田原 弘一

This chapter reveals that in magneto-plasma-dynamic (MPD) arc jet generators, plasma is accelerated by electromagnetic body forces. Two types of MPD arc jet generator are 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 flow field calculation are also carried out. A large amount of N and N+ is expected to be exhausted with a high velocity from the MPD generator. Both the electron and the electron number density are kept high at a substrate position compared with those for conventional low-pressure thermal sprayings. Chemically active plasma with excited particles of N+, Ti, Ti+ and Ti 2+ was considered to contribute to better titanium nitride coatings. The coating characteristics showed that the MPD arc jet generator had high potentials for material spraying. © 2005 Elsevier Ltd. All rights reserved.

Nitriding of metals and reactive spraying for nitride ceramics are planned using a 10-kW-class direct-current nitrogen or H2/N 2-mixture arc plasma jet generator with a supersonic expansion nozzle in a low pressure environment. The H-atom electronic excitation temperature and the N2 molecule-rotational excitation temperature intensively decreased downstream in the nozzle although the NH molecule-rotational excitation temperature did not show an axial decrease. As approaching the titanium plate for nitriding, the thermodynamical nonequilibrium plasma came to be a temperature-equilibrium one. Both the electron number density near the plate and the heat flux into the plate increased with H2 mole fraction for mixtures gases. In cases with H2/N2-mixtures, a radical of NH with a radially wide distribution is considered to contribute to the better nitriding as a chemically active and non heating process. Numerical simulation was carried out to examine interactions between injected ceramic particles and the nitrogen plasma flow. When plasma was accelerated to supersonic flow through the nozzle, ceramic particles were smoothly accelerated by the aerodynamic drag force and heated in the highly-reactive plasma flow. The calculated results showed that the supersonic plasma jet in thennodynamical and chemical nonequilibrium state might have some potentials for material processing, even for spraying, because of its high reactivity.

Carbon nitride films were deposited by reactive sputtering process and by pulsed laser ablation process with substrate bias. The atomic composition ratio of N/C and sp³ bonding ratio increased with substrate bias voltage up to 100 V. The maximum atomic composition ratio of N/C was 0.35 for reactive sputtering and 0.24 for laser ablation. However, the hardness of the films is high for reactive sputtering, and low for pulsed laser ablation. From the FE-SEM and TEM observation, the morphology of the films had dense structure by reactive sputtering and nano-size columnar structure with uneven surface by pulsed laser ablation.

In this study, diamond deposition on traversing substrate was carried out in order to get useful information for utilizing combustion flame method. In the case of stationary substrate, diamond particles were obtained on the condition that C2H2/O-2 flow ratio was from 1.00 to 1.15, while no particles could be obtained in oxygen rich environment. However, in the case of traversing substrate, dense diamond belt was deposited without oxidizing of the diamond particles due to oxidative flame. From these results, it was proved that large area deposition by substrate traversing was available even in the case of combustion flame CVD. (C) 2003 Elsevier B.V. All rights reserved.

Spectroscopic and electrostatic probe measurements were made to examine plasma characteristics under nitriding for a 10-kW-class direct-current arc plasma jet generator with a supersonic expansion nozzle in a low pressure environment. Heat fluxes into the plate from the plasma were also evaluated. Ammonia and mixtures of nitrogen and hydrogen were used as a working gas. The H-atom electronic excitation temperature and the N(2) molecule-rotational excitation temperature intensively decreased downstream in the nozzle although the NH molecule-rotational excitation temperature did not show an axial decrease. As approaching the titanium plate, the thermodynamical non-equilibrium plasma came to be a temperature-equilibrium one. Both the electron number density near the plate and the heat flux increased with H(2) mole fraction for mixtures gases. In cases with mixtures of N(2) and H(2), a radical of NH with a radially wide distribution was considered to contribute to the better nitriding as a chemically active and non-heating process. (C) 2003 Elsevier B.V. All rights reserved.

In order to develop an easy and rapid elements-doped diamond film synthesis process, as a basic study, rapid diamond film deposition using combustion flame CVD and nitriding of the diamonds using supersonic expanding nitrogen plasma jets were carried out. The supersonic expanding plasma jets can be used as low-temperature plasma jets with high chemical reactivity due to supersonic adiabatic expansion and frozen flow. Actually, nitriding of titanium, steel and aluminum using these plasma jets were successfully carried out in our previous study. Consequently, by varying deposition conditions during diamond deposition, diamond particles could be deposited densely during only 20 min of deposition though it was difficult to deposit diamond particles densely under constant deposition conditions. Besides, though no nitride was produced in the case of pure nitrogen plasma jets, the color of diamonds varied from transparent to black during the operation and carbon nitride could be investigated in the plasma jets-irradiated diamonds using XRD in the case of hydrogen/nitrogen plasma jets. From these results, using hydrogen/nitrogen mixture plasma jets, nitrogen-doped diamonds could be produced by means of these techniques and the process was found to have high potential for elements-doped diamond synthesis. (C) 2004 Elsevier Ltd. All rights reserved.

高度な宇宙飛翔体の運用において、導電性の「ひも」（テザー）を宇宙空間に伸展させ電子を収集することが必要である。本研究では、導電性テザーの作動特性の取得、および数値計算による電子収集過程の解明と収集電流値の見積もりが行われた。プラズマ粒子法を用いた数値計算より、テザー前面には無衝突衝撃波が形成され、それにトラップされたイオンに引き付けられた電子がテザーに収集されることがわかった。見積もられた電流値は理論最大電流値とほぼ一致した。（担当部分：主な実験研究）

汎用の電子放出機器として使用されているホローカソードは、宇宙用機器としても有用である。本研究では、プラズマ中でのホローカソードの電子放出特性が調べられた。長時間運転、耐久作動試験と共に数値計算による電流見積りが行われた。ホローカソードの作動特性には、拡散作動モードとスポット作動モードの2つがあり、後者の作動の場合放出電子電流が大きく宇宙における安定作動に有益であることがわかった。（担当部分：主な実験研究）

電磁加速プラズマジェットを利用した材料溶射が研究された。各種の金属パウダー、セラミックスパウダーの導入による厚膜溶射、金属パウダーと各種の作動ガスプラズマとの化学反応による反応性厚膜溶射が検討され例が示された。

ホール型イオンエンジンのプラズマ生成・イオン加速過程を明らかにし推進性能を予測するために、簡易1次元流れ場の計算モデルが構築された。この計算コードを用いて、既存のホール型エンジンの加速チャンネル長さとその内部の磁束密度の違いによる特性の相違が調べられた。効率よい電離・加速を実現するためには、磁力線をチャンネル出口付近に集中させ、電離と加速をチャンネル出口付近で一気に行わせる磁場構造が望ましいことがわかった。（担当部分：数値計算、全体の取りまとめ）

本研究では、地上模擬実験により、宇宙飛翔体表面の絶縁材料上における放電現象と、周辺プラズマがその放電特性に与える影響が調べられた。陽極酸化アルミニウム表面で発生するアーク放電の特性を測定した結果、アーク電流のピーク値とアーク放電時に流れる全電荷量は初期印加電圧、周辺中性粒子密度の増加とともに大きくなることがわかった。（担当部分：主な実験研究）

棒状の単結晶シリコンと窒素プラズマを用いて、窒化珪素の成膜が行われた。溶射条件を最適化することにより、ビッカース硬度1300以上の高硬度かつ高速成膜に成功した。これまでのPVD法、CVD法を数倍上回る成膜性能が得られた。（担当部分：主な実験研究）

本研究では、HVOF溶射における、投入する溶射粉体の条件、ノズルサイズ、燃焼ガスの条件を入力すれば、直ちに基材直前での粉体の速度・温度が出力される簡易計算コードを開発した。燃焼ガスは等エントロピー圧縮性流体として取り扱い、ノズル内部は準１次元流れ、ノズル外部は２次元不足膨張流れを仮定した。ニッケル・クロム系合金の溶射を計算したところ、その結果はこれまでの溶射結果、経験則とほぼ一致し本計算コードが利用できることがわかった。（担当部分：主な数値計算）

大気熱プラズマＣＶＤ法による光触媒酸化チタン皮膜の実用化を目的として、酸化チタン皮膜へのアモルファス相導入による皮膜の高強度化を図った。その結果、成膜距離を大きくすることにより、皮膜の結晶化度は減少し皮膜中へのアモルファス相の導入が可能であり、皮膜強度も向上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）

外部磁気ノズルをもつ電磁プラズマエンジン噴出流の特性の研究。(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放電室の長さと材質の性能特性への影響。(担当部分：作動実験、取りまとめ)

宇宙プラズマ環境中での宇宙飛翔体の表面放電現象の地上模擬実験。(担当部分：作動実験、取りまとめ)

ホール型イオンエンジン性能に与える加速チャンネル材質の影響。(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イオンエンジンの性能特性の取得。(担当部分：作動実験、取りまとめ)

円形断面をもつ低電力ホール型イオンエンジンの性能特性の取得。(担当部分：作動実験、取りまとめ)

レーザーアブレーションエンジンの性能に及ぼすノズル形状の影響。(担当部分：作動実験、取りまとめ)

低電力アークジェットエンジンの噴出流の状態に関する研究。(担当部分：作動実験、取りまとめ)

宇宙プラズマからのベアテザーの電子収集の地上実験。(担当部分：作動実験、取りまとめ)

ホール型イオンエンジン流れ場の１次元数値計算による性能予測。(担当部分：数値計算、取りまとめ)

低電力ホール型イオンエンジンの磁場と加速チャネルの最適化。(担当部分：作動実験、取りまとめ)

宇宙プラズマ環境下の飛翔体表面上でのアーキング現象の数値計算。(担当部分：数値計算、取りまとめ)

電磁加速プラズマによる窒化シリコン照射に関する研究。(担当部分：作動実験、取りまとめ)

同軸テフロン放電室パルスプラズマエンジンの性能特性の取得。(担当部分：作動実験、取りまとめ)

ホール型イオンエンジンの推力特性とプラズマ加速過程の研究。

直流アークジェットエンジンの噴射プラズマ流の研究。

材料窒化用超音速窒素水素混合ガスプラズマの噴流特性の研究。(担当部分：作動実験、取りまとめ)

Thermal plasma CVD is hoped to be made fit for practical use because this process is the process which can fabricate precisely structure and component controlled coatings. Especially, TPCVD will be used in the industrial fields where thermal spraying has been used so far since TPCVD come to be studied under an atmospheric environment recently. However, TPCVD coatings fabricated under an atmospheric environment is porous and brittle. So that, TPCVD has been mostly carried out under a low pressure environment and high equipment cost has been demanded. As for the method to solve this problem, according to the report on a gas-deposition process, improvement of the jet flow is thought to be useful. Therefore, in this study, in order to obtain dense and rigid film by TPCVD under an atmospheric environment, Dense oxide coating deposition by High velocity TPCVD utilizing boiling of metal alcoxide was carried out. Consequently, though only brittle coating was deposited on the condition without boiling of metal alcoxide, dense and rigid coating was deposited even under an atmospheric environment on the condition with boiling. From this result, TPCVD was found to have high potential for rapid deposition of dense and rigid coatings.

Spectroscopic and electrostatic probe measurements were made to examine plasma characteristics under nitriding for a 10-kW-class direct-current arc plasma jet generator with a supersonic expansion nozzle in a low pressure environment. Heat fluxes into the plate from the plasma were also evaluated. Ammonia and mixtures of nitrogen and hydrogen were used as the working gas. The H-atom electronic excitation temperature and the N-2 molecule-rotational excitation temperature intensively decreased downstream in the nozzle although the NE molecule-rotational excitation temperature did not show an axial decrease. As approaching the titanium plate, the thermodynamical nonequilibrium plasma came to be a temperature-equilibrium one. Both the electron number density near the plate and the heat flux increased with H-2 mole fraction for mixtures gases. In cases with mixtures of N-2 and H-2, a radical of NH with a radially Aide distribution is considered to contribute to the better nitriding as a chemically active and non heating process.

In magneto-plasma-dynamic (MPD) arcjet generators, plasma is accelerated by electromagnetic body forces. The MPD arcjet generator can produce higher-velocity, higher-temperature, higher-density and larger-area plasmas than those of conventional thermal plasma torches. Two types of MPD arcjet generator were developed for applications to ceramic spray coatings. One generator was installed with a cathode covered with mullite or zirconia ceramics and the other with a titanium cathode. The former was operated with Ar for mullite or zirconia coating by an ablation process of the cathode cover and the latter with N-2 for titanium nitride coating by a reactive process between ablated titanium particles and nitrogen plasma. The MPD spray process could successfully form dense, uniform and hard ceramic coatings. In titanium nitride reactive spraying, plasma diagnostic measurement and flowfield analysis 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 expected to contribute to better titanium nitride coatings. All coating characteristics showed that the MPD arcjet generators had high potentials for ceramic spray coatings.

Spectroscopic and electrostatic probe measurements were made to examine plasma characteristics with or without a titanium plate under nitriding for a 10-kW-class. direct-current arc plasma jet generator with a supersonic expansion nozzle in a low-pressure environment. Heat fluxes into the plate from the plasma were also evaluated with a Nickel slug and thermocouple arrangement. Ammonia and mixtures of nitrogen and hydrogen were used as a working gas. The NH3 and N-2+3H(2) plasmas in the nozzle and in the downstream plume without a substrate plate were in thermodynamical nonequilibrium states.. As a result, the H-atom electronic excitation temperature And the N-2 molecule-rotational excitation temperature intensively decreased downstream in the nozzle although the NH molecule-rotational excitation temperature did not show an axial decrease. Each temperature was kept in a small range, in the plume without a substrate plate except,for the NH rotational temperature for NH3 working gas. On the other hand, as approaching the titanium plate, the thermodynamical, nonequilibrium plasma came to be a temperature-equilibrium one because the plasma flow tended to stagnate in front of the plate. The electron temperature had a small radial variation near the plate., Both the electron number density and the heat flux decreased radially outward, and an increase in H-2, Mole fraction raised them at a constant radial position. In cases with NH3 and N-2+3H(2), a radical of NH with a radially wide, distribution was considered to contribute to the better nitriding as a chemically active and non heating process.

マサチューセッツ工科大学（米国）との共同研究として、ホール型イオンエンジンの流れ場の準一次元流体解析が行われた。全体の質量・運動量・エネルギー保存式のほか、電子の運動量保存式とエネルギー保存式が使用された。また熱平衡の電離反応、放電室壁面上の質量・運動量・エネルギー損失の条件が考慮された。計算された結果は実験結果と定性的に一致し、内部の放電状態を十分模擬することができた。（担当部分：主な数値計算）

ホール型イオン推進機の流れ場の準一次元流体解析が行われた。既存のホール推進機と同じ形状と作動条件のもと計算が実行された。計算された推進性能は、放電電流は実験値とほぼ一致したが、推力は異なり、今後は計算モデルの改良が必要である。２次元粒子モデルによる計算コードの開発が提案、議論された。（担当部分：主な数値計算）

超音速プラズマジェットの下流に平板が配置され、その直前のプラズマ状態と平板に流入する熱流束が研究された。作動ガスとしてアンモニアガスと窒素・水素混合ガスが用いられた。平板の有無によって、平板設置位置でのプラズマ状態は大きく異なり、平板がある場合その近傍直前で各種の温度は近づいてくる（緩和方向に向かう）。また熱流束はタンク内圧の影響が大きいが、水素原子、水素を含む活性種の衝突効果も無視できないと推測された。（担当部分：主な実験研究）

基材表面洗浄機能を有する大気熱プラズマＣＶＤ装置の開発を目的として、基材を陽極とした移行性アークを用いた基材へのプラズマ照射、および基材設置型陽極を用いた非移行性アークを用いた基材へのプラズマ照射を行った。その結果、基材設置型陽極を用いた場合基材の表面を溶融させることなく、スパッタリングによる洗浄効果が確認できた。（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の磁場と加速チャネル最適化の研究。(担当部分：作動実験、取りまとめ)