Effects of Microtearing Modes on the Evolution of Electron Temperature Profiles in High Collisionality NSTX Discharges
T. Rafiq, S. M. Kaye, W. Guttenfelder, A. Kritz, E. Schuster, J. Weiland, and F. M. Poli
27th IAEA Fusion Energy Conference
Gandhinagar, India, October 22-27, 2018
Abstract
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A goal of this research project is to describe the temporal evolution
of the electron temperature profiles in high collisionality NSTX H-mode
discharges. Gyrokinetic simulations indicate that microtearing modes
(MTMs) are a source of significant electron thermal transport in these
discharges. In order to understand the effect MTMs have on transport
and, consequently, on the evolution of electron temperature in NSTX
discharges, a reduced transport model for MTMs has been developed. The
dependence of the MTM real frequency and growthrate on plasma parameters,
appropriate for high collisionality NSTX discharges, is obtained employing
the new MTM transport model. The dependencies on plasma parameters are
compared and found to be consistent with MTM results obtained using the
gyrokinetic GYRO code. The MTM real frequency, growthrate, magnetic
fluctuations and resulting electron thermal transport are examined for
high collisionality NSTX discharges in systematic scans over the relevant
plasma parameters. In earlier studies it was found that the version of
the Multi-Mode (MM) transport model, that did not include the effect of
MTMs, provided a suitable description of the electron temperature profiles
in high collisionality standard tokamak discharges. That version of the
MM model included contributions to electron thermal transport from the
ion temperature gradient, trapped electrons, kinetic ballooning, peeling
ballooning, collisionless and collision dominated MHD modes, and electron
temperature gradient modes. When the MM model, that includes transport
associated with MTMs, is installed in the TRANSP code and is utilized
in studying electron thermal transport in high collisionality NSTX
discharges, it is found that agreement with the experimental electron
temperature profile is significantly improved.