A. Ando

H. Miyazaki

H. Tobari

K. Hattori

K. Yoshino

M. Inutake

National Institute for Fusion Science (NIFS-Repository)

§8. Measurement and Control of a High-Mach-Number Plasma Flow Inutake, M., Ando, A., Hattori, K., Miyazaki, H., Yoshino, K., Tobari, H. (Dept. of Electrical Engineering, Tohoku Univ.) Production of a high-beta, supersonic plasma flow with a magnetic field is quite important for basic researches on MHD phenomena in space and fusion plasmas. A magneto-plasma-dynamic arc-jet (MPDA) is one of the promising devices to produce a supersonic plasma flow and is utilized as an electric propulsion with a higher specific im-pulse and larger thrust. Plasma flow velocity of the MPDA is expected to increase by applying an external divergent magnetic nozzle which converts a high ion ther-mal energy to an axial flow energy. In a diver-gent magnetic nozzle configuration, a supersonic plasma flow with ion acoustic Mach number, M i , up to 3 has been successfully obtained in the far downstream region of the MPDA. In a uniform axial magnetic field configuration, on the other hand, the Mach number is limited at the value near unity [1]. From spectroscopic measurements in the vicinity of the MPDA muzzle it is found that both axial and rotational flow velocities in-crease linearly with the increase of discharge cur-rent, but, at the same time, ion temperature in-creases more steeply, resulting in the limitation of Mi less than unity in the vicinity of the muzzle [2]. To realize a supersonic plasma flow with more higher M i , it is very important to develop an opti-mum magnetic nozzle configuration in the vicinity of the MPDA muzzle. A small-sized coil with a stronger field is attached near the MPDA muz-zle to form a Laval-type magnetic nozzle config-uration. The subsonic flow near the muzzle is expected to be supersonic through the magnetic Laval nozzle, as is in a conventional compress-ible gas flow. As shown in Fig.I, it is found that the ion Mach number increases from 1 to 1.5 by the addition of the small magnetic Laval nozzle. With the nozzle magnetic field attached, the ra-tio, JII / J l.., which is proportional to M i , increases at a higher discharge current Id , though without the attached nozzle field it tends to saturate as shown in Fig.2. (a) B-field -Bo(O.065T) +Bn(O.3T) 0.4 ••••• B o(o.065T) E 0.3 Mach probe 0.2 . Z=128cm t In 0.1 0 0 0.5 Z(m) 1.5 Ci' 3 (b) Nozzle coil current 0.4 ~ 2 0.3 E _z 1 0.2 rtJz 0.1 0 0 120 -N E 80 u ~ 40 • ...,-0 2 4 -i ..., 1 ~-::::: 2 ..., 0 0 0 0.5 1 1.5 2 time (ms) Fig. 1. Axial profiles of (a) Bo and BN, (b) IN, (c) JII and J1. and (d)Mi. Id = 8.2kA. 5~~--~~--~~ 4 ...,-i 3 . 0 ~ 2 r'-'--~-'i ..., 1 • BH=3kGI .' . ~ . ~. ~ 00 0) 1 ·1 0 BH=OkG 1 . ~L=~~~~ __ ~~ o Q ,.... Ne 40 u ~ -:::::20 ..., ~ 15 u ~ 10 :;-i 5 00 2 4 6 8 10 I d (kA) Fig. 2. (a) JII / J1. , (b) JII' (c) J1. as a function of Id. References 1) Inutake, M. et.al.: Proc. of 10th ICPP2000 (Que-bec) 1, (2000) 148. 2) Ando, A. et.al.: J. Plasma Fusion Res. SERIES, 4, (2001) 373. 311 

Measurement and Control of a High-Mach-Number Plasma Flow

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