57th Annual Meeting of the APS Division of Plasma Physics
Volume 60, Number 19
Monday–Friday, November 16–20, 2015;
Savannah, Georgia
Session BI2: Pedestals
9:30 AM–12:30 PM,
Monday, November 16, 2015
Room: Chatham Ballroom C
Chair: Masayuki Ono, Princeton Plasma Physics Laboratory
Abstract ID: BAPS.2015.DPP.BI2.2
Abstract: BI2.00002 : Toward integrated multi-scale simulations for a full ELM cycle with ELM dynamics*
10:00 AM–10:30 AM
Preview Abstract
Abstract
Author:
Xueqiao Xu
(Lawrence Livermore National Laboratory)
The high-fidelity BOUT$++$ two-fluid and Gyro-Landau-Fluid code suites have
demonstrated significant recent progresses toward integrated multi-scale
simulations for a full ELM cycle with ELM dynamics. In order to improve the
computational efficiency for a full ELM cycle with ELM dynamics, the basic
set of dynamical equations has been separated into equations in the
fluctuating and averaged parts over binormal direction. The two parts are
advanced together in time but with different time steps, and dynamically
exchange the turbulence fluxes and averaged profiles. Nonlinear ELM
simulations show three stages of an ELM event: (1) a linear growing phase;
(2) a fast crash phase; and (3) a slow inward propagation phase lasting
until the core heating flux balances the ELM energy loss and the ELM is
terminated. To better understand the inter-ELM pedestal dynamics during the
pedestal recovery, BOUT$++$ simulations started from a kinetic equilibrium
reconstruction using measured plasma profiles from DIII-D show that
quasi-coherent fluctuations (QCFs) can provide the necessary transport to
limit and saturate the H-mode pedestal gradient. The simulations predict
that (1) QCFs are localized in the pedestal region as observed on DIII-D;
(2) the QCFs are near marginal instability for ideal ballooning modes
combined with drift-Alfven wave modes; (3) the dominant mode is around
n$=$15, k$_{\mathrm{\theta }}\rho_{\mathrm{i}}=$0.034, comparable to
the measured value of 0.04; (4) the frequency of the mode is around 80kHz,
close to that of the measured QCF; and (5) particle transport is smaller
than the heat transport. BOUT$++$ simulations have also been performed to
elucidate the nature and underlying physics mechanisms of the
weakly-quasi-coherent mode (WCM) with higher collisionality, which causes
particle transport in I-mode pedestals of Alcator C-Mod. Key simulation
results are that (1) there is no ideal peeling-ballooning mode instability
for the I-mode studied; (2) a strong instability exists at n $\ge $ 20; (3)
the mode propagates in the electron diamagnetic direction; (4) the predicted
frequency of the n$=$20 mode agrees with the measured WCM peaking around
300kHz; (5) the predicted $\chi_{\mathrm{e}}$ agrees with the $\chi
_{\mathrm{eff}}$ from the experiment; and (6) the predicted
particle transport is larger than the predicted heat transport.
*USDOE by LLNL under Contract DE-AC52-07NA2734. LLNL-ABS-674450
To cite this abstract, use the following reference: http://meetings.aps.org/link/BAPS.2015.DPP.BI2.2