(TH/P8-1) Cross-field Transport Driven by Turbulent Scattering of Particles in Tokamaks

G.S. Xu1), S.Y. Ding1), W. Zhang1), B.N. Wan1), W. Fundamenski2)
1) Institute of Plasma Physics, Chinese Academy of Sciences, Hefei, China
2) Euratom/UKAEA Fusion Association, Culham Science Centre, Abingdon, OX14 3DB, UK

Abstract.  Some interesting observations from the recent massive particle simulation of the electron temperature gradient mode turbulence indicated that the mechanism underlying anomalous electron transport is the kinetic wave-particle decorrelation rather than the fluid eddy mixing. [Lin, Z, et al., Phys. Rev. Lett. 99 (2007) 265003] Long streamers, close to the pressure gradient scale length, are observed in this simulation. However, the transport didn't show dependence on the streamer length, but is proportional to the local fluctuation intensity. In tokamak sheared magnetic field, there is a percentage of electrons are trapped in the potential patterns of electrostatic turbulence, and their unperturbed orbits follow pendulum motion. These potential patterns constitute phase-space islands. The overlapping of islands not only takes place in velocity space but also in configuration space, due to the presence of densely packed mode rational surfaces in the tokamak configuration. The overlapping of adjacent phase-space islands leads to the formation of chaotic region near the separatrix of the islands. As a result, the particle performs random walk process in phase space and during this process irreversible scattering process takes place. This mechanism induces a Brownian diffusion in configuration space as well as velocity space, with a time scale determined by the resonant scattering time. In this paper, this transport mechanism is formulated using nonlinear drift kinetic equations and resonance broadening theory. It is indicated that the nonadiabatic response of the wave-trapped electrons induced by the resonant scattering process is an important dissipation mechanism underlying anomalous electron transport in tokamak plasmas.

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