23F01
Effects of Magnetic Nozzle Configuration on an Applied Field MPD Arcjet
MPD
Naohiro Takahashi, Yuko Hashima, Kohei Okawa, Hiroshi Watanabe, Yuki Izawa,Nozomi Tanaka and Akira Ando,,,,Graduate School of Engineering, Tohoku University
6-6-05, Aoba, Aramaki, Aoba-ku, Sendai, 980-0879, Japan
980-8579
6-6-05A Magneto-Plasma-Dynamic arcjet (MPDA) is one of the promising candidates for high power thrusterwith electric propulsion system. In order to investigate the effect of applied field on a MPDA, we haveinvestigated plume plasma parameters and thrust performance in an applied field MPDA. Different types ofdivergent magnetic field were applied to a MPDA, and thrust was measured using a pendulum type target.
Thrust increased with a discharge current and applied magnetic field. Maximum thrust was obtained when
the peak position of applied magnetic field is set at upstream of the MPDA.

1. Introduction
A high-power thruster with higher specificimpulse and larger thrust is requisite for mannedinterplanetary space missions. An electric
propulsion system is suitable for long-term missionin space with its higher specific impulse.
Magneto-Plasma-Dynamic arcjet (MPDA) is one ofthe promising candidates for the high powerthruster utilizing electric propulsion system. It has
been reported that the propulsion performance of a
MPDA improves by applying a magnetic field on it[1-3].
When an axial magnetic field is applied on aMPDA, an azimuthal acceleration force appears androtates the plasma, resulting in an axial acceleration
with swirl acceleration. Hall acceleration is also
expected by an azimuthal Hall current and radial
magnetic field [4]. The azimuthal plasma rotation
eliminates current concentration on the electrodes
and reduces electrode erosion.
We have conducted experiments of plasma
acceleration by applying a divergent magnetic field
to a MPDA. When exhausted plasma passed
through the divergent field, plasma was accelerated
and its Mach number increased. A supersonic andsuper-Alfvénic plasma was formed in thedownstream region of the divergent magnetic field[5-7]. With a divergent magnetic field on a MPDA,
electron density and temperature increased.
The thrust force of the applied field MPDA wasestimated by measuring the plasma parameters of
the flow [8]. We have measured the velocity,
density, temperature and spatial profiles of theplasma flow, and calculated thrust from total
momentum of the plume plasma.
In order to evaluate the thrust generated in theapplied field MPDA, a pendulum type target wasfabricated and the thrust was measured. In thispaper, we report the effect of applied field on thethrust performance. The intensity and the positionof applied magnetic field configuration werechanged and its effect on the thrust wasinvestigated.
2. Experimental setup
Experiments were performed in the HITOP
device in Tohoku University. The HITOP device
consists of a large cylindrical vacuum chamber(diameter D = 0.8 m, Length L = 3.4 m) andexternal magnetic coils, which can generate a
uniform magnetic field up to 0.1 T. A high-power,
quasi-steady MPDA is installed at one end of theHITOP device. It has a coaxial structure with acenter tungsten cathode rod (10 mm outer diameter)
and an annular molybdenum anode (30 mm innerdiameter). A quasi-steady discharge continues for 1
msec with a pulse-forming-network (PFN). A fast
acting gas valve puffs working gas into thedischarge region with the duration of about 3ms.
Maximum value of discharge current Id is 10 kA
and a typical discharge voltage Vd is 100 - 200 V
depending on the applied field intensity. The
MPDA has a small magnetic coil outside of theelectrodes and it can apply a strong magnetic field
up to 0.5 T.
In this study, the impulse bit (=F∆t, where F isthrust and ∆t is pulse duration of the discharge) wasmeasured by using a pendulum type cylindricaltarget [9]. The main part of the target was a numberof plate disks with a center hole and a bottom cone
made of stainless steel (see Fig.1). Plasma plumecomes into the cylindrical target through the frontSupporting point

Cylindrical Target

0.3
(a)
(b)
(c)

0.25

B0(T)

plate with an entrance hole of 100 mm in diameter.
In order to eliminate the effect of particle reflection
on the thrust measurement, a number of disk plates
formed a many slits around the target. Most of thegas particles reflected from the bottom plate are
expected to escape radially from the side slits.
When the pulsed plasma flow comes in, the target
starts to swing. The swing amplitude depends on
the impulse bit. The calibration between the swing
amplitude and the impulse bit was performed before
the experiment.

0.2

0.15

Aditional
magnetic field (Bzp)

0.1

0.05
Uniform magnetic field (B0)

0-0.1

0Z(m)

0.1

0.2

Fig.2. Three types of the magnetic configurations near
the MPDA. The peak positions are set at (a)upstream of MPDA, (b) the top of cathode and (c)downstream of MPDA.

MPDATovacuum chamber
Opticaldisplacement meterFig.1. Experimental setup.

3. Experimental results
Various types of applied magnetic field
configuration were examined as shown in Fig. 2.
Both of a uniform magnetic field (B0) and an
additional magnetic field (Bzp) by the small coilattached on the MPDA formed a divergent orconvergent-divergent magnetic configuration at theMPDA exit. The peak positions of each magnetic
field were set at (a) upstream of MPDA, (b) tip ofthe cathode and (c) downstream of MPDA.
Figure 3 shows the dependence of thrustmeasured by the thrust target on the discharge
current with the magnetic field of B0=50 mT and
Bzp=0.14 T. The working gas was He with mass
flow rate of 0.062 g/sec. The thrust increased withthe discharge current in each configurations. Larger
thrust was obtained when the peak position was set
at upstream of the MPDA. We have measured thedependences on the discharge current, magnetic
field strength and gas species. The thrust increasedwith larger magnetic field strength. The thrust andplasma parameters with these three divergent fields
were measured and the results will be presented.
References[1] H. Tahara, F. Takiguchi, Y. Kagaya and T. Yoshikawa:
22nd Int. Electric Propulsion Conf., IEPC-91-073.

Thrust(N)

5(a)

4(b)

3(c)

210He
B =50mT+B =0.14T
zp

00

1

2

34

5

67I (kA)dFig.3. The dependence of thrust on the discharge current
with the three types of the magnetic field
configurations as shown in Fig.2. B0=50 mT and
Bzp=0.14 T.
(1991).
[2] A. Sasoh: Journal of Propulsion and Power, 10(1994) 251.
[3] D. B. Fradkin, A. W. Blackstock, D. J. Roehling, K.
W. Liewer, T. F. Stratton, and M. Williams: AIAA
Journal, 8 (1970) 886.
[4] H. Tobari, A. Ando, M. Inutake, and K. Hattori:
Physics of Plasmas, 14 (2007) 093507.
[5] M. Inutake, A. Ando, K. Hattori, H. Tobari, and T.
Yanagi: Journal of Plasma Fusion Research, 78(2002) 1352.
[6] S. Jo, R. Aramaki, T. Taguchi, A. Komuro, and A.
Ando: Space Transport Symposium 2009,
STEP-2008-22 (2009).
[7] R. Aramaki, S. Jo, N. Takahashi, and A. Ando: Proc.
APFA2009, P27p2-43 (2009) p.103.
[8] N. Takahashi, R. Aramaki, Y. Hashima, Y. maruko, N.
Tanaka, and A. Ando: Space Transport Symposium
2011, STEP-2010-042 (2011).
[9] R. Yanagi and I. Kimura: Journal of Spacecraft andRocket, 19 (1982) 246.