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Inhaltsangabe zu "Development and Application of a Multiscale Model for the Magnetic Fusion Edge Plasma Region"
a decisive role for the performance and lifetime of a magnetic fusion reactor. For
the particles, classical and neoclassical theories underestimate the associated radial
transport by at least an order of magnitude. Drift fluid models, including mesoscale
processes on scales down to tenths of millimeters and microseconds, account for the
experimentally found level of radial transport; however, numerical simulations for
typical reactor scales (of the order of seconds and centimeters) are computationally
very expensive. Large scale code simulations are less costly but usually lack an
adequate model for the radial transport.
The multiscale model presented in this work aims at improving the description of
radial particle transport in large scale codes by including the effects of averaged
local drift fluid dynamics on the macroscale profiles. The multiscale balances are
derived from a generic multiscale model for a fluid, using the Braginskii closure
for a collisional, magnetized plasma, and the assumptions of the B2 code model
(macroscale balances) and the model of the local version of the drift fluid code ATTEMPT
(mesoscale balances). A combined concurrent–sequential coupling procedure
is developed for the implementation of the multiscale model within a coupled code
system. An algorithm for the determination of statistically stationary states and
adequate averaging intervals for the mesoscale data is outlined and tested, proving
that it works consistently and efficiently.
The general relation between mesoscale and macroscale dynamics is investigated
exemplarily by means of a passive scalar system. While mesoscale processes are
convective in this system, earlier studies for small Kubo numbers K 1 have
shown that the macroscale behavior is diffusive. In this work it is demonstrated
by numerical experiments that also in the regime of large Kubo numbers K 1
the macroscale transport remains diffusive. An analytic expression for the diffusion
coefficient D is found, being consistent with results from percolation theory