2019-10-10 -- CLau Poster

Numerical Model Developments for Turbulent Transport in C-2W
Calvin K. Lau1, Zhihong Lin2, Toshiki Tajima1,2, Sean Dettrick1, Lothar Schmitz1,3, and the TAE Team1
1 TAE Technologies, Inc., 19631 Pauling, Foothill Ranch, CA 92610 2 UNIVERSITY OF CALIFORNIA, IRVINE, Irvine, CA 92697 3UNIVERSITY OF CALIFORNIA, LOS ANGELES, Los Angeles, CA 90095
more questions? email me at clau@tae.com
APS-DPP 2019 / Ft. Lauderdale, Florida / October 21-25, 2019
n Full ion trajectories shown for ions
n SOL: can be described by guiding center
n Near separatrix: orbit width spans across separatrix, somewhat following field-line
n Core: orbit width spans across separatrix, does not necessarily follow field-line
n Largest fluctuations located in SOL despite inclusion of large orbit ionsàconsistent with past work
n Some differences in initial results:
n Faster time-scale observed: ~μs in growth-period
n Lower saturation level: ~O(10-2) eφ/Te
scrape-off layer (SOL)
separatrix
core
eφ/Te
Fig (ABOVE, LEFT): Electrostatic potential from simulation with drift-Lorentz deuterons. (LEFT) Outer dashed line is the separatrix, inner dashed line is the null point, at the midplane.
n Electrostatic particle-in-cell turbulence code (ANC)
n cross-separatrix simulations of multiple toroidal modes n gyrokinetic deuterons, adiabatic electrons
n Nonlinear simulations show inverse cascade in SOL [1]
n cascade due to mode-mode coupling from unstable shorter
to stable longer wavelength modes
n resulting SOL spectrum shape matches decreasing trend
measured in experiment
n Fluctuations spread from unstable SOL to stable core
n radial spreading via nonlocal gyroradius effects
n coreà no inherent instability found, fluctuations originate
from SOL leading to larger deviation in fluctuation level n resulting core spectrum magnitude matches experiment
Fig (ABOVE, RIGHT): Electrostatic potential from simulation at linear growing time (a,b) and after non-linear saturation (c,d).
n Some limitations of this work: n Gyrokinetic model
■ does not describe figure-8 or betatron orbits, only gyro-orbits
■ magnetic null regions not well described n Electrons adiabatic response model
■ particle flux not described
■ electron heat flux not self-consistently described
Motivation for model which
n avoids gyrokinetics
n large time-steps for low- frequency turbulence time-scales
Fig (ABOVE): Lines and shaded regions correspond to simulation results. Points are from experimental measurements via DBS.
n Newly implemented particle model blending full Lorentz and drift-kinetic orbits [2]
n Model used for ions and electrons, capable of capturing high and low frequency physics
Fig (ABOVE): benchmark of ion Bernstein wave dispersion in cylindrical geometry
Fig (ABOVE): benchmark of driftwave dispersion in cylindrical geometry
n Perturbative weight approach for higher signal-to-noise
n Local Maxwellian assumed for equilibrium f0
n Alternatively, can directly scatter (f - f0) during density calculation[3]
n Choose axial boundary at compilation: n Periodic or reflective
n For n=0, external potential can be set at axial boundaries to emulate electrode biasing: n due to perpendicular Laplacian, only affects simulation through electric fields near ends
n Equilibrium electric field can also be set based on initial conditions: n affects simulations through E0 x B0 velocity on particle motion
n To remove high frequency oscillations beyond low-frequency turbulence,
cut-off parallel velocity set for electrons[4]:
n faster than cut-off velocity: assumed adiabatic response on LHS
n slower than cut-off velocity: modeled with simulation markers, perturbed electron
density on RHS
ion polarization density
non-adiabatic electron perturbed density
electron polarization density
electron adiabatic response
AC K N O W L E D G E M E N T S
Simulations used the resources of DOE Office of Science User Facilities: National Energy
Research Scientific Computing Center (DOE Contract No. DE-AC02-05CH11231) and Innovative and Novel Computational Impact on Theory and Experiment (INCITE) program at Argonne Leadership Computing Facility at Argonne National Laboratory (DOE Contract No. DE-AC02-06CH11357).
References
[1] CK Lau et al, Nucl. Fusion (2019)
[2] RH Cohen et al, Nucl. Inst. & Methods Phys. Res. (2007) [3] SJ Allfrey and R Hatzky, Comp. Phys. Comm. (2003)
[4] AM Dimits and WW Lee, J. Comp. Phys. (1993)
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