magnetic surface (separatrix) - i.e., the scrape-off-layer (SOL) -, however with inclusion of and special emphasis on its boundaries with the material walls and the separatrix region. The SOL strongly influences and even controls the particle and energy fluxes from and to the core plasma, thus playing a crucial role for the overall plasma confinement. As of today, the main tools for realistic SOL studies are large fluid codes such as B2-SOLPS, EDGE2D and UEDGE. However, in SOL plasmas there are a number of processes which cannot be described by fluid codes but rather require genuinely kinetic treatments - which, however, are often nonexistent or insufficiently developed as of today. To contribute to filling this severe gap, the present project, whose duration is envisaged to be 2.5 years, aims at achieving the following goals: (1) A comprehensive, self-consistent kinetic description of the plasma-wall transition (PWT) region near material walls will be formulated with realistic assumptions and in great generality. This will include (a) fundamental research on the PWT, and (b) formulation of boundary conditions for fluid (and gyro-kinetic codes) at the tokamak divertors. For each problem, the conceptual theoretical work required will be accompanied by adequate sets of simulation runs with input parameters relevant to existing and planned tokamaks. (2) Systematic kinetic simulations of the SOL will be performed for a number of existing tokamaks (TCV, ASDEX Upgrade and JET) and future ones (ITER). This will include (a) aspects of the transport in the time-independent ELM-free SOL, (b) study of heat propagation in the ELMy SOL and corresponding heat and particle loads on the divertor plates, (c) calculation of particle, momentum and heat flux limiters for various tokamak operational regimes, such as, L-mode, ELM-free or ELMy H-modes, (d) extension of existing kinetic simulation codes (mainly BIT1 and BIT2) with the aim of increasing the realism of SOL simulations and including two-dimensional effects, and (e) formulation of realistic boundary conditions at the separatrix, thus placing the SOL more explicitly than hitherto into the framework of Integrated Tokamak Modelling (ITM). In the appropriate places, first attempts will be made at simultaneously including, in kinetic description, transport components parallel and perpendicular to the magnetic field. The present project is intended to be the crowning achievement on top of several years of pertinent analytical and numerical investigations, which were carried to a large extent by the previous FWF projects P12477-TPH ("Particle-simulation studies of divertor plasmas``, 1998-2000) and P15013-N08 ("Kinetic studies of magnetized plasmas in contact with walls", 2001-04) and already by now have led to a significantly enhanced understanding of the magnetized PWT and the entire SOL. By making substantial new contributions - and, as previously, in close collaboration with a number of high-grade pertinent research groups around the world - it explicitly aims at filling the gaps still existing, thus arriving at a comprehensive, self-consistent kinetic picture not only of the magnetized PWT, but of the entire SOL and its role within the entire tokamak plasma (ITM). The results of this project should contribute significantly to the understanding, design and optimization of present-day and future tokamaks.

Developing and improving analytical and numerical tools for predictive analysis of plasma confinement in a next- generation fusion experimental facility of the tokamak type (ITER) are of primary importance for fusion research and, hence, for mankind`s long-term energy supply. In particular, the study of fusion edge plasmas has attracted growing interest in recent years. By fusion edge plasmas we mean the region outside the last closed magnetic surface (separatrix) - i.e., the scrape-off-layer (SOL) -, however with inclusion of and special emphasis on its boundaries with the material walls and the separatrix region. The SOL strongly influences and even controls the particle and energy fluxes from and to the core plasma, thus playing a crucial role for the overall plasma confinement. As of today, the main tools for realistic SOL studies are large fluid codes such as B2-SOLPS, EDGE2D and UEDGE. However, in SOL plasmas there are a number of processes which cannot be described by fluid codes but rather require genuinely kinetic treatments - which, however, are often nonexistent or insufficiently developed as of today. To contribute to filling this severe gap, the present project, whose duration is envisaged to be 2.5 years, aims at achieving the following goals: (1) A comprehensive, self-consistent kinetic description of the plasma-wall transition (PWT) region near material walls will be formulated with realistic assumptions and in great generality. This will include (a) fundamental research on the PWT, and (b) formulation of boundary conditions for fluid (and gyro-kinetic codes) at the tokamak divertors. For each problem, the conceptual theoretical work required will be accompanied by adequate sets of simulation runs with input parameters relevant to existing and planned tokamaks. (2) Systematic kinetic simulations of the SOL will be performed for a number of existing tokamaks (TCV, ASDEX Upgrade and JET) and future ones (ITER). This will include (a) aspects of the transport in the time-independent ELM-free SOL, (b) study of heat propagation in the ELMy SOL and corresponding heat and particle loads on the divertor plates, (c) calculation of particle, momentum and heat flux limiters for various tokamak operational regimes, such as, L-mode, ELM-free or ELMy H-modes, (d) extension of existing kinetic simulation codes (mainly BIT1 and BIT2) with the aim of increasing the realism of SOL simulations and including two-dimensional effects, and (e) formulation of realistic boundary conditions at the separatrix, thus placing the SOL more explicitly than hitherto into the framework of Integrated Tokamak Modelling (ITM). In the appropriate places, first attempts will be made at simultaneously including, in kinetic description, transport components parallel and perpendicular to the magnetic field. The present project is intended to be the crowning achievement on top of several years of pertinent analytical and numerical investigations, which were carried to a large extent by the previous FWF projects P12477- TPH ("Particle-simulation studies of divertor plasmas``, 1998-2000) and P15013-N08 ("Kinetic studies of magnetized plasmas in contact with walls", 2001-04) and already by now have led to a significantly enhanced understanding of the magnetized PWT and the entire SOL. By making substantial new contributions - and, as previously, in close collaboration with a number of high-grade pertinent research groups around the world - it explicitly aims at filling the gaps still existing, thus arriving at a comprehensive, self-consistent kinetic picture not only of the magnetized PWT, but of the entire SOL and its role within the entire tokamak plasma (ITM). The results of this project should contribute significantly to the understanding, design and optimization of present-day and future tokamaks.