Speaker
Shimpei Futatani
Description
See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P5.1036.pdf
Non-linear MHD simulations of the plasma instabilities
by pellet injection in LHD plasma
Shimpei Futatani1 and Yasuhiro Suzuki2,3
1
Department of Physics, Universitat Politècnica de Catalunya (UPC), Barcelona, Spain
2
National Institute for Fusion Science (NIFS), 322-6 Oroshi-cho, Toki 509-5292, Japan
3
Tha Graduate University for Advanced Studies (SOKENDAI), 322-6 Oroshi-cho, Toki 509-5292,
Japan
The pellet injection is an experimentally proven method of plasma refueling in tokamaks
[1,2] and stellarators plasmas [3]. The pellet injection into the plasma is also used for plasma
control, i.e. ELM (Edge Localized Mode) mitigation for tokamaks by means of the excitation
of the Magnetohydrodynamic (MHD) activities via pellet injection. However, the plasma
instabilities which are inimical phenomena via pellet injection are problems that have come
into focus simultaneously. It is crucial to identify the complex physics mechanism between
the plasma stability and the pellet ablation physics with non-linear MHD analysis.
In this work, the global MHD dynamics of the Large Helical Device (LHD), which is a large
superconducting Heliotron in Japan, has been analyzed with MIPS code [4] which solves the
full MHD equations coupled with the pellet ablation model. The pellet ablation model which
is based on neutral gas shielding model has been implemented in MIPS. The two important
features are reflected in the implementation of the model into MIPS code in a similar manner
with JOREK [5,6]. The first feature is that the pellet is modelled as a localized adiabatic
time-varying density source. The pellet density source is toroidally and poloidally localized.
The second feature is that the pellet moves at fixed speed and the direction.
Initial MIPS-Pellet runs for non-linear MHD dynamics have been performed. The modelled
LHD plasma has the edge electron pressure (p e) of 1 kPa and pe of the core region is 7.8 kPa.
The electron temperature (Te) at the edge is 0.4 keV and the core is 2.1 keV. The results of the
pellet size dependence in the LHD plasmas show that the pellet penetration depth ranges for
0.5-0.7 m according to the pellet size which is scanned for 1.0x10 21D, 1.5x1021D and
2.0x10 21D particles in a pellet. The simulation result is reasonably comparable values with
the experiment observation [7]. The transport of the pellet cloud in the whole plasma domain
in a time scale of the pellet ablation which is typically 400-600s has been observed.
The performance of the parallel computing has been analyzed using MareNostrum IV which
is the most powerful supercomputer in Barcelona, Spain. The numerical resolution of the
simulation domain for the test case is 128x128x256. The number of cores has been varied for
16, 32, 64, 128, 256, 512, 1024, 2048, 4096, 8192, 16384 cores. The speed of the MPI
computing increases linearly according to the number of cores until 4096 cores. A detailed
analysis and an optimization will be carried out as a future work.
References:
[1] L. Baylor et al., Physi. Plasmas 12, 056103 (2005). [2] P.T. Lang et al., Nucl. Fusion 41
1107 (2001). [3] R. Sakamoto et al., Nucl. Fusion 44, 624 (2004). [4] K. Ichiguchi et al.,
Nucl. Fusion 55, 073023 (2015). [5] G.T.A. Huysmans and O. Czarny, Nucl. Fusion 47, 659
(2007). [6] S. Futatani et al., Nucl. Fusion 54, 073008 (2014). [7] T. Bando et al., Physics of
Plasmas 25, 012507 (2018).
