田原 弘一

An electron cyclotron resonance (ECR) plasma source with permanent magnets was investigated for plasma-enhanced chemical vapor deposition of amorphous carbon. By using a mixture of CH4, O2 and H2 gases, this plasma source was used to successfully deposit amorphous carbon at a low pressure (2.7 Pa) and a low substrate temperature (500-600°C). At a 7.7 vol% CH4 concentration and 0.6 vol% O2 concentration, microcrystalline amorphous carbon with crystallites about 0.6 µm in diameter was deposited. Raman spectroscopic analysis showed that this deposit was diamond-like carbon. On increasing the O2 concentration slightly, the size of the deposit decreased. On the other hand, a slight decrease of O2 concentration changed the deposit to graphitic carbon. These deposition characteristics were explained by plasma diagnoses using optical emission spectroscopy and actinometry.

超音速プラズマジェット発生装置の内部のプラズマ状態を調べ、チタン材の窒化を試みた。作動ガスに窒素を用いて照射した結果、チタン材は比較的に低温度で窒化がなされた。測定したプラズマ特性より、極度の温度非平衡状態、化学非平衡状態であり、窒化反応に優位に働いていることが推測された。（担当部分：主な実験研究）

Spectroscopic measurement was carried out to understand the plasma features in a 10-km-class water-cooled direct-current arcjet generator with a supersonic expansion nozzle. Ammonia or a mixture of nitrogen and hydrogen was used as the working gas. In the mixture of N-2+nH(2), the H-2 mole fraction n was varied from 0.5-3.0, in which a H-2 mole fraction of 3.0 corresponded to that of simulated ammonia. The discharge voltage and the vacuum tank pressure for N-2+3H(2) were higher than those for NH3 at a constant discharge current and a constant input power, respectively. These characteristics agreed with those of H-atom electronic excitation temperatures in the constrictor of the nozzle throat. The NH3 and N-2+3H(2) plasmas in the constrictor were expected to be nearly in a temperature-equilibrium condition. On the other hand, the plasmas in the expansion nozzle were in thermodynamical nonequilibrium state because the electron number densities rapidly decreased downstream. As a result, the H-atom excitation temperature and the N-2 rotational excitation temperature decreased from 7000-11000 K in the constrictor to about 4000 g and to 1000-1500 K, respectively, on the nozzle exit with mass flow rates of 0.1-0.2 g/s at input powers of 7-12 kW, although the NH rotational excitation temperature did not show a significant axial decrease.

酸素及び窒素イオン照射による宇宙用高分子材料の分光透過率の変化が調べられた。イオン照射により高分子材料表面の化学構造が変化し、イオン照射量の増大と共に分光透過率が低下していくことがわかった。この結果より、宇宙用熱制御材料としての性能が低下していくことが危惧された。（担当部分：主な実験研究）

大面積・高硬度膜の高速成膜法として、電磁加速プラズマを用いたプラズマ溶射法が提案され、その可能性を明らかにするためにセラミックス溶射が行われた。半径5 cm以上、ビッカース硬度1000以上の大面積・高硬度セラミックスの製作に成功し、反応性溶射への適用も期待された。（担当部分：主な実験研究）

長い陽極と陰極をもつ構造、すなわちチャンネル構造の準定常ＭＰＤアークジェット発生装置を用いて、基礎的な電磁加速過程が研究された。放電室内部の電流分布、電子温度・電子数密度の軸方向分布が測定され、それらは1次元電磁流体モデルを用いた解析結果と比較検討された。作動ガスの種類により、プラズマ生成、加速過程が大きく異なることがわかった。（担当部分：実験研究、全体の取りまとめ）

A quasisteady magnetoplasmadynamic (MPD) arcjet with an applied magnetic field was investigated to improve the thruster performance and understand the complex acceleration mechanisms with both the self-induced and applied magnetic fields. The MPD arcjet was operated with hydrogen, a mixture of nitrogen and hydrogen simulating hydrazine, and argon at discharge currents of 3-18 kA in high specific impulse levels around a critical discharge current predicted from the rules of Alfven's ionization velocity or minimum input power. The application of axial magnetic fields achieved higher thrust efficiencies than those for only the self-induced magnetic field at constant specific impulses, and still achieved stable operations at higher specific impulses with less electrode erosion. The following guidelines were suggested to achieve higher thruster performance: 1) the axial magnetic field strength must be smaller than the azimuthal self-field strength in the main discharge region near the cathode tip, and 2) the applied magnetic field Lines must expand gradually downstream for smooth expansion of plasma. Furthermore, the measured pressures on the electrodes and the current distributions in, the discharge chamber showed that the overall thrust measured by a pendulum method increased, in spite of a decrease in the electromagnetic pumping thrust and a small contribution of Hall acceleration. Thus, an additional thrust component because of the axial magnetic field, such as that caused by swirl acceleration, is expected to exist.

With an increase in the use of polyimides in aerospace applications, the degradation of polyimides caused in the space environment is receiving more attention. In this paper, a ground experiment in which polyimides were exposed to high-energy ions in the space plasma environment was carried out. The effects of oxygen or nitrogen ion bombardment on the chemical structure of polyimide films were investigated by X-ray photoelectron spectroscopy (XPS). The polyimides were exposed to ion beams with energies in the range of 0.5-1.0 keV and in doses between 1.7 x 10(15) and 8.2 x 10(16) ions/cm(2). An in-situ XPS analysis was also carried out, and showed that the ion bombardment changed the chemical structure of the polyimides due to the addition of oxygen and nitrogen ions and the desorption of other components.

A ground facility was developed for simulation of material and reactive space plasma interaction in LEO and for study of spacecraft charging and discharge phenomena. The space plasma simulator consisted of a vacuum tank 0.7m in diameter x 1.5m long, two turbo-molecular pumps with pumping speeds 5 and 3m(3)/s, respectively, achieving some 10(-4)Pa, and an electron cyclotron resonance (ECR) plasma source of a magnetic-field-expansion plasma accelerator. Microwaves of maximum 500 W and 2.45 GHZ were introduced into the discharge chamber of the plasma accelerator, and plasma generated by ECR heating was accelerated through a divergent magnetic field. The sample holder was located in oxygen or nitrogen plasma flows in the simulator. As a result, a clean low-pressure reactive-plasma environment could be produced with the plasma simulator. Plasma properties of plasma density, electron temperature, ion incident energy, ion freestream velocity and atomic oxygen flux were measured. The incident ion energy could be controlled by changing the sample holder potential. The ion freestream velocities for both gases had small variations for the sample holder potential. The flux of ions or atomic oxygens was large enough to simulate plasma environments around spacecrafts on ground for a shorter period than that in practical use in space. The simulator was found to have a high potential for ground material tests.

プラズマジェット発生装置を極度に低圧環境下で作動させ、材料加工へ適用した。作動ガスに窒素ガスを用い、チタン材の反応性成膜による窒化チタンの作成に成功した。本方法は大面積高速成膜へ応用できることが期待された。（担当部分：実験研究、全体の取りまとめ）

超音速プラズマジェット発生装置の内部のプラズマ状態が調べられた。作動ガスには窒素と水素の混合ガスが用いられた。プラズマ放射光が分光器に取り入れられ、分子スペクトル、分子イオンスペクトル、原子スペクトルから分子の振動励起温度・回転励起温度、原子励起特性温度が見積もられ、それら温度が放電室内部では大きく異なっていることがわかった。（担当部分：主な実験研究）

地球低高度軌道（高度：200-1000 km）を飛翔する宇宙飛翔体には、速度7.8 km/sで空気プラズマが衝突している。本研究では、この宇宙飛翔体環境を地上で模擬するために、宇宙プラズマ環境シミュレータを開発した。本装置は大型ソレノイドコイルと電子サイクロトロン共鳴放電型プラズマ源からなる。本研究では、基本作動特性が測定され、シミュレータとして十分な性能を有していることが明らかになった。（担当部分：主な実験研究）

電子サイクロトロン宇宙プラズマシミュレータの開発と性能測定。(担当部分：作動実験、取りまとめ)

電磁プラズマ加速アークジェット陰極近傍のプラズマ状態の研究。(担当部分：作動実験、取りまとめ)

水素・窒混合ガスプラズマジェット流れ場の分光計測と数値計算。(担当部分：作動実験、取りまとめ)

The influence of high-energy charged-particle bombardment and UV light irradiation on chemical structure of polyimide films was investigated to clarify the mechanism of material degradation in space. The films were exposed to oxygen or nitrogen ion beams with 0.5 keV, to electron beams with 20-30 keV and to UV and visible light of 250-600 nm. X-ray photoelectron spectroscopic analysis showed structural changes of the exposed polymers, The optical properties of transmittance and reflectance were also found to be degraded.

Spectroscopic measurements were carried out to understand the are structure and the flowfield in a 10-kW-class water-cooled direct-current nitrogen arcjet engine with a supersonic expansion nozzle for material processing, In the expansion nozzle, the pressure and electron density drastically decreased downstream, and therefore the plasma was in thermodynamical nonequilibrium, although the plasma in the constrictor was expected to be nearly in a temperature-equilibrium condition. The radial profiles of the physical properties for N-2 and N-2(+) showed that there existed a fore flow with high vibrational and rotational temperatures and large electron number densities on the center axis, even at the nozzle exit. Both of these temperatures on the arcjet axis at the nozzle exit and the electron temperature in the constrictor increased linearly with the input power, regardless of mass flow rate, The vibrational temperature ranged from 6000 to 10000 K in input power levels of 5-11 kW and the rotational temperature from 500 to 2000 K.

A long electron cyclotron resonance (ECR) plasma source using slot antennas and permanent magnets was developed for large-area plasma processing. Microwaves were radiated from the slot antennas on a 30-cm-long rectangular waveguide and efficiently absorbed to plasma by ECR magnetic fields of permanent magnets. The plasma source operated above 0.014 Pa for Ar at 437 W. The maximum plasma density was 1.77 ×1017 m-3 at 437 W for 0.078 Pa. The spatial plasma uniformity was ±8.2% within 200 mm length at 437 W for 0.078 Pa. The plasma source was experimentally applied to reactive sputter deposition of TiN film using a mixture of Ar and N2. Titanium nitride film was successfully deposited with ±14.1% spatial uniformity within 160 mm length. From X-ray photoelectron spectroscopic analysis, Ti–N bonds were newly created and the atomic composition ratio was nearly equal to the stoichiometric value of TiN at a N2/Ar mass flow rate of 1.5.

宇宙プラズマ模擬実験装置の開発とそのプラズマ・材料の干渉実験。(担当部分：作動実験、取りまとめ)

To understand degradation of materials due to ion bombardment in a space plasma environment, polymers of polyimide, polyetheretherketone and perfluoroalkoxy, and glasses coated with MgF2 were exposed to ion beams of oxygen and nitrogen with energy levels ranging from 600 eV to 5 keV. For the polymers, x-ray photoelectron spectroscopic analysis showed that the addition reaction of oxygen or nitrogen atoms or the disruption or separation of various structural compounds occurred depending on ion energy and dose. For the glass plate, the coating layer of MgF2 was drastically sputtered. (C) 1995 American Institute of Physics.

Medium-pressure CH4/H-2 plasmas were generated in a discharge tube on the axis of a cylindrical 2.45-GHz-microwave TM(011)-mode-resonance cavity for chemical vapor deposition of diamondlike carbon films. Diamondlike carbon synthesis, plasma diagnostic measurements and kinetic model analyses were conducted to examine the correlation between plasma properties and him features. The characteristics of the calculated H-atom density of the excitation quantum level 4 agreed with those of the measured spectral intensity of the H beta line. Consequently, high density ratios of C atoms to H atoms were required for deposition of diamondlike carbon. On the other hand, the density ratio of CH3 radicals to H atoms was considered to be closely related to the hardness of deposited diamondlike carbons.