Author: Silvia Espinosa
Requested Type: Pre-Selected Invited
Submitted: 2016-02-12 14:57:57
Co-authors: Peter J. Catto
Plasma Science and Fusion Center (PSFC-MIT)
77 Massachusetts Av
Cambridge, MA 02139
Significantly stronger impurity density in-out poloidal asymmetries than predicted by the most comprehensive neoclassical models have been measured in H-mode tokamaks pedestals during the last decade . However, these theories neglect the impurity diamagnetic drift compared to the ExB drift, while recent measurements  indicate that they can be of the same order. Retaining both impurity drifts for the first time, the stronger impurity density gradient required leads to the need to keep radial impurity flow, when evaluating the Pfirsch-Schluter parallel impurity flow from the continuity equation. The resulting modification in the impurity friction with banana regime ions in the parallel impurity momentum equation then allows stronger poloidal variation of the impurity density and the radial electric field without appealing to an anomalous mechanism. Whether the strong poloidal variation permitted explains the observations depends sensitively on two ratios: (i) the impurity over main ion diamagnetic drifts and (ii) the main ion poloidal flow over the main ion diamagnetic drift.
 R.M.Churchill et al.,Phys Plasmas 22,056104
 C.Theiler et al.,Nucl Fusion 54,083017
Supported by DOE Grant DE-FG0291ER54109 and La Caixa Fellowship.
EPS Poster Prize 2015