田原 弘一

ホール型イオンエンジン性能への磁場・加速チャネル構造の影響。(担当部分：作動実験、取りまとめ)

アルゴン空気混合熱プラズマＣＶＤ法による酸化物成膜の研究。(担当部分：作動実験、取りまとめ)

宇宙飛翔体表面繰り返し放電現象の特性とその数値計算の研究。(担当部分：作動実験、取りまとめ)

小型衛星用シリンドリカル型ホールエンジンの磁場の効果の研究。(担当部分：作動実験、取りまとめ)

超小型衛星用電熱加速型パルスプラズマエンジンの開発研究。(担当部分：作動実験、取りまとめ)

In magneto-plasma-dynamic (MPD) arcjet generators, plasma is accelerated by electromagnetic body forces. Silicon nitride reactive spraying was carried out using an MPD arcjet generator with crystal silicon rods and nitrogen gas. Because higher-velocity, higher-temperature and higher-density and larger-area plasmas are produced with the MPD arcjet generator than those with conventional thermal plasma torches, nitriding of silicon can be enhanced. A dense and uniform β-Si3N4 coating with 30 μm in thickness was formed after 200 shots at a repetitive frequency of 0.03 Hz with a discharge current of 9 kA and a substrate temperature of 700 ℃. The Vickers hardness reached about 1300. Furthermore, silicon carbide and aluminum nitride sprayings were conducted with some spraying systems. All results showed that the MPD arcjet generator had high potentials for spraying.

In magneto-plasma-dynamic (MPD) arcjet generators, plasma is accelerated by electromagnetic body forces. Silicon nitride reactive spraying was carried out using an MPD arcjet generator with crystal silicon rods and nitrogen gas. Because higher-velocity, higher-temperature and higher-density and larger-area plasmas are produced with the MPD arcjet generator than those with conventional thermal plasma torches, nitriding of silicon can be enhanced. A dense and uniform β-Si3N4 coating with 30 μm in thickness was formed after 200 shots at a repetitive frequency of 0.03 Hz with a discharge current of 9 kA and a substrate temperature of 700°C. The Vickers hardness reached about 1300. Furthermore, silicon carbide and aluminum nitride sprayings were conducted with some spraying systems. All results showed that the MPD arcjet generator had high potentials for spraying.

The cylindrical Hall thruster (CHT) is an attractive approach to achieve a long lifetime thruster operation especially in low power space applications. Because of the larger volume-to-surface ratio than conventional coaxial Hall thrusters, the cylindrical Hall thrusters are characterized by a reduced heating of the thruster parts and potential lower erosion. Existing CHTs can feature a short coaxial channel in order to sustain a high ionization in the thruster discharge. A 5.6 cm diameter cylindrical Hall thruster was developed and operated with and without a short coaxial region of the thruster channel, in the power range of 70-300 W. It is shown that the CHT without coaxial region can operate stable and achieve higher thrust efficiency, 22%-32% more than that with a coaxial region. Plasma probe measurements inside the thruster channel and ion energy measurements in the plasma plume suggest that the ionization/ acceleration region in the CHT is located near the anode region where a radial magnetic field is stronger. © 2007 American Institute of Physics.

In order to improve wear resistance of atmospheric thermal plasma sprayed molybdenum (Mo) coating, diamond deposition on the atmospheric plasma sprayed molybdenum coating by the combustion flame chemical vapor deposition (CFCVD) has been operated. Although diamond particles could be deposited on the molybdenum coating, the coating was fractured and peeling off due to thermal influences in our previous study. In this study, to diminish the thermal damage of the substrate during operation, a thermal insulator was equipped between substrate and water-cooled substrate holder. Consequently, diamond particles could be created on the Mo coating without fracture and peeling off. From these results, it was found that this process had a high potential in order to improve wear resistance of thermal sprayed coating.

In the future, LEO spacecraft will be larger and higher powered. Because of the balance of the leakage currents through the ambient space plasma, their main conductive body will have a higher negative potential without plasma contactor operation. When the spacecraft operates with a higher voltage, more intensive arcing is suspected to occur on the surface. In this study, a ground-based experiment was carried out to understand the arcing phenomenon and to examine the influences of the ambient space plasma on the arcing process. Simulating plasmas were generated by electron-cyclotron-resonance discharge. When arcing occurred on negatively biased anodized-aluminum-sample (AAS) plates in the plasma environment, the time variations in the arc current and bias voltage were measured. The arc-spot diameter was also measured. The single-arcing characteristics showed that both the peak arc current and the total charge emitted by arcing increased with the initial-charging voltage and neutral-particle number density. The diameter of the arc spot increased with the initial-charging voltage although it was almost constant regardless of the neutral-particle density. The repetitive-arcing characteristics showed that the arc rate gradually increased with the arcing number. Lots of overlapping arc spot were observed after 1000 arcings, and its number increased with the arcing number. The influences of the initial-charging energy on arcing characteristics were also examined by widely changing the capacitance and the initial-charging voltage. The arc-spot diameter intensively increased with the initial-charging energy, and the fitting line could be evaluated. Accordingly, a high-voltage operation of the LEO spacecraft might bring a drastic degradation of AAS by arcing, depending on the ambient plasma conditions and spacecraft capacitance. © 2006 IEEE.

The effects of channel wall material on Hall thruster performance and on plasma characteristics were investigated. A laboratory-model Hall thruster THT-III was operated with three channel wall materials of BN, BNSiN and BNAlN. Both the discharge current and the thrust were affected by the nature of the channel wall materials. The measured axial distributions of wall and plasma potentials, radial and axial electron temperatures, and electron number density near the channel walls showed that the wall material affected ionization region and ion wall loss in the channel, resulting from secondary electron emission, although ion acceleration region was determined by the axial distribution of radial magnetic field. The difference in discharge current between channel wall materials was attributed to the difference in axial current density near the inner channel wall, depending on secondary electron emission. © 2006 Elsevier Ltd. All rights reserved.

A pulsed plasma thruster (PPT) with a propellant feeding mechanism was designed using two poly tetrafluoroethylene (PTFE) bars as propellants. The PPT was mounted on a thrust stand with a 1-m-long perpendicular pendulum which was developed for precise measurements of impulse bits. Initial thrust performance showed thrust-to-power ratio of 43-48 μN/W, specific impulse of 470-500 s and thrust efficiency of 10-12% with energy of 4.5-14.6 J. Ten thousand shots achieved a total impulse of approximately 3.6 Ns, and the PTFE bars were consumed approximately 2 mm in length. However, uneven receding of the PTFE surface was observed. In order to investigate physical phenomena in a whole system, an unsteady numerical simulation of initial discharge, generation of plasma, heat transfer to the PTFE, heat conduction inside the PTFE, ablation from the PTFE surface and acceleration of plasma was performed. The calculated results were used to explain the physical phenomena in the cavity, especially ablated mass of the PTFE. © 2006 Elsevier Ltd. All rights reserved.

TiO2 film were deposited by atmospheric thermal plasma chemical vapor deposition (TPCVD) method to investigate the rapid process for functional film deposition. The experiment was conducted under the condition where working gas was At, working gas flow rate was 20 l/min, deposition distance was varied from 30 to 200 mm and spraying time was 10 min. Ethanol diluted titanium tetra buthoxide was used as starting material. Consequently, even in this process TiO2 films including anatase could be deposited, and the results of wettability and methylene blue decoloration testings suggest that the TiO2 films have good photo-catalytic property. Besides, by using extension nozzle, columnar structure film could be deposited due to a perfect starting material vaporization. From these results, the proposed process seemed to be highly promising for the rapid formation of functional thin films. (c) 2006 Elsevier Ltd. All rights reserved.

In order to develop a functional film deposition process with high deposition rate, as a basic study, deposition of titanium oxide (TiO2) and zinc oxide (ZnO) films by thermal plasma chemical vapor deposition (CVD) in the air was carried out. As ingredient, ethanol-diluted titanium tetra butoxide and zinc acetate solution were used for TiO2 and ZnO deposition, respectively. To investigate the effects of feedstock concentration on the films' structures and photocatalytic property, film deposition with various concentration of feedstocks and photocatalytic tests (i.e., wettability test and methylene-blue decoloration test) were conducted. Consequently, in the cases of both films' deposition, as the case of the CVD process, film structure could be changed from particle accumulated to columnar by decreasing the zinc acetate/ ethanol ratio. Not only crystallized film but also amorphous film could be deposited, depending on deposition distance. In the case of crystallized film, photocatalytic properties were confirmed in the films by the methylene-blue decoloration test and wettability test. When the TiO2 film was applied to the photoelectronics device of dye-sensitized solar cell, the cell could generate an electromotive force of 0.13 V, which was almost the same voltage as the ready-made one. From these results, this process was found to have a high potential for a high-rate functional film deposition process conducted in the air.

For a Hall thruster, the influences of discharge channel wall material on thrust performance and plasma characteristics in the vicinity of the channel wall were investigated. In this study, THT-III 1-kW class Hall thruster was operated with three dielectric channel walls of BN, BNAlN and BNSiN. Discharge current and thrust were measured; specific impulses and thrust efficiencies were evaluated. The plasma potential, channel wall potential, electron temperature and electron number density were measured with an electrostatic single probe. The process of ion generation and acceleration in a Hall thruster was discussed with measured results. The thrust performances were affected by nature of the channel walls. Measured plasma characteristics suggested that the channel wall material affected an ionization region and ion wall losses in the channel, resulting from secondary electron emission. The difference of discharge current between channel materials was considered to be caused by the difference of current density near the inner channel wall.

In magneto-plasma-dynamic (MPD) arcjet generators, plasma is accelerated by electromagnetic body forces. Two types of MPD arcjet generator were developed for applications to mullite, zirconia, titanium nitride and silicon nitride sprayings. The MPD spray process could successfully form dense, uniform and hard ceramic coatings. In titanium nitride reactive spraying, plasma diagnostic measurement and flowfield calculation were also carried out. A large amount of N and N+ was expected to be exhausted with a high velocity from the MPD generator. Both the electron temperature and the electron number density were kept high at a substrate position compared with those for conventional low-pressure thermal sprayings. A chemically active plasma with excited particles of N+, Ti, Ti+ and Ti2+ was considered to contribute to better titanium nitride coatings. All coating characteristics showed that the MPD arcjet generators had high potentials for ceramic spraying. © 2005 Elsevier B.V. All rights reserved.

In a laser ablative thruster, laser is irradiated to some solid propellant it is ablated, and then produced small powders and/or gas particles with high energy are expanded resulting in thrust generation. In this study, a Q-switch Nd:YAG laser with a wavelength of 1064 nm and an output energy of 0.65 J was irradiated to polymer propellants to examine performance characteristics of laser ablative thrusters for small satellites. Impulse bit and mass loss were measured. As polymer propellants, PTFE, PTFE(carbon: 10mass%), PTFE(carbon: 15mass%), POM, POM(carbon: 20mass%), PE and PVC were selected. The performance characteristics mainly depended on specific weight and carbon concentration of polymer propellant. PTFE(carbon: 10mass%) and POM(carbon: 20mass%) were preferable propellants for high performance although with PTFE(carbon: 10mass%) laser should be irradiated to its new surface for every shot. In laser irradiation with PTFE divergent nozzles, there existed an optimum nozzle geometry for improvement of performance characteristics. In a case with a nozzle half angle of 15 deg and a length of 3 mm, the momentum coupling coefficient and the specific impulse reached 112 μNs/J and 300 sec, respectively. © 2006 American Institute of Physics.

In our previous study, it was proved that diamonds could be deposited on thermal spray coated substrate without peeling of and break down of the thermal spray coating even in case of combustion flame CVD by cooling substrate surface during deposition. In this study, to develop easy diamond/metal binary coating deposition process, diamond deposition on the as-deposit thermal sprayed Mo coating was carried out. Consequently, even in case of as-deposit Mo coating, diamonds could be deposited and rigid diamond/Mo complex coating could be deposited by additional Mo thermal spraying after diamond deposition. Besides, the complex coating had higher wear resistance in comparison with the normal Mo thermal spray coating.

円形断面放電室をもつホール型イオンエンジンの性能特性が調べられた。また、イオンコレクタ、エネルギーアナライザー、静電ダブルプローブを用いて、プラズマ物理量測定、イオンビーム測定が行われた。さらに小型のエンジンを開発し、性能の変化が比較検討された。その結果、高性能エンジン開発のための設計指針が得られた。 （担当部分：実験研究、全体の取りまとめ）

固体推進剤テフロンを用いた電熱加速型パルスプラズマエンジンの性能向上を目指して、基礎実験用エンジンを開発し作動実験を行った。特に、放電室断面積を大幅に縮小し発生力積の向上を目指した。放電回路のパラメータ、放電室長さ及び初期充電エネルギーの影響が調べられた。次に放電回路改良の後、初期性能評価、10,000ショットの連続作動試験を行った。その結果、多くの性能向上のための指針が得られ、新しいエンジン構造と作動条件が提案された。（担当部分：実験研究、全体の取りまとめ）

電熱加速型パルスプラズマエンジンの非定常内部現象を解明するために、数値シミュレーションが行われた。パルスプラズマエンジンの性能は放電回路の特性に大きく影響されるため、本計算モデルには放電回路も含まれる。本計算は主に、放電回路、プラズマ流、固体推進剤への熱供給、固体燃料内部の熱伝導の計算で構成され、放電回路はプラズマ抵抗を考慮したLCR直列回路として扱われた。計算結果は実験結果と比較検討され、定量的な一致をみた。（担当部分：数値計算、全体の取りまとめ）

外部磁場をもつパルス作動型電磁プラズマ加速アークジェットエンジンの性能とプラズマ状態が研究された。特に、放電室上流部にカスプ形状の磁場を印加し、推進剤ガスの電離・加熱を促進させることを考えた。さらに２つの外部磁場コイルを利用してカスプ磁場とダイバージェントノズル磁場を同時に印加することも試みた。その結果、放電電圧の上昇を抑え推力のみを増加させることができた。カスプ磁場に起因するホール電流による加熱、ダイバージェントノズル状磁場に起因するスワール加速の効果が推測された。（担当部分：主な実験研究）

ホール型エンジンの推力とプラズマに与えるチャネル壁の影響。(担当部分：作動実験、取りまとめ)

複数の単結晶シリコン棒と電磁加速窒素プラズマを用いて窒化珪素の成膜を行った。放電電流の増加と共に皮膜の厚さとビッカース硬度は大きくなった。また、基板温度の低下と共にビッカース硬度は小さくなり、皮膜構造は非晶質化する傾向があった。 （担当部分：主な実験研究）

反応性の高い作動ガスを用いた、プラズマジェット気流による基材の表面処理が検討された。チタン基材にNHラジカル密度の高いプラズマ流を照射したところ、表面組成分析により窒化チタンが生成されていることがわかった。（担当部分：主な実験研究）

大気溶射皮膜の複合化プロセスの基礎検討として、燃焼火炎ＣＶＤ法によるMo大気溶射基材上へのダイヤモンド合成を試みた。その結果、ダイヤモンドの合成に成功し、Mo皮膜の耐摩耗性と共に硬度上昇が確認できた。（担当部分：実験研究、全体の取りまとめ）

低電力ホール型イオンエンジンにおいて、印加磁場の強度・形状と加速チャンネル長さが性能に及ぼす影響が系統的に調べられた。また噴出プラズマ流の状態とイオンビームの平均エネルギーを計測し、ビーム発散角の算出と電圧利用効率の見積もりを行った。その結果、最適な磁場の強度と形状が明らかになり、更なる性能向上が期待された。（担当部分：主な実験研究）

開放大気下においても成膜可能な熱プラズマＣＶＤ装置の試作、本装置を用いた酸化チタン皮膜の形成、成膜条件の調査、トラバース装置を用いた皮膜の大面積処理の可能性の調査、及び各条件において形成された皮膜の光触媒特性の調査を行った。その結果、非常に安価、かつ高い光触媒特性をもつ酸化チタン膜の成膜に成功した。（担当部分：実験研究、全体の取りまとめ）

電気推進ロケットエンジンの一種である、電熱加速型パルスプラズマエンジンでは、推進剤は固体のテフロンであり、大電流パルス放電によりテフロンが昇華、プラズマ化し加熱され、ノズル膨張し推力を発生させる。繰り返しパルス作動で運転するため、低電力化が可能であり、超小型衛星に適している。本研究では、燃料供給機構をもつパルスプラズマエンジンを開発し、初期性能の測定と連続作動試験を行った。その結果、10-50kg,5-50W超小型衛星搭載用として十分な推進性能が得られた。（担当部分：実験研究、全体の取りまとめ）

宇宙推進用アノードレイヤー型ホール効果プラズマ加速器の基本的な作動特性を取得するために、1 kW級加速器を開発し作動実験を行った。印加磁場強度依存性、放電電圧依存性、作動ガス流量依存性、アノード先端位置依存性及びアノード流路幅依存性が調べられた。その結果、放電電流が最小になり推進効率が最大になる磁場強度が存在することがわかった。（担当部分：実験研究、全体の取りまとめ）

本研究では、宇宙飛翔体表面の絶縁材料上で発生するアーキングの特性、アークスポットの状態を調べるために熱流体計算を行った。得られた結果より、アークスポットの直径は放電前に蓄えられているエネルギーが大きいほど大きくなり、アークスポット近傍では高密度プラズマが生成されていることがわかった。（担当部分：実験研究、全体の取りまとめ）

本研究では、燃焼炎ダイヤモンド合成法における、結晶成長に及ぼす成膜温度の影響が調べられた。その結果、前半の核生成過程は低温環境で行い、後半の結晶成長過程は高温環境で行うのが望ましいことがわかった。（担当部分：実験研究、全体の取りまとめ）

Hirokazu Tahara, Takahisa Masuyama and Koji Horikawa 宇宙環境下における電気絶縁破壊現象の地上シミュレーション実験。(担当部分：作動実験、取りまとめ)

宇宙飛翔体表面の電気絶縁破壊現象の数値計算。(担当部分：数値計算、取りまとめ)

エレクトロダイナミックテザーによる電流捕集の地上実験。(担当部分：作動実験、取りまとめ)

電気推進ロケットエンジンのプラズマ噴流に関する研究。

ホールエンジンの性能とプラズマ状態への加速チャネル材質の影響。(担当部分：作動実験、取りまとめ)

パルスプラズマエンジンの性能測定と流れ場数値計算。(担当部分：作動実験、取りまとめ)

大気圧熱プラズマＣＶＤによる触媒性酸化チタンの高速体積実験。(担当部分：作動実験、取りまとめ)

電磁プラズマジェットを用いた窒化シリコン溶射法の開発。(担当部分：作動実験、取りまとめ)

1kWアノードレイヤー型ホールエンジンの性能向上に関する研究。(担当部分：作動実験、取りまとめ)

円形断面ホール型イオンエンジンの小型化に関する研究。(担当部分：作動実験、取りまとめ)

Yoichi Kagaya and Hirokazu Tahara 磁気ノズルによる電磁プラズマエンジンのスワール加速の研究。(担当部分：作動実験、取りまとめ)

推進剤供給機構型パルスプラズマエンジンの性能測定と数値計算。(担当部分：作動実験、取りまとめ)

大阪大学におけるパルスプラズマエンジンシステムの研究開発。(担当部分：作動実験、取りまとめ)

電磁加速プラズマによる窒化シリコンと炭化シリコン溶射の研究。(担当部分：作動実験、取りまとめ)