Speaker
Description
The TGLF-EP [1] and Alpha [2] codes for the critical-gradient model (CGM) of energetic-particle (EP) transport have been unified and verified by nonlinear gyrokinetic simulations and validated against five DIII-D H-mode scenarios for ITER. This reduced model predicts the degree to which Alfvén eigenmodes (AEs) destabilized by EPs—in this case fast ions from neutral beam injection—radially flatten the classical slowing-down EP profile. It finds the steady-state solution of a local 1D radial transport equation under a stiff critical gradient approximation for AE transport with an estimated (small) contribution from microturbulence [3] and including the physical source and sink profiles. While such a reduced CGM neglects phase-space dynamics, finite orbit effects [4], and nonlinear effects such as transport intermittency and frequency chirping, kinetic simulations [5,6] combined with experimental evidence for EP profile resiliency [7] strongly suggest AE-EP transport is clamped to a critical gradient. Our validation study confirms broad applicability of the unified TGLF-EP+Alpha code in predicting the time-averaged density profile in DIII-D. The critical gradient, the model’s key input, comes from linear solutions of the TGLF [8] gyro-Landau fluid code, optimized for EP-AE physics, automated, and highly parallelized by the TGLF-EP wrapper code. TGLF-EP+Alpha, under development by the SciDAC ISEP center as an EP module for the future fusion whole-device-modeling project, is fully physics based, requiring only the equilibrium and beam source as inputs. It is computationally inexpensive enough (<30 minutes turnaround time versus over one month for first-principles models) to perform scoping studies needed for scenario optimization. DIII-D cases considered represent a wide range of EP transport, with observed neutron production near classical predictions down to an 80% deficit. TRANSP simulations using the EP diffusion coefficient predicted by TGLF-EP+Alpha find neutron deficits within 20% of experimental observations in applicable cases. Predicted AEs are consistent with previous studies [9].
Work supported by U.S. Department of Energy under Grants DE-FG02-95ER54309 (theory), DE-SC0018108 (SciDAC-ISEP project), and DE-FC02-04ER54698 (DIII-D).
[1] He Sheng, R.E. Waltz, and G.M. Staebler, Phys. Plasmas 24, 072305 (2017)
[2] R.E. Waltz and E.M. Bass, Nucl. Fusion 54, 104006 (2014)
[3] C. Angioni, A.G. Peters, G.V. Pereverzev, A. Botino, J. Candy, et al, Nucl. Fusion
49, 055013
(2009)
[4] X. Chen, M. E. Austin, R. K. Fisher, W. W. Heidbrink, G. J. Kramer, et al, Phys. Rev. Lett. 110, 065004 (2013)
[5] E. M. Bass and R. E. Waltz, Phys. Plasmas 17, 112319 (2010)
[6] Y. Todo, New J. Phys. 18, 115005 (2016)
[7] W. W. Heidbrink, W. W. Heidbrink, M. A. Van Zeeland, M. E. Austin, E. M. Bass, K. Ghantous, et al, Nucl. Fusion 53, 093006 (2013)
[8] G. M. Staebler, J. E. Kinsey, and R. E. Waltz, Phys. Plasmas 14, 55909 (2007)
[9] Zhen-Zhen Ren, G. Y. Fu, M. A. Van Zeeland, Feng Wang, Zheng-Xiong Wang, et al, Phys. Plasmas 25, 122504 (2018)
| Country or International Organization | United States |
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