Search for the Missing L-mode Edge Transport and Possible Breakdown of Gyrokinetics

While GYRO simulations of typical core ($0 < r/a < 0.7$) DIII-D L-modes seems to be in good agreement with experiment, simulated low-k ($k_\theta\rho_s < 1$) transport and turbulence intensity is more than 5-fold lower than experimentally inferred levels in the near edge L-mode ($r/a=0.7-0.95$) DIII-D shot 128913 [1]. Global edge slice GYRO simulations of this and the well-studied discharge 101391 [2] are presented here to document the shortfall. TGLF transport code simulations over a large L-mode database indicate this short fall is not atypical so that L-mode edges transit to H-like pedestal profiles contrary to experiment. High edge e-i collisionality stabilizes the TEM modes so that diffusivities ($\chi$) decrease like $T^{7/2}/n$ to the cold edge. The very high magnetic shear and density gradients stabilize the ITG despite the very high temperature gradient drive and high $q$. High-$k$ ETG can make-up for the shortfall in the electron but increases ion transport very little. Near L-edge transport is highly local. Focusing on local simulations at $r/a=0.9$, the ion channel short fall can exceed 10-fold. An artificial 10-fold increase in collisionality is needed to reach the expected resistive g-mode scaling with $\chi$ increasing like $nT^{-1/2}$. Identical GYRO drift kinetic ion simulations (suppressing the gyroaverage) are close to experiment levels suggesting a possible breakdown of low-frequency gyrokinetics. Formulation of a nonlinear theory of 6D drift-cyclotron kinetics following the fast time scale of the gyrophase to test the breakdown of 5D gyrokinetics with reduced model simulations is presented.\par \vskip6pt \noindent [1] C.\ Holland, A.E.\ White, {\em et al.}, Phys.\ Plasmas {\bf 16}, 052301 (2009).\par \noindent [2] R.E.\ Waltz, J.\ Candy, C.C.\ Petty, Phys.\ Plasmas {\bf 13}, 072304 (2006).