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(TH/1-3) Full Radius Linear and Nonlinear Gyrokinetic Simulations for Tokamaks and Stellarators: Zonal Flows, Applied ExB Flows, Trapped Electrons and Finite Beta

L. Villard¹⁾, S.J. Allfrey¹⁾, A. Bottino¹⁾, M. Brunetti¹⁾, G.L. Falchetto⁴⁾, V. Grandgirard⁴⁾, R. Hatzky²⁾, J. Nuhrenberg³⁾, A.G. Peeters²⁾, O. Sauter¹⁾, S. Sorge³⁾, J. Vaclavik^1)
 
1) CRPP, Association Euratom-Suisse, EPFL, Lausanne, Switzerland
²⁾ Max-Planck-Institut für Plasmaphysik, Association Euratom-IPP, Garching, Germany
³⁾ Max-Planck-Institut für Plasmaphysik, Association Euratom-IPP, Greifswald, Germany
⁴⁾ DRFC, Association Euratom-CEA, Cadarache, France

Abstract.  Finite beta effects on microinstabilities are investigated with a linear global spectral electromagnetic gyrokinetic formulation. While the toroidal ITG mode is stabilized with increasing beta, another mode of electromagnetic nature becomes unstable below the ideal MHD ballooning limit. Its unique global structure is shown for the first time. The weakly destabilizing effect of trapped electron dynamics on ITG modes is shown for the first time in an axisymmetric bumpy configuration. Applied ExB flows in tokamak and heliac configurations stabilize toroidal and helical ITG modes with a quadratic dependence on the shearing rate. Trapped particle modes can be destabilized by ExB flows. Self-generated zonal flows are studied with a global nonlinear electrostatic formulation that retains parallel nonlinearity and thus allows for a check of the energy conservation property. A quasi steady-state is reached with zonal flow shearing rates fluctuating around a value comparable to the linear growth rate of the most unstable ITG. A semi-Lagrangian approach free of statistical noise is proposed as an alternative to the nonlinear PIC $\delta_{f}^{}$ formulation.

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