American Institute of Aeronautics and Astronautics092407
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On the Electrodeless MPD Thruster Using a CompactHelicon Plasma Source
Kyoichiro Toki 1
Tokyo University of Agriculture and Technology, Tokyo, JapanE-mail: [email protected]
Shunjiro Shinohara2
Kyushu University, Fukuoka, Japan
Takao Tanikawa3
Tokai University, Kanagawa, Japan
Tohru Hada4
Kyushu University, Fukuoka, Fukuoka, 816-8580, Japan
Ikkho Funaki5
Japan Aerospace Exploration Agency, Kanaagwa, Japan
Yoshikazu Tanaka6
Tokyo University of Agriculture and Technology, Tokyo, Japan
Akihiro Yamaguchi7
Tokyo University of Agriculture and Technology, Tokyo, Japanand
Kostiantyn P. Shamrai8
Institute for Nuclear Research, Kiev, Ukraine
Helicon wave excitation is one of the promising RF plasma production methods. Itproduces high density plasma (~1013 cm-3) that enables electromagnetic acceleration. Weprepared the acceleration coil or 2 pairs of copper plates around the glass tube. Theseacceleration methods are called a repetitious coil current acceleration and a continuous“Lissajous” acceleration, respectively. When the repetitious coil acceleration was applied,the maximum plasma velocity of 3.6 km/s was 76% velocity increment compared with beforeacceleration with the absorbed plasma production + acceleration power of (400+180) W andthe applied magnetic field strength of 1,450 gauss. As for the “Lissajous” acceleration, theplasma velocity was 2.2 km/s with the absorbed plasma production + acceleration power of(290+200) W. However it is suggested that these accelerations remain in the thermalacceleration regime judging from the electron temperature or density increase.
1 Professor, Mechanical Systems Engineering, 2-24-16 Naka-cho, Koganei-city, Tokyo 184-8588, Member AIAA.2 Associate Professor, Interdisciplinary Graduate School of Engineering Sciences, 6-1 Kasuga-Kohen, Kasuga, Fukuoka 816-8580, Non-member.3 Professor, Research Institute of Science and Technology, 1117 Kitakaname, Hiratsuka, Kanagawa 259-1292, Non-member.4 Associate Professor, Interdisciplinary Graduate School of Engineering Sciences, 6-1 Kasuga-Kohen, Kasuga, Fukuoka 816-8580, Non-member.5 Associate Professor, Institute of Space and Astronautical Science, 3-1-1 Yoshinodai, Sagamihara, Kanagawa 229-8510,Member AIAA6 Graduate student, Mechanical Systems Engineering, 2-24-16 Naka-cho, Koganei-city, Tokyo 184-8588, Non-member.7 Undergraduate student, Mechanical Systems Engineering, 2-24-16 Naka-cho, Koganei-city, Tokyo 184-8588, Non-member.8 Head, Department of Plasma Theory, National Academy of Sciences, 47 Prospect Nauki, Kiev 03680, Non-member.
This work is supported by JSPS Grant-in-Aid for scientific research (A).
American Institute of Aeronautics and Astronautics092407
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NomenclatureB = magnetic fieldu = velocitye = electronic chargeE = electric fieldI = probe currentJ = currentm = ion, neutral and electron masst = timeν = collision frequencyω = angular velocitySubscripts0 = initiale = electronela = elastici = ioninela = inelasticpara = pararellperp = perpendicularx = x directiony = y directionz = z direction
I. IntroductionHE electric propulsion has attracted keen attention with increasing applications in space because they are ableto save propellant consumption compared with chemical propulsion rockets. Also, the electric propulsion can
procure their propulsive energy by solar cells over a long-term flight. For these reasons, the electric propulsion areemployed for long-term mission, such as interplanetary flight and satellite attitude control. This implies that theelectric propulsion is required a long lifetime in order to keep working for many years.
The electrodeless configuration is one of the long lived electric propulsion solutions,1-2 such as VASIMR(Variable Specific Impulse Magnetoplasma Rocket). This plasma source based on the helicon plasma excitationwhich is one of the RF plasma production method.3-4 The VASIMR also employs a magnetic nozzle accelerationdependent on ICRH (Ion Cyclotron Resonance Heating) as the plasma energization, hence VASIMR can avoiddeterioration of the engine caused by electrode errosion.5 However, the acceleration principle is based upon “plasmaheating” and “passive nozzle expansion” categorized into an electrothermal regime. Here, we would like to proposean “electrodeless electromagnetic acceleration” in a small thruster than the large electrodeless rocket like VASIMR.
This paper describes a new type of small electrodeless electromagnetic thruster. We use a compact heliconplasma source to maintain high density plasma (~1013 cm-3) that may enable electromagnetic acceleration. Wealready successfully established a helicon mode plasma in a 2.5 cm i.d. glass tube.6-8 The plasma accelerationmethods are divided into three categories. They are electrostatic or electromagnetic acceleration in addition toelectrothermal acceleration such as VASIMR. Our plasma acceleration is based on electromagnetic principle.5-10 Weemployed two types of plasma acceleration methods using the coil or RF antenna. These acceleration methods arecalled a repetitious coil current acceleration and a continuous “Lissajous” acceleration.
II. Principle of Plasma AccelerationA. Repetitious Coil Current Acceleration
The first approach is the coil current acceleration that induces diamagnetic current in the azimuth direction andits amplitude is proportional to the time gradient of the applied magnetic field induced by the acceleration coilhaving a saw-tooth current waveform. When the Lorentz force acts as an acceleration force in certain period, theplasma is compressed and directly accelerated toward downstream direction while the plasma is decelerated duringthe reversed coil current. In order to prevent cancellation of acceleration with deceleration force, we took advantageof the difference of the skin time between the acceleration phase and the deceleration phase. The decelerationcurrent decreases rapidly, while the acceleration current increases slowly. In this process, the deceleration force acts
American Institute of Aeronautics and Astronautics092407
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Electro Magnetic Coil
Ar gas
SADDLE Antenna
RF Antenna
Glass tube
Ar Plasma exhaustz
xy
Electro Magnetic Coil
Ar gas
SADDLE Antenna
RF Antenna
Glass tube
Ar Plasma exhaustz
xy
z
xy
only plasma periphery and the acceleration force actsthe core plasma. Ultimately, the ideal wave form isshown in Fig.1.
B. Continuous “Lissajous” AccelerationSecondly, we proposed 2 pairs of deflection plates
around the glass tube applying rotating electric field soas to induce electron current continuously in azimuthdirection inside the cylindrical plasma. The ion currentis little induced because of the larger inertia. This is“Lissajous” acceleration but this approach has animportant assumption of the electric field penetrationinto high density plasma. The plasma equation ofmotion in this “Lissajous” acceleration is expressed asthe following Langevin equations.
(1)
(2)
Here, x, y, z are the coordinates depicted in Fig. 2and ω0 = eB/m. The solution of these differentialequations includes a general solution decaying exponentially by -ν �t and then only a special solution is valid andfinally remained as expressed below.
(3)
(4)
(5)
(6)
Apparently the ions and electrons gain rotational velocity and power around z-axis by rotating applied electricfields of Ex and Ey as long as the collision frequency ν remains in a finite value. The collision frequency mustinvolve elastic νela and inelastic νinela collisions especially with charge exchange collisions νcex.
(a) Schematic of “Lissajous” acceleration device. (b) Concept of Rotation Electric field.
Fig. 2. Principle of a Continuous “Lissajous” Acceleration.
Electro Magnetic Coil
Ar gas
SADDLE Antenna
Acceleration Coil
Glass tube
Ar Plasma exhaustz
xy
Electro Magnetic Coil
Ar gas
SADDLE Antenna
Acceleration Coil
Glass tube
Ar Plasma exhaustz
xy
z
xy
J
Jθ
B
B× Jθ
J
Jθ
B
B× Jθ J
Sa Sb
SJ
Sa SbSa Sb
S
(b) J induced in plasma. (c) A saw-tooth current for the Coil.
(a) Schematic of Coil acceleration device.
Fig. 1. Principle of a repetitious coil current acceleration.
American Institute of Aeronautics and Astronautics092407
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III. Procedure for ExperimentA. Experimental Devices
Our compact helicon source consists ofplasma production part, plasma accelerationpart and vacuum system part. 2.5 cm i.d. withtotally about 30 cm long pyrex glass tubeconnected to a vacuum chamber (Fig. 3). Argas flows from a metallic end plate with a gasport to the vacuum chamber. The plasmaproduction and acceleration power is appliedwhile Ar gas flows along the glass tubetoward the vacuum chamber. A double saddletype (Boswell type) antenna is used forplasma production, and wound a 47 turnacceleration coil or otherwise a pair ofacceleration antennae downstream. Thevacuum pump evacuated the vacuumchamber down to 0.1 Pa (1 mTorr) or lower,and the Ar gas is fed by a mass flowcontroller Brooks 5850E at a predeterminedmass flow rate, 0.5 mg/s corresponding tothe background pressures of 0.1 Pa (1 mTorr).A 489 turn coil magnet produces 38 gauss/A up to 1,450 gauss maximum in the midst of coil bobbin. A signalgenerator of HP-8657A and a 700 W amplifier of Thamway T145-5768A with a matching box T020-5558A at thefrequency 27.12 MHz for plasma production, and T145-5536 with T020-5536A for 300 W acceleration amplifierwith frequency range of 1-16 MHz max were used for RF power source. When adopted a continuous Lissajousacceleration, two RF signals feed from Function Generator of 1ch and 2ch. Dual RF amplifier and dual matchingbox is necessary for each RF signals.
B. Probe for Measuring Plasma VelocityWe use Mach Probe shown in Fig. 4.11 The Mach probe comprises two direction tips facing parallel and
perpendicular to the plasma flow. Our Mach probe was made from 1.5 mm diam. copper rods with 45 degreestapered surfaces, the one parallel and the other perpendicular to the flow. These rods are covered by 2 mm in diam.ceramic tubes. Here, ion acoustic Mach number Mi is defined by ratio of plasma velocity to the ion acoustic velocityCs.
(7)
The ion acoustic Mach number Mi is expressed as ratio of ion saturation currents collected by two probe tips.
(8)
(9)
Where, is dependent on the ratio of Ti/Te. In a supersonic flow (Mi>1), the Eq.(8) is used. But, in a subsonicflow (Mi<1), the Eq.(9) is used.
To avoid the probe interaction with the plasma ignition, the ceramic insulator as thin as 2 mm o.d. diam. tubewas used. The probe voltage was applied by battery from -60 to +60 V. The probe current was measured by a simpleresistor. Both the probe voltage and current traces are recorded by an Omniace RA1200 digital recorder and thenanalyzed by a personal computer. The electron temperature was evaluated from the gradient of probe curve near thefloating potential and the plasma density was estimated from the ion saturation current.
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To improve measurement accuracy, we developed probe assembly driver. A drive probe rotate around the edgeof mach probe and position at the angle of 0 or 90o degrees expressed in Fig.4. It enables to estimate the ratio ofprobe tips area with sheath region. We used a stepper motor, and setup the angle and rotation speed by a controller.Thus, we can obtain the tip area ratio by using this assembly. If the ratio of ion saturation currents at the angle of 0o
is equal to that of 90o , the equation of relation is expressed below.
(10)
Here, Sa, Sb is the area of probe tip a and b, respectively as shown in Fig.4. Consequently, the ratio of probe tipsarea is expressed below.
(11)
By applying Eq.(11), we obtain the ratio of Ipara and Iperp with high precision.
Fig. 4 Mach probe rotates around the centerline of the plasma.
IV. Experimental ResultsFirstly, the axial and radial magnetic field intensity were measured by gauss meter shown in Fig.5 and Fig.6. In
Fig.5, axial distance of 0 mm is the edge of double saddle type antenna set-up point and axial distance of 20 mm isin the midst of coil bobbin. Magnetic field intensity at the acceleration point (90 mm) is 800 gauss. On the otherhand, the maximum of radial magnetic field intensity is 330 gauss.
A. Repetitious Coil Current Acceleration ResultsFigures 7-10 exhibit the results of plasma velocity measurement for various acceleration powers up to about 180
W using our Mach probe. The tips of this Mach probe was placed along the centerline of glass tube about 6.5 cmdownstream position from the edge of the acceleration coil. The 47 turn coil for plasma acceleration is wound
0IS
S
I
I
a
b
perp
para =⋅ 90IS
S
I
I
b
a
perp
para =⋅
0
90
b
a
I
I
S
S =
Angle 0� Angle 90�
Ipara, Sa
Iperp, Sb Ipara, Sb
Iperp, Sa
Plasma flow
Mach Probe
Angle 0� Angle 90�
Ipara, Sa
Iperp, Sb Ipara, Sb
Iperp, Sa
Plasma flow
Mach Probe
0200400600800
1000120014001600
0 20 40 60 80axial distance [mm]
Mag
neti
cfi
eld
inte
nsit
y[G
]
0200400600800
1000120014001600
0 20 40 60 80axial distance [mm]
Mag
neti
cfi
eld
inte
nsit
y[G
]
0
50
100
150
200
250
300
350
-60 -40 -20 0 20 40 60
radical distance [mm]
Mag
neti
cfi
eld
inte
nsit
y[G
]
0
50
100
150
200
250
300
350
-60 -40 -20 0 20 40 60
radical distance [mm]
Mag
neti
cfi
eld
inte
nsit
y[G
]
Fig. 5 Axial direction of magnetic field intensity. Fig. 6 Radial direction of magnetic field intensity at connectionbetween glass tube and vacuum chamber.
American Institute of Aeronautics and Astronautics092407
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around the 2.5 cm glass tube. A repetitious coil current acceleration is performed under the chamber pressure of 0.10Pa, Ar gas flow rate of 0.4 mg/s, the absorbed plasma production power of 400 W at a frequency of 27.12 MHz, aplasma acceleration frequency for the coil of 6 MHz, the applied magnetic field strength of 1450 gauss.
The plasma velocity, electron temperature, plasma density and Ipara/Iperp measured by our mach probe are shownin Fig. 7- Fig. 10. The Blue and pink plots are the data for the probe angle of 0o and 90o degrees, respectively. Thelight blue line implies the average of measured data at 0o and 90o. Figure 7 shows plasma velocity increase, as theapplied acceleration power increases. The plasma velocity was raised by 76 % increment compared with the valuebefore acceleration at the max power of 180 W. Similarly, the more the applied acceleration power increases, themore the electron temperature increases. At the max power of 180 W, it indicates about 2.2 times increase comparedwith before acceleration. This implies the increment of plasma velocity is thermally obtained. On the other hand, theplasma density is decreased when applied plasma acceleration power. The Ipara/Iperp showed almost no changebetween before and after acceleration. However, beyond 150 W of acceleration power applied, it seems to beslightly decreasing. This strange behavior has not been solved yet.
When we adopted a repetitious coil current acceleration method, the RF power was absorbed into electrons toraise the electron temperature and this means a passive plasma acceleration. Our final goal is to have plasmaelectromagnetically accelerated. At present, we found that the major reason of insufficient electromagneticacceleration is due to the incomplete formation of the saw-tooth wave form. The required steep gradient of thedeceleration period is moderated by the matching frequency of the matching box. The coil current through thematching box, the saw-tooth wave form changes into a sinusoidal wave form. We should solve this problem in thenext step.
0.0E+00
2.0E+10
4.0E+10
6.0E+10
8.0E+10
1.0E+11
1.2E+11
1.4E+11
0 30 60 90 120 150 180
0°
90°
avePla
sma
Den
sity
[cm
-3]
Net absorbed acceleration power
0.0E+00
2.0E+10
4.0E+10
6.0E+10
8.0E+10
1.0E+11
1.2E+11
1.4E+11
0 30 60 90 120 150 180
0°
90°
avePla
sma
Den
sity
[cm
-3]
Net absorbed acceleration power
Fig. 9. Plasma density of a repetitious coil currentacceleration at each absorbed RF power.
11.11.21.31.41.51.61.71.8
0 30 60 90 120 150 180
I par
a/I p
erp
Net absorbed acceleration power
11.11.21.31.41.51.61.71.8
0 30 60 90 120 150 180
I par
a/I p
erp
Net absorbed acceleration power
Fig. 10. Ipara/Iperp of a repetitious coil current acceleration.at each absorbed RF power.
2500
2700
2900
3100
3300
3500
3700
3900
0 30 60 90 120 150 180
0°
90°
avePlas
ma
Vel
ocit
y[m
/s]
Net absorbed acceleration power
2500
2700
2900
3100
3300
3500
3700
3900
0 30 60 90 120 150 180
0°
90°
avePlas
ma
Vel
ocit
y[m
/s]
Net absorbed acceleration power
Fig. 7. Plasma velocity measurement of a repetitious coilcurrent acceleration at each absorbed RF power.
0
2
4
6
8
10
12
0 30 60 90 120 150 180
0°
90°
ave
Net absorbed acceleration power
Ele
ctro
nT
empe
ratu
re[e
V]
0
2
4
6
8
10
12
0 30 60 90 120 150 180
0°
90°
ave
Net absorbed acceleration power
Ele
ctro
nT
empe
ratu
re[e
V]
Fig. 8. Electron temperature of a repetitious coil currentacceleration at each absorbed RF power.
American Institute of Aeronautics and Astronautics092407
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B. Continuous “Lissajous” Acceleration ResultsFigure 11 shows an acceleration antenna for “Lissajous” acceleration. Rotating electric field is made with two
pairs of this antenna. Figures 12-14 exhibit the result of measured plasma velocity, electron temperature and plasmadensity by our mach probe. The tips of the mach probe is placed 6.5 cm downstream location from the edge of theantennae and rotated at the position. We adopted a continuous “Lissajous” acceleration under the conditions of thechamber pressure of 0.13 Pa, Ar gas flow rate of 0.5 mg/s, the absorbed plasma production power of 290 W atfrequency of 13.56 MHz, the absorbed plasma acceleration power of 200 W at frequency of 15 MHz and the appliedmagnetic field strength of 1,450 gauss.
The measured data are shown in the figure of the continuous“Lissajous” acceleration results. The blue and pink plots are the datawhich represent the probe angle of 0o and 90o degrees, respectively.The light blue line in the figures is average of measuring data at 0o
and 90o probe positions and dotted line denotes the case appliedonly plasma production power. When taking a look at the plasmavelocity, it was recognized that the plasma velocity was increasedby 50% compared to the before acceleration and resulted in 2.2 km/s.This is not satisfactory result because our goal in this power level is14 km/s corresponding to 50% thrust efficiency. This result impliesthat fairy amount of the RF power of acceleration was absorbed intoplasma production or dissipated into the atmosphere.
(a) Deployed view. (b) Rolled onto the glass tube.
Fig. 11 The acceleration antenna for “Lissajous” experiment.
American Institute of Aeronautics and Astronautics092407
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The electron temperature revealed small decrease at all phase differences. This indicated that the power foracceleration was not absorbed as the increment of electron temperature. On the contrary, the plasma density showedslight increase at all phase differences. This result implies that the plasma was created if the applied RF power ofacceleration, or other factors like plasma space potential have some effects on this measurement. The principle ofcontinuous “Lissajous” acceleration is based on plasma rotational drift motion. Since the electron rotation isrealized by this drift motion, the electromagnetic acceleration may not take place if the collision between theelectrons and neutrons / ions under this pressure. To avoid this situation, we should maintain the glass tubeacceleration region at higher vacuum condition than ever. This problem would be solved to set as low Ar gas flowrate as possible, to place whole the device inside the vacuum chamber, or to increase the magnetic field intensity.And we need to ascertain the best shape of RF antenna for the plasma electromagnetic acceleration attemptingvarious RF matching conditions for higher absorption efficiency.
Figure 15 is an experiment of a repetitious coil current acceleration. In the midst of the right picture, the plasmaemits blue light. This is thought as the helicon wave excited plasma because its density is over 1013 cm-3 at this pointfrom the previous experiment. In this experiment, the acceleration power was absorbed into the electron.
V. ConclusionWhen we adopted a repetitious coil current acceleration method, the maximum plasma velocity was 3.6 km/s. It
was 76 % velocity increment compared with before acceleration under the chamber pressure of 0.10 Pa, Ar gas flowrate of 0.4 mg/s, the absorbed plasma production and acceleration power of (400+180) W, the coil of 47 turns andthe applied magnetic field strength of 1,450 gauss. However, the electron temperature was raised up to about 2.2times higher than the value before acceleration. This implies that the increment of plasma velocity is thermally.
When we adopted the continuous “Lissajous” acceleration method, the plasma velocity was 2.2 km/s under thechamber pressure of 0.13 Pa, Ar gas flow rate of 0.5 mg/s, the absorbed plasma production and acceleration powerof (290+200) W, the coil of 47 turns and the applied magnetic field strength of 1,450 gauss. A fairy amount of thepower for acceleration might be absorbed into plasma density increase and the dissipation into the atmosphere.
For the repetitious coil current acceleration method, to produce the saw-tooth current for the coil is the keyfactor. For a continuous “Lissajous acceleration method, to avoid the collision between the electron and neutron /ions is next assignment. We should put efforts on these significant challenges in the next step.
References1Shamrai, K. P., Aleksandrov, A. F., Bougrov, G. E., Virko, V. F., Katiukha, V. P., Koh, S. K., Kralkina, E. A., Kirichenko,
G. S. and Rukhadze, A. A., "Quasistatic Plasma Sources: Physical Principles, Modelling Experiments, Application Aspects",Journal of Physics IV, France 7, 1997, C4, 365-381.
2Toki, K., Shinohara, S., Tanikawa, T., Funaki, I. and Shamrai, K. P., “Preliminary Investigation of Helicon Plasma Sourcefor Electric Propulsion Applications”, IEPC 03-0168, Proceedings of the 28th International Electric Propulsion Conference,Toulouse, France, 17-21 March, 2003.
Fig. 15. Experiment of a repetitious coil current acceleration under the pressure of 0.10 Pa, Ar gas flow rate of 0.4 mg/s,plasma production frequency and absorbed power of 27.12 MHz and 400 W, magnetic field strength of 1,450 gauss,plasma acceleration frequency and absorbed power of 6 MHz and 180 W.
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3Shinohara, S., “Recent Topics on High Density Plasma Production by Helicon Waves”, Journal of Plasma and FusionResearch, Vol. 78, No. 1, pp. 5-18, January 2002.
4Charles, C., Boswell, R., Alexander, P., Costa, C., Sutherland, O., Pfitzner, L., Franzen, R., Kingwell, J., Parfitt, A., Frigot,P., Gengembre, J. E. and Saccoccia, G., “Helicon Douoble Layer Thrusters”, AIAA-2006-4838, 42nd AIAA/ASME/SAE/ASEEJoint Propulsion Conference & Exhibit, Sacramento, CA, July 9-12, 2006.
5Squire, J. P., Chang Diaz, F. R., Jacobson, V.T., McCaskill, G. E., Bengston R. D. and Goulding, R. H., "Helicon PlasmaInjector and Ion Cyclotron Acceleration Development in the VASIMR Experiment", AIAA 2000-3752, 36thAIAA/ASME/SAE/ASEE Joint Propulsion Conference, 17-19 July 2000, Huntsville, Alabama, USA.
6Toki, K., Shinohara, S.,Tanikawa, T. and Shamrai, K. P., "Small helicon plasma source for electric propulsion", ELSEVIER,Thin Solid Films, Vol. 506-507, September 2005, pp. 597-600.
7Toki, K., Shinohara, S., Tanikawa, T., Funaki, I., Shamrai, K. P., Hashimoto, T., Makita, K. and Ikeda, Y., “Study ofElectrodeless Plasma Production and Electromagnetic Acceleration”, ISTS 2006-b-45, Proceedings of the 25th InternationalSymposium on Space Technology and Science (ISTS) , Kanazawa, Japan, 2006, pp. 298-303.
8Toki, K., Hashimoto, T., Makita, K., Shinohara, S., Hada, T., Ikeda, Y., Tanikawa, T., Shamrai, K. P. and Funaki, I., “SmallHelicon Source for Electrodeless Plasma Production and Electromagnetic Acceleration”, AIAA-2006-4843, 42ndAIAA/ASME/SAE/ASEE Joint Propulsion Conference & Exhibit, Sacramento, CA, July 9-12, 2006.
9Toki, K., Hashimoto, T., Tanaka, Y., Shinohara, S., Hada, T., Ikeda, Y., Tanikawa, T., Shamrai, K. P. and Funaki, I.,“Compact Helicon Source Experiments for Electrodeless Electromagnetic Thruster”, AIAA-2007-5260, 43ndAIAA/ASME/SAE/ASEE Joint Propulsion Conference & Exhibit, 8-11 July, 2007.
10Tanaka, Y., Toki, K., Shinohara, S., Hada, T., Tanikawa, T., Funaki, I., Shamrai, K. P., “Plasma ElectromagneticAcceleration with Antenae in Small Helicon Source”, ISTS 2008-b-48, 26th International Symposium on Space Technology andScience (ISTS) , Hamamatsu, Japan, June 2008.
11Ando, A., Watanabe, T., Watanabe, T., Tobari, H., Hattori, K. and Inutake, M., “Evaluation of Para-Perp Type Mach Probeby Using a Fast Flowing Plasma”, Journal of Plasma and Fusion Research, Vol. 81, No. 6 (2005), pp. 451-457.
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