28D03P
開放端磁場で膨張加速する希薄弱電離アークジェットのDSMCシミュレーション
DSMC Simulation of Flowing Characteristics of Rarefied Weakly-Ionized
Arc-Jet Expanding along Open-Field-Line中萩健志1), 根津 篤2), 3), 松浦治明3), 赤塚 洋1), 3)
Takeshi Nakahagi, Atsushi Nezu, Haruaki Matsuura and Hiroshi Akatsuka
1)東工大・院総理工, 2)東工大・技術部, 3)東工大・原子炉研Tokyo Institute of Technology
We have been studying fluid dynamic
characteristics of arc-jet helium plasma flowing alongopen-field-line experimentally [1 – 3]. However, it isstill difficult for us to understand the rigorous physicsof acceleration/deceleration of ions in the plasma flow
as well as variation in space potential. We should carryout numerical simulation by modeling the plasma flow
to understand the plasma flow entirely. The objectiveof the present study is to understand the plasma flow at
the open-magnetic field by numerical simulation.
The plasma has low ionization degree, whichindicates that we must solve the flow of neutral
particles simultaneously. We must also treat the ion
flow as a rarefied dynamic flow since the Knudsen
number of the ion flow Kn is larger than about 0.15.
Consequently, we applied the Direct Simulation Monte
Carlo (DSMC) method to solve the Boltzmann
equation stochastically. We solve the problem as anaxi-symmetric problem, where particle movement istreated as 3-D while the collision as 2-D [4, 5]. To
overcome the statistical fluctuation of ions as minor
species, we applied weighting factor method andsolved the neutral particles simultaneously [4].
Although we should solve electrons simultaneously,
we supposed that the electron density, velocity andtemperature are the same with those of ions,
respectively, for simple analysis. We also assumed thatthe space potential was already given as the values
observed experimentally [1– 3]. We applied maximum
collision number method to simulate collisions, where
we considered elastic and charge-transfer collisions
between an ion and a neutral particle, and elastic
collisions between neutral particles [4, 5].
Figures 1(a) – 1(c) show dependence of number
density, Mach number and temperature of both ionsand neutral particles, respectively, calculated for theon-axis r = 0. It was found that the larger ionization
degree results in the larger maximum Mach number inthe vicinity of diverging magnetic field, and that it
causes the further extension of the acceleration domain.
It was also found that the lower ionization degree
makes the maximum ion temperature higher. We foundthat the numerical results of Mach number andtemperature qualitatively agree with our previous
experimental results, where the best agreement was forthe assumption of ionization degree 10–2.

Fig. 1. Numerical results calculated for on-axis(r =0) condition; (a) number density, (b)Machnumber and (c) temperature. Weighting factor is
the reciprocal ionization degree, which were set
to be 10, 100 and 1000.
[1] K. Yoshida, T. Kanuma, H. Ichii, A. Nezu, H. Matsuura
and H. Akatsuka, IEEJ Trans., 4, 416 – 421 (2009).
[2] K. Yoshida, T. Shibata, A. Nezu, H. Matsuura and H.
Akatsuka, J. Plasma Fusion Res. Series, 8, 923 – 927 (2009).
[3] K. Yoshida, T. Shibata, A. Nezu, H. Matsuura and H.
Akatsuka, IEEE Trans. Plasma Sci., 37, 1414 – 1418 (2009).
[4] T. Ichiki, T. Sakamoto, H. Matsuura and H. Akatsuka, J.
Plasma Fusion Res. Series, 8, 768 – 772 (2009).
[5] H. Akatsuka, A. N. Ezoubtchenko and M. Suzuki, J.
Phys. D: Appl. Phys., 33, 948 – 959 (2000).