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SUMMARY:Global gyrokinetic simulations of TAEs in ITER and ASDEX Upgrade
DTSTART;VALUE=DATE-TIME:20210511T101000Z
DTEND;VALUE=DATE-TIME:20210511T103000Z
DTSTAMP;VALUE=DATE-TIME:20210417T022609Z
UID:indico-contribution-17183@conferences.iaea.org
DESCRIPTION:Speakers: Thomas Hayward-Schneider (Max Planck Institute for P
lasma Physics)\nThis work reports on a breakthrough on the way to a compre
hensive modelling of burning fusion plasmas. For the first time\, global e
lectromagnetic gyrokinetic PIC simulations of Alfvénic modes have been su
ccessfully performed for a high beta ITER plasma.\nThis finally gives us t
he ability to model alpha particle driven modes self-consistently in the n
on-linear regime and to predict the related alpha particle transport with
a high level of confidence.\nThe ITER 15 MA scenario [1]\, with significan
t alpha particle pressure\, is a scenario in which a broad range of Alfvé
n eigenmodes may be present. More specifically\, a large number of possibl
e of toroidal Alfvén eigenmodes (TAEs) can exist in the plasma\, and mult
iple of these may be driven by the alpha particle gradient. Whilst the ind
uced transport is expected to be small at nominal parameters\, it is of si
gnificant interest to consider the sensitivity and borders to enhanced tra
nsport regimes. Previous modelling of this discharge has been performed (s
ee\, for example reference [2] and references therein)\, most notably by p
erturbative hybrid (MHD or gyrokinetic eigenvalues and drift- or gyro-kine
tic energetic particles)\, nonperturbative hybrid MHD-kinetic\, or local g
yrokinetic. Although we know that kinetic\, nonperturbative\, and global e
ffects are important for the TAEs in ITER\, due largely to the difficultie
s caused by the large size and high plasma β of ITER\, it has previously
not been possible to apply nonlinear models containing all of these effect
s consistently. In parallel to this\, significant progress [3] has recentl
y been made in global\, electromagnetic gyrokinetics\, which has yielded e
.g. detailed nonlinear studies of energetic particle driven Alfvén eigenm
odes in simplified conditions [4]\; benchmarks of Alfvén eigenmodes in ex
perimental conditions [5\, 6]\; and the nonlinear interaction between elec
tromagnetic turbulence and Alfvén modes [7].\nThe simulations in this wor
k are performed with the ORB5 code [8\, 9]\, a global electromagnetic part
icle-in-cell (PIC) code using spectrally filtered finite elements for the
representation of the fields\, with all species considered kinetically\, a
nd using the “pullback scheme” [3] to mitigate the cancellation proble
m.\n\nIn this contribution\, we present the first application of a global
nonlinear electromagnetic gyrokinetic code to address the issue of TAE sta
bility in ITER\, focussing first on the linear stability of the modes over
a range of mode numbers and gap positions\, before looking at the saturat
ion observed when retaining the wave-particle nonlinearity. This is expand
ed by considering also multiple modes present simultaneously\, observing a
significant increase of the mode saturation levels by approximately one o
rder of magnitude\, and accordingly increased alpha particle redistributio
n\, in a case with double the nominal alpha particle density\, and when ne
glecting the gyro-average on the energetic particles. This is consistent w
ith the finding of previous hybrid modelling [10].\n\nIn the linear regime
\, we observe a range of mode numbers for which there exist multiple eigen
modes\, with global mode structures spanning multiple gaps\, reflecting wh
at is found with linear eigenvalue calculations. We show that these cases
require a global domain to describe the linear mode properties. For more l
ocalized mode structures\, with higher mode numbers\, considering a reduce
d domain is justified\, and we see close agreement\, even for nonlinear sa
turation levels between full and reduced radial domains.\n\n![Snapshot of
global n=12 TAE mode structure][21]\nFigure 1: A snapshot of the absolute
magnitude of the poloidal harmonics of the electrostatic potential of an n
=12 TAE in the linear phase.\n\nIn linear simulations without energetic pa
rticles present\, where we allow an initial perturbation to decay until ei
genmodes are observed\, we find also different modes present\, for example
those from the higher frequency gaps (e.g. EAE and NAE)\, as well as odd-
parity TAEs from the upper part of the gap\, as these modes (although bare
ly driven in the presence of energetic particles) are weakly damped. An in
teresting observation is that in the post-saturation phase of the nonlinea
r multi-mode TAE simulations\, we also observe odd-parity TAEs present. Th
is observation motivates a reconsideration of which modes to include for h
ybrid perturbative simulations of the same scenario\, where previously the
odd-parity modes were neglected a priori due to the weak drive.\n\n![Nonl
inear saturation of TAEs with toroidal mode numbers 20-30][22]\nFigure 2:
Time evolution of the peak radial values of the different toroidal mode nu
mbers of the electrostatic potential in a nonlinear simulation.\n\n\nTo ma
ke simulations feasible\, we have allowed several simplifications of the p
hysics problem\, but we have considered the impact of each\, which we will
discuss\, in particular\, we show the effect of reducing the ion/electron
mass ratio.\n\nWe also present the application of the ORB5 code to an exp
erimental case taken from an ASDEX Upgrade discharge with particularly int
eresting energetic particle physics [11]\, and this result is benchmarked
against hybrid codes. The details of this benchmark will be presented in r
eference [12].\n\n\n\n\nAcknowledgement: This work has been carried out wi
thin the framework of the EUROfusion\nConsortium and has received funding
from the Euratom research and training programme 2014-\n2018 and 2019-2020
under grant agreement No 633053. The views and opinions expressed herein\
ndo not necessarily reflect those of the European Commission.\n\n\nReferen
ces\n[1] A. Polevoi et al.\, JPFR-S\, (2002)\n[2] S. Pinches et al.\, Phys
. Plasmas (2015)\n[3] A. Mishchenko et al.\, Comp. Phys. Comm. (2019)\n[4]
M. Cole et al.\, Phys. Plasmas (2017)\n[5] S. Taimourzadeh et al.\, Nucle
ar Fusion (2019)\n[6] F. Vannini et al.\, Submitted to Physics of Plasmas\
n[7] A. Biancalani et al.\, this meeting\n[8] S. Jolliet et al.\, Comp. Ph
ys. Comm. (2007)\n[9] E. Lanti et al.\, Comp. Phys. Comm. (2020)\n[10] M.
Schneller et al.\, Plasma Phys. Control. Fusion (2015)\n[11] Ph. Lauber et
al\, EX1/1 Proc. 27th IAEA FEC (2018)\n[12] G. Vlad et al\, this meeting\
n\n\n [21]: https://datashare.mpcdf.mpg.de/s/5Wxw3lERUqbUX2z/download\n
[22]: https://datashare.mpcdf.mpg.de/s/t558WiVjMuJrpJn/download\n\nhttps:/
/conferences.iaea.org/event/214/contributions/17183/
LOCATION:Virtual Event
URL:https://conferences.iaea.org/event/214/contributions/17183/
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