Nonlinear verification of a linear critical gradient model for energetic particle transport by Alfven eigenmodes
Here, a “stiff transport” critical gradient model of energetic particle (EP) transport by EPdriven Alfven eigenmodes (AEs) is verified against local nonlinear gyrokinetic simulations of a wellstudied beamheated DIIID discharge 146102. A greatly simplifying linear “recipe” for the limiting EPdensity gradient (critical gradient) is considered here. In this recipe, the critical gradient occurs when the AE linear growth rate, driven mainly by the EP gradient, exceeds the ion temperature gradient (ITG) or trapped electron mode (TEM) growth rate, driven by the thermal plasma gradient, at the same toroidal mode number (n) as the AE peak growth, well below the ITG/TEM peak n. This linear recipe for the critical gradient is validated against the critical gradient determined from far more expensive local nonlinear simulations in the gyrokinetic code GYRO, as identified by the point of transport runaway when all driving gradients are held fixed. The reduced linear model is extended to include the stabilization from equilibrium E×B velocity shear. The nonlinear verification unambiguously endorses one of two alternative recipes proposed in Ref. 1: the EPdriven AE growth rate should be determined with rather than without added thermal plasma drive.
 Authors:

^{[1]};
^{[2]}
 Univ. of California, San Diego, CA (United States)
 General Atomics, San Diego, CA (United States)
 Publication Date:
 Grant/Contract Number:
 FG0295ER54309; FC0208ER54977
 Type:
 Accepted Manuscript
 Journal Name:
 Physics of Plasmas
 Additional Journal Information:
 Journal Volume: 24; Journal Issue: 12; Journal ID: ISSN 1070664X
 Publisher:
 American Institute of Physics (AIP)
 Research Org:
 General Atomics, San Diego, CA (United States)
 Sponsoring Org:
 USDOE Office of Nuclear Energy (NE)
 Country of Publication:
 United States
 Language:
 English
 Subject:
 70 PLASMA PHYSICS AND FUSION TECHNOLOGY
 OSTI Identifier:
 1438438
 Alternate Identifier(s):
 OSTI ID: 1411993
Bass, Eric M., and Waltz, R. E.. Nonlinear verification of a linear critical gradient model for energetic particle transport by Alfven eigenmodes. United States: N. p.,
Web. doi:10.1063/1.4998420.
Bass, Eric M., & Waltz, R. E.. Nonlinear verification of a linear critical gradient model for energetic particle transport by Alfven eigenmodes. United States. doi:10.1063/1.4998420.
Bass, Eric M., and Waltz, R. E.. 2017.
"Nonlinear verification of a linear critical gradient model for energetic particle transport by Alfven eigenmodes". United States.
doi:10.1063/1.4998420. https://www.osti.gov/servlets/purl/1438438.
@article{osti_1438438,
title = {Nonlinear verification of a linear critical gradient model for energetic particle transport by Alfven eigenmodes},
author = {Bass, Eric M. and Waltz, R. E.},
abstractNote = {Here, a “stiff transport” critical gradient model of energetic particle (EP) transport by EPdriven Alfven eigenmodes (AEs) is verified against local nonlinear gyrokinetic simulations of a wellstudied beamheated DIIID discharge 146102. A greatly simplifying linear “recipe” for the limiting EPdensity gradient (critical gradient) is considered here. In this recipe, the critical gradient occurs when the AE linear growth rate, driven mainly by the EP gradient, exceeds the ion temperature gradient (ITG) or trapped electron mode (TEM) growth rate, driven by the thermal plasma gradient, at the same toroidal mode number (n) as the AE peak growth, well below the ITG/TEM peak n. This linear recipe for the critical gradient is validated against the critical gradient determined from far more expensive local nonlinear simulations in the gyrokinetic code GYRO, as identified by the point of transport runaway when all driving gradients are held fixed. The reduced linear model is extended to include the stabilization from equilibrium E×B velocity shear. The nonlinear verification unambiguously endorses one of two alternative recipes proposed in Ref. 1: the EPdriven AE growth rate should be determined with rather than without added thermal plasma drive.},
doi = {10.1063/1.4998420},
journal = {Physics of Plasmas},
number = 12,
volume = 24,
place = {United States},
year = {2017},
month = {12}
}