Article

# System Size Effects on Gyrokinetic Turbulence

Centre de Recherches en Physique des Plasmas, Association Euratom-Confédération Suisse, Ecole Polytechnique Fédérale de Lausanne, PPB, 1015 Lausanne, Switzerland.

Physical Review Letters (Impact Factor: 7.73). 12/2012; 105:155001. DOI: 10.1103/PHYSREVLETT.105.155001 Source: OAI

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**ABSTRACT:**Reliable predictive simulation capability addressing confinement properties in magnetically confined fusion plasmas is critically-important for ITER, a 20 billion dollar international burning plasma device under construction in France. The complex study of kinetic turbulence, which can severely limit the energy confinement and impact the economic viability of fusion systems, requires simulations at extreme scale for such an unprecedented device size. Our newly optimized, global, ab initio particle-in-cell code solving the nonlinear equations underlying gyrokinetic theory achieves excellent performance with respect to \textquotedblleft time to solution at the full capacity of the IBM Blue Gene/Q on 786,432 cores of Mira at ALCF and recently of the 1,572,864 cores of Sequoia at LLNL. Recent multithreading and domain decomposition optimizations in the new GTC-P code represent critically important software advances for modern, low memory per core systems by enabling routine simulations at unprecedented size (130 million grid points ITER-scale) and resolution (65 billion particles).Proc. ACM/IEEE Conf. on Supercomputing (SC), Denver, CO; 11/2013 -
##### Article: Non-Linear Gyrokinetic Simulations of Microturbulence in TCV Electron Internal Transport Barriers

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**ABSTRACT:**Using the Eulerian code GENE [1], gyrokinetic simulations of microturbulence were carried out under conditions relevant to electron-Internal Transport Barriers (eITB) in the TCV tokmak [2], generated under conditions of low or negative shear. For typical density and temperature gradients measured in such barriers, the corresponding simulated fluctuation spectra appears to simultaneously contain longer wavelength Trapped Electron Modes (TEM, for typically k_perp*rho_i < 0.5, k_perp being the characteristic perpendicular wavenumber and rho_i the ion Larmor radius) and shorter wavelength Ion Temperature Gradient modes (ITG, k_perp*rho_i > 0.5). The contributions to the electron particle flux from these two types of modes are respectively outward/inward and may cancel each other out for experimentally realistic gradients. This mechanism may partly explain the feasibility of eITBs. The non-linear simulation results confirm the predictions of a previously developed quasi-linear model [3], namely that the stationary condition of zero particle flux is obtained through the competitive contributions of ITG and TEM. Parameter scans of gyrokinetic microturbulence simulations were carried out with an attempt to identify combinations of density and electron/ion temperature gradients which not only cancel out particle fluxes but minimize electron heat fluxes as well.Plasma Physics and Controlled Fusion 12/2011; 53:054011. · 2.37 Impact Factor

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