S-B2-3
Plasma Acceleration using Electromagnetic Waves and Tasks forHigh Power Electric Propulsion
高周波を用いた加速技術と大電力電気推進技術への課題
Akira Ando,
安藤 晃
Graduate School of Engineering, Tohoku University
6-6-05, Aoba-yama, Sendai 980-8579, Japan東北大学大学院工学研究科 〒980-8579 仙台市青葉区荒巻字青葉6-6-05
For the future electric propulsion (EP) systems, high power thruster utilizing plasma production andacceleration with no electrode is inevitable. A number of researches have started to develop EP systems
using electromagnetic (EM) waves in plasma production and acceleration. An ion acceleration by thecombination of ion cyclotron heating and magnetic nozzle was successfully demonstrated in the HITOP
and VX-devices. Direct formation of acceleration potential without electrode has performed in a double
layer thruster. A rotating elelctromagnetic field is used to accelerate plasma by Lorentz force withexpanding magnetic field. Development of reliable and efficient power sources and formation of magnetic
field are important for the utilization of EM waves in high power thrusters.

1. Introduction
An electric propulsion (EP) system is one of
the key elements in future space exploration
projects and has been developed for various space
missions [1]. The exhaust ion velocity of EP is10-100 times as fast as that of chemical rockets.
This feature of EP makes possible long-term
space missions with less consumption ofpropellant.
Recent remarkable achievement of thespacecraft HAYABUSA encourages further
development and utilization of EP system not
only for an orbital station-keeping rocket but for amain engine of spacecrafts [2,3].
A number of EP engine types have beendeveloped for years. Ions are accelerated byelectro-thermal, electro-static, electro-magneticand combined forces in the thruster. The
performance of an EP engine is evaluated bythrust F, specific impulse Isp and thrust efficiency
. The ion engine is operated with high Isp and in spite of low thrust and is used in long term
missions. A Magneto-Plasma-Dynamic thruster
and a Hall thruster have larger thrust andapplication to manned flight mission is expected.
Although the EP system is requisite for long term
mission, electrode erosion in the thruster is one of
the serious problems restricting thruster operationtime.
In the further development of space explorationthe EP engines with a higher specific impulse anda larger thrust are necessary. With the increase of
requiredelectricpower,utilizationofelectromagnetic (EM) waves not only in plasma

production but in ion acceleration is expected toavoid serious damage in electrodes. A number of
researches have started to develop ion
acceleration methods using EM waves, andJapanese activities contributes to this field, such
as VASIMR, Double layer (DL), rotating EM
field, microwave beaming propulsion.
Here, an investigation of electrode-less ion
acceleration in EP systems using EM waves willpresented and tasks for further investigation inhigh power EP systems will be discussed.
2. Ion acceleration by EM waves
An ion acceleration by the combination of ion
cyclotron heating and magnetic nozzle has been
investigated related to the Variable Specific
Impulse Magnetoplasma Rocket (VASIMR)
project [4], which is expected to be a main engine
for manned flight to Mars. The accelerated ion
energy could be controlled by the input RF power
only, which has been successfully demonstrated
in the HITOP experiments [5-7]. Recent progressof the VX-200 device in Ad Astra Rocket Co.
reveals high potential of this engine. More than
5N of thrust was obtained at 200kW of radio
frequency (RF) power with the efficiency of 72%[8].
A Helicon Double Layer Thruster (HDLT)
utilizes a current-free electric double layer. The
electrical potential is much higher inside the source
region than in the exhaust. The large potential gap
is feasible to confine most of the electrons and toaccelerate the ions away from the source. This
creates an accelerating electric field without
inserting unreliable components like high voltage

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grids into the plasma. Low power HDLT has beendeveloped and physical mechanism of DLformation was investigated [9.10].
Direct plasma acceleration using a rotatingtransverse electric field has been investigated in
Lissajous Helicon Plasma Accelerator (LHPA) [11].
When the frequency for the applied rotational
electric field is in the range between ci<< <<ce,only electrons rotates azimuthally and generates
azimuthal currents j. The thrust is produced due tothe Lorentz force j × Br, where Br is formed byexpanding magnetic field. Experiments has been
started to excite rotating field in plasmas.
Utilization of rotating transverse magnetic field or
ponderomotive force of EM waves is also proposed
and numerical investigations have been performed[12].
Microwave can be utilized not only in plasma
production but in plume acceleration. The
microwave beaming propulsion was investigated inTokyo Univ. and JAEA [13]. Microwave beamfrom 170GHz gyrotron was irradiated to a projectile
and ionization front of atmospheric plasma wasinvestigated. The propagation velocity of theionization front was found to be supersonic. With arepetitive pulses the projectile was launched by thecounterforce of the exhaust plume. No energy
source and propellant is necessary on board in thebeaming propulsion and it is expected to achieve a = ci

RF heatingplasmaproduction

Magneticnozzle(a) VASIMR type thruster

HeliconplasmaDoublelayer(b) HDL type thrusterj

Rotating
electric field(c) LHPA type thruster

Fig.1. Schematic of several types of plasma
thrusters using RF power.

higher payload ratio than conventional chemicalrockets.
3. Future tasks in EP systems with EM waves
In acceleration by EM waves, besides of noelectrode, an additional advantage is that noneutralizer (electron emitter) is necessary, since theacceleration occurs in a plasma and equal numbersof electron and ions are emitted from the source.
As most of the acceleration occurs with amagnetic field, the plasma detachment from thefield is one of the important problems to be solved.
Ions can escape from the field due to their large
Larmor radius, but electrons remains to be captured
in the field. The charge separation occurs and anelectric field appears to decelerate ions.
In the further activities for high power thruster,utilization of EM waves in plasma production andacceleration will be pursued in many types of EP
systems. To avoid large power loss in conversion
from DC to RF, reliable and efficient power sourcesof EM waves are also required to be developed.
Most of the proposed thrusters using EM waves
work with an axial magnetic field. Powerconsumption and mass of the magnetic coils should
be considered in total evaluation of the propulsion
system.
References[1] R.H. Frisbee, J. Propulsion and Power, 19 (2003)
1129.
[2] H. Kuninaka et al., J. Propulsion and Power, 14,(1998) 1022.
[3] A. Fujiwara, et al., Science 312 (2006) 1330.
[4] F.R.ChangDiaz, et al., Proc. of 36th Joint Propulsion
Conference, AIAA-2000-3756 (2000).
[5] M.Inutake, et al, Plasma Phys. Control. Fusion, 49(2007) A121.
[6] A. Ando, et al., Plasma and Fusion Research, 3(2008) S1018.
[7] A. Ando, et al., Trans. Fusion Science and Tech., 51
FUSTE8 (2007) 72.
[8] J.P. Squire, et al., Proc. of 32nd International
Electric Propulsion Conference, IEPC-2011-154(2011).
[9] C. Charles and R.W.Boswell App. Phys. Lett. 82(2003) 1356.
[10] K.Takahashi, et al, App. Phys. Lett. 97 (2010)
141503.
[11] K.Toki, et al., J. Plasma Fusion Res. SERIES 8(2009) 25.
[12] S.Shinohara, et al., Proc. of 32nd International
Electric Propulsion Conference, IEPC-2011-056(2011).
[13] Y.Oda, K.Komurasaki, et al., J. Appl. Phys., 100(2006) 113307.

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