Microtearing instabilities and electron thermal transport in low and high collisionality NSTX discharges
T. Rafiq, S. Kaye, W. Guttenfelder, J. Weiland, E. Schuster, J. Anderson, and L. Luo
Physics of Plasmas 28, 022504 (2021).
Abstract
|
|
Microtearing mode (MTM) real frequency, growth rate, magnetic fluctuation
amplitude, and resulting electron thermal transport are studied in
systematic NSTX scans of relevant plasma parameters. The dependency of
the MTM real frequency and growth rate on plasma parameters, suitable
for low and high collision NSTX discharges, is obtained by using the
reduced MTM transport model [T. Rafiq et al., Phys. Plasmas 23, 062507 (2016)].
The plasma parameter dependencies are compared and found to be consistent
with the results obtained from MTM using the gyrokinetic GYRO code.
The scaling trend of collision frequency and plasma beta is found to be
consistent with the global energy confinement trend observed in the NSTX
experiment. The strength of the magnetic fluctuation is found to be
consistent with the gyrokinetic estimate. In earlier studies, it was
found that the version of the multi-mode (MM) anomalous transport model,
which did not contain the effect of MTMs, provided an appropriate
description of the electron temperature profiles in standard tokamak
discharges and not in spherical tokamaks. When the MM model, which involves
transport associated with MTMs, is incorporated in the TRANSP code and
is used in the study of electron thermal transport in NSTX discharges,
it is observed that the agreement with the experimental electron
temperature profile is substantially improved.