Jukka A. Heikkinen

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Direct measurements of micro-, meso-, and macroscale transport phenomena in the FT-2 tokamak are shown to be quantitatively reproduced by global full f nonlinear gyrokinetic simulation predictions. A detailed agreement with mean equilibrium E×B flows, oscillating fine-scale zonal flows, and turbulence spectra observed by a set of sophisticated microwave(More)
Monte Carlo ion simulation based on neoclassical radial current balance in a divertor tokamak gives a stationary sheared E 3 B flow. The neoclassical radial electric field Er shows no bifurcation in contrast with earlier orbit loss models, but the shear in Er reaches values at which a transition to enhanced confinement has been observed. Also, MHD(More)
Abstract A linear empirical threshold condition ωE×B/γITG > 0.68s − 0.095 has been found for the onset of the ion internal transport barriers in the JET optimised shear database. Here, s is the magnetic shear, ωE×B the flow shearing rate and γITG is an approximate of the linear growth rate of the ion temperature gradient instability. The present empirical(More)
Gyrokinetic particle-in-cell simulation on a transport and microinstability time scale is performed with the ELMFIRE code for a small tokamak FT-2 with kinetic electrons. Turbulent modes are characterized based on their poloidal phase velocity, and tentative comparison with the Doppler reflectometric measurement is done for the poloidal mode rotation.(More)
The orbit loss current is calculated for the ASDEX Upgrade geometry using the 5D (3D in configuration space and 2D in velocity space) Monte Carlo code ASCOT. The balance between the obtained current and the analytical estimate of the return current shows an L–H transition for the normalized collision frequency ν∗i ≈ 1 as expected from analytic theory. The(More)
Predictive transport simulations of tokamak discharges are continuously improving thanks to increasing computational resources available and to the efforts made in code development. As an example of the progress, a recent work [1] with the Elmfire code demonstrates the ability of global gyrokinetic full f electrostatic particle simulations, including both(More)