Author: Paolo Ricci
Requested Type: Pre-Selected Invited
Submitted: 2018-02-28 09:58:54
Co-authors: C.F. Beadle, F.D. Halpern, J. Loizu, A. Mosetto, P. Paruta, F. Riva, C. Wersal
Swiss Plasma Center, EPFL
Understanding the behaviour of the fusion fuel in the SOL region is a crucial step on the way to fusion energy. For example, the SOL dynamics determine the heat load to the tokamak vessel walls – a showstopper for the whole fusion program if material requirements cannot be met. With the goal of improving our understanding of the SOL dynamics, the GBS code was developed during the past years . GBS simulates the SOL plasma turbulence by solving the drift-reduced Braginskii equations self-consistently with the kinetic neutral atom dynamics . The simulations evolve the SOL dynamics as it results from the plasma outflowing from the core, turbulent transport, plasma losses and recycling at the walls. Simulations with realistic tokamak parameters can be performed. Thanks to GBS simulation results, the instabilities driving transport were identified  as well as the turbulence saturation mechanisms  and the role of velocity shear in suppressing turbulence . Plasma current circulation and toroidal rotation mechanisms at play in the SOL were clarified . These advances have led to a first principles scaling of the SOL width  and to the understanding of the physics mechanisms responsible for the narrow feature observed in the proximity of the last closed flux surface  (an observation that led to the redesign of the ITER first wall). We will present an overview of our simulation and theoretical results, as well as their comparison with experimental measurements from several tokamaks worldwide.  Ricci et al, Plasma Phys. Contr. Fusion 54, 124047; Halpern et al, J. Comp. Phys. 315, 388.  Wersal and Ricci, Nucl. Fusion 57, 116018.  Mosetto et al, Phys. Plasmas 20, 092308.  Ricci and Rogers, Phys. Plasmas 20, 010702.  Halpern and Ricci, Nucl. Fusion 57, 034001.  Loizu et al, J. Plasma Phys. 83, 575830601; Loizu et al, Phys. Plasmas 21, 062309.  Halpern et al, Nucl. Fusion 53, 122001; Halpern et al, Nucl. Fusion 54, 043003.