7th Asia-Pacific Conference on Plasma Physics, 12-17 Nov, 2023 at Port Messe Nagoya

Molecular dynamics simulations of interactions with various materials startingwith plasma-wall interaction studies

Hiroaki Nakamura1,2, Seiki Saito3, Keiji Sawada4, Masahiro Hasuo5,
Masahiro Kobayashi1, Yuji Hatano6, Susumu Fujiwara7
1
National Institute for Fusion Science, 2 Grad. School of Engineering, Nagoya University, 3 Grad.
School of Science and Engineering, Yamagata University, 4 Faculty of Engineering, Shinshu
University, 5 Grad. School of Engineering, Kyoto University, 6 Hydrogen Isotope Research Center,Toyama University, 7 Faculty of Materials Science and Engineering, Kyoto Institute of Technology
e-mail (speaker): hnakamura@nifs.ac.jp
1. Plasma-wall interaction
In a fusion plasma device, itis necessary to confine
high-temperature plasma in avacuum vessel. In thisprocess, the plasma isdesigned to come into contact
a component called thedivertor
plate,
which
minimizes dissolution heatingof the vessel. We used
Figure 1 Hydrogenmolecular dynamics (MD)molecule fromsimulation to study plasma
graphite wall[3].
irradiation-induced damage todivertor plates (see Figure 1). Here, the plasma-wallinteraction (PWI) is calculated by MD for elementary
processes. This simulation was our first application of
the MD method to fusion research[1-6].
2. DNA double-strand breakIn recent years, starting withthis PWI research, we have
expanded the scope of
application beyond divertor
plates. In the MD method, themotion trajectory of many
particles can be obtained bynumerically integrating theFigure 2 Snapshot ofclassical equation of motion.
DNA double-strand
Taking advantage of thisbreaks
feature, we quantitativelyevaluated the effects of tritium on biomolecules (DNA).
Tritium, a radioactive isotope of hydrogen, which is thefuel of the nuclear fusion reactor, emits β-rays. External
exposure is not a problem, only internal exposure caused
by taking tritium into the body needs to be controlled.
In order for fusion power generation to be accepted bysociety, it is necessary to accumulate scientificknowledge that will enable a rigorous assessment of therisks of tritium[7,8]. Therefore, we evaluatedtritium-induced DNA damage by MD[9] as shown in
Figure 2.
3. Chiral nanoneedle by optical vortex
The third topic is electromagnetic fields, which areoften used to heat fusion plasmas. As thiselectromagnetic field, we consider an optical vortex,
which is an electromagnetic wave with orbital angularmomentum. It is known thatwhen a metal is irradiatedwith an optical vortex, thesurface of the material melts
intoa
helicalnanostructure[10], and wehave successfully createdthis structure on a computer
using MD (Figure 3). We
introduce this structure
Figure 3 Structureformation obtained by MD
formation of chiralsimulation[11].
nanoneedle[11]Acknowledgments
The research was supported by Japan Society for thePromotion of Science (Grant Nos.JP22H05131,JP23H04609, JP23K03362), by the NIFS Collaborative
Research Programs (NIFS22KIIP003, NIFS22KIGS002,NIFS22KISS021) and by the ExCELLS Special
Collaboration Program of Exploratory Research Center
on Life and Living Systems. The computation wasperformed using Research Center for Computational
Science, Okazaki, Japan (Project: 22-IMS-C104) andPlasma Simulator of NIFS.
References[1] K. Sawada and M. Goto, Atoms 4 (2016), 29.
[2] S. Saito et al., Contributions to Plasma Physics, 60(2020) e201900152.
[3] H. Nakamura et al., Jpn. J. Appl. Phys. 61 (2022)
SA1005.
[4] K. Sawada et al., Contrib. to Plasma Phys. 60 (2020)
e201900153.
[5] S. Saito et al., Jpn. J. Appl. Phys. 60(2020)SAAB08.
[6] H. Nakamura et al., J. Adv. Simulat. Sci. Eng.
10(2023)132.
[7] Y. Hatano et al., J. Adv. Simulat. Sci. Eng.
9(2022)198.
[8] Y. Hatano et al., Enzymes 51(2022) 131. DOI:
10.1016/bs.enz.2022.08.009[9] H. Nakamura et al., Jpn. J. Appl. Phys.
61(2022)SA1005.
[10] K. Toyoda et al., Phys. Rev. Lett., 110(2013)
143603.
[11] H. Nakamura and S. Habu, Jpn. J. Appl. Phys.
62(2022)SA101