The ITER Integrated Modelling & Analysis Suite (IMAS) will support both plasma operation and research activities on the ITER tokamak experiment. The IMAS will be accessible to all ITER members as a key tool for the scientific exploitation of ITER. The backbone of the IMAS infrastructure is a standardized, machine-generic data model that represents simulated and experimental data with identical structures. The other outcomes of the IMAS design and prototyping phase are a set of tools to access data and design integrated modelling workflows, as well as first plasma simulators workflows and components implemented with various degrees of modularity.
Two different modes of electron heating are found in microwave discharges: the bulk heating mode characterized with low electron density n e and high electron temperature T e (∼10 eV), and the surface heating mode with high n e and low T e (∼3 eV). The correlation between the heating mode and the electron energy distribution function (EEDF) is qualitatively interpreted in terms of non-local kinetic theory, taking account of the ambipolar potential well. A biased optical probe diagnostics of a surface wave plasma (SWP) reveals that the surface heating mode gives a bi-Maxwellian type EEDF, that is, a sum of two Maxwellian distributions of bulk temperature T b and tail temperature T t > T b . On the other hand, the EEDF of inductively coupled plasma (ICP) is close to a single-Maxwellian distribution with electron temperature higher than the bulk temperature T b of the SWP. Such differences in the EEDFs make the composition of the reactive species of the two plasmas different; namely, ion and radical measurements at the same electron density show that the ICP contains more F radicals and less CF 3 and CF 2 radicals in comparison with the SWP. In addition, a simplified model based on the bi-Maxwellian EEDF shows how the EEDF determines the ion and radical compositions, supporting the major experimental results. These observations and calculations suggest that plasma chemistry is controllable by tailoring the EEDF with proper adjustment of bulk heating and/or surface heating of electrons.
The plasma flow in the scrape-off layer (SOL) plays an important role for the particle control in magnetic fusion reactors. The flow is expected to expel Helium ashes and to retain impurities in the divertor region, if it is directed towards the divertor plate. It has been experimentally observed, however, that the flow direction is sometimes opposite; from the plate side to the SOL middle side in the outer SOL region of tokamaks. A full particle code, PARASOL, is applied to a tokamak plasma with the upper-null-point (UN) or lower-nullpoint (LN) divertor configuration for the downward ion grad-B drift. PARASOL simulations for the medium aspect ratio reveal the variation of the flow pattern: For the UN case, the flow velocity V // parallel to the magnetic field is directed to the diverter plate both in the inner and outer SOL regions and the stagnation point (V // = 0) is located symmetrically at the bottom. On the other hand for the LN case, V // in the outer SOL region has a backward flow pattern. The stagnation point moves below the mid-plane of the outer SOL. These simulation results are very similar to the experimental results. Simulations are carried out by changing the aspect ratio and by artificially cutting the electric field. It is found that the banana motion of trapped ions is very important for the formation of the flow pattern in addition to the self-consistent electric field.
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