April 15-17

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Author: Tariq Rafiq
Requested Type: Poster
Submitted: 2019-02-21 14:39:56

Co-authors: S. KAYE, W. GUTTENFELDER, J. ANDERSON, J. WEILAND, A.Y. PANKIN

Contact Info:
Lehigh University
19 Memorial Drive West
Bethlehem, Pennsylvan   18015
USA

Abstract Text:
Recently, a new unified fluid/kinetic microtearing mode model (MTM) was developed [1] and incorporated into the Multi-Mode Model (MMM) [2]. The MTM model has reproduced many linear gyrokinetic results for the NSTX discharges, such as the variation of real frequency and growth rates with poloidal wavenumber, beta, electron temperature, and density gradients. A particularly important result is that the model recovers the non-monotonic dependence of linear MTM growth rate with collision frequency [3]. The model is found to agree with experiment at high collisionality, but overpredicts the transport at low collisionality, predicting too low electron temperature profile. A way to improve the model for the low collisionality discharges is identified. The expression for electron thermal diffusivity is updated with a more general form of Rechester-Rosenbluth expression, which takes into account the dependence of the magnetic diffusivity on the magnetic correlation length. The previous expression for the electron thermal diffusivity was based on the collisional form of the stochastic transport Rechester-Rosenbluth model, which yields unphysically large values of diffusivity at low collisionalities. The results obtained with the improved MTM model are presented illustrating the degree to which the improved model yields electron temperature profiles that are consistent with low collisionality NSTX discharges.

*This work is supported by the U.S. Department of Energy, Office of Science, under Award Number DE-SC0013977, DEFG02-92-ER54141 and DE-AC02-09CH11466.

[1] T. Rafiq, et al., Phys. Plasmas 23, 062507 (2016)
[2] T. Rafiq et al., Phys. Plasmas 20, 032506 (2013)
[3] T. Rafiq et al., Effects of microtearing modes on the evolution of electron temperature profiles in high collisionality NSTX discharges, TH/P5-10, 27th IAEA Fusion Energy Conference, Gandhinagar, India, October 22-27 (2018)

Comments:
Teaching a class on Tuesday, April 16 in the morning. I appreciate if I will be allowed to present a poster on either April 15 or April 17.