Vacuums have been attractive media for researchers and industry to obtain useful plasma, energized particles and current switching effects. These applications require sophisticated control of high voltages or high electric fields, plasma parameters such as density and temperature of charged particles, potential distribution, etc. This article reports current topics on the electrical insulation and plasma application in vacuum.

抄録全体を表示

Output characteristics of a capillary discharge 46.9 nm Ne-like Ar soft X-ray laser pumped by a current pulse (di/dt = 300-460 A/ns, I_max = 15-26 kA) are reported. Using ceramics capillary with an inner diameter of 3 mm and a length of 200 mm or 350 mm, we confirmed a laser spike on the XRD signal. Moreover, using 350 mm capillary, we observed spikes on XRD signals twice in a single shot in particular condition. In classical Young's double slit experiment, using tungsten wire with a diameter of 50 μm or 100 μm, we also confirmed interference fringes of soft X-ray laser which indicate that the wavelength of the laser is about 46.9 nm.

抄録全体を表示

Secondary arc on solar array in space is defined as an arc discharge short-circuiting adjacent solar cells. As operational voltage of spacecraft increases to 100V, there is more risk of secondary arc that can destroy solar array circuit. Secondary arc is categorized as vacuum arc, although its current is very low, even less than 1A. One-dimensional modeling is carried out to derive sets of parameters that satisfy the governing equations. Genetic Algorithm is used to find the optimal set of solutions. Even at a current less than 1A, the solutions exist though the arc voltage is higher than the experimental values by several ten volts.

抄録全体を表示

The improvements of the dielectric materials are one of the most important parts for developing the compact and/or higher power insulators. The breakdown of the rf windows, which pass rf power and isolate vacuum, was induced by the multipactor and surface discharge. Both are related to the secondary electron emission (SEE) and surface charigng. The SEE from alumina materials are measured using a scanning electron microscope (SEM). The single-pulse and multi-pulse methods are applied for the SEE coefficients and surface charging measurements, respectively. The TiN coatings for multipactor suppression are also investigated from the view points of SEE and surface charging. Sapphire shows highest surface charging and has higher SEE coefficients with temperature increase. These results lead to the lower threshold of the electrical breakdown observed for the rf windows. It is confirmed that TiN coatings are effective for the decrease in SEE. The multipulse-measurements indicate TiN coatings lower the surface charging probably caused by the lower SEE.

抄録全体を表示

Novel X-shape filtered arc deposition (X-FAD) apparatus is specially designed and newly developed for thick hydrogen-free tetrahedral amorphous-carbon (ta-C) film coating on superhard alloy (or cemented carbide) substrate. The apparatus has a graphite cathode for deposition of hydrogen-free diamond-like carbon (DLC; ta-C and amorphous carbon: a-C) film and a chromium (Cr) cathode for deposition of Cr layer. The filter duct shapes a composed form of a T-shape filter (T-FAD) for DLC film and a crank-shape filter (Crank FAD) for Cr film. Both carbon plasma beam and Cr plasma beam finally pass through a common plasma duct and scanner part, and go forward to the substrate.
It is known that the adhesion of ta-C film to the superhard alloy is not good and the employment of binding interlayer between ta-C film and superhard alloy is one of the solutions. In this paper, using X-FAD, thick ta-C film was prepared on the superhard alloy. Principal results were as follows. (1) Crank FAD remarkably worked to prepare droplet-free Cr film. (2) Cr single layer did not work as appropriate biding interlayer between superhard alloy and ta-C. (3) Multi interlayer composed of Cr, a-C, and functionally graded DLC (a-C to ta-C), worked as a good biding interlayer for ta-C film on superhard alloy with thickness of more than 1 μm.

抄録全体を表示

Breakdown (BD) characteristics in vacuum are strongly dependent on the electrode surface condition, like the surface roughness etc. Therefore, in order to develop a high voltage vacuum circuit breaker, it is important to optimize the surface treatment process. This paper discusses about the effect of precision-surface-treatment of the electrode on breakdown conditioning characteristics under non-uniform electric field in vacuum. Experimental results reveal that the electrode surface treatment affects the conditioning process, especially the BD voltage and the BD field strength at the initial stage of the conditioning.

抄録全体を表示

We have studied charging and flashover characteristics of a glass insulator with 0.3 - 50 mm long under DC voltage excitation in vacuum. We conducted flashover tests, charge measurements and calculation of surface charge distribution. The insulator was borosilicate, and was in the shape of a right cylinder. The side surface of the specimen was polished to have an average roughness of sub microns or roughened up to several microns. The charging characteristics of insulators were investigated by using an electrostatic probe, which was embedded in the plane cathode and allowed a time resolved measurement of the charging process. As a result, we have confirmed that roughening the surface mitigates the surface charging and thus improves the insulation strength for a specimen up to 50 mm in length. These results are useful not only for high voltage VCB's but also for other equipment that uses high voltage in vacuum such as particle accelerators.

抄録全体を表示

This paper describes vacuum electrical breakdown characteristics for electrodes with spark conditioning process. Two pairs of electrodes processed by spark conditioning were prepared. The conditioning procedure was 500 times repetitive breakdowns by applying positive impulse voltage under ultra-high vacuum condition. Using these processed electrodes, two vacuum gaps were made up by pairing of electrodes used as cathode in spark conditioning process and as anode, respectively. 50 times repetitive breakdown tests were carried out using cathode vs. cathode pair and anode vs. anode pair. As a result, for a pair of cathode vs. cathode, the first breakdown field kept high breakdown field which was almost the same value for the achieved breakdown field by 500 times repetitive spark conditioning. On the other hand, for anode vs. anode pair the first field was much less than that for cathode vs. cathode pair. This is due to the difference of the surface condition between anode and cathode surfaces that were formed by spark conditioning. According to SEM images for anode and cathode after spark conditioning, the profiles had quit difference between anode and cathode surface.

抄録全体を表示

A conventional lecture on Laser Engineering had been done in a lecture room till 1999. A content using on-demand streaming method was made for an online lecture of Laser Engineering in 2000. The figures and equations used on the conventional lecture and the voice recorded for the online lecture were converted to the real media. Then an online lecture has been provided to students by using a Helix Universal Server. The trial of the online lecture was done only for the students who wanted to take the online lecture course in 2000. The online lectures have been recognized as the credits for graduation by the change of a law since 2001. About 100 students have registered the online lecture of Laser Engineering every year since 2001. Here, three years' questionnaire surveys of the online lecture are summarized, and results of examinations on the conventional lecture for two years and on the online lecture for three years are compared. It is recognized for the lecture of Laser Engineering that the educational effect of the online lecture is comparable to or better than that of the conventional lecture.

抄録全体を表示

Since electrical discharge development is very fast and influenced by the probability largely, strict condition control and high-resolution measurements are difficult. This paper describes numerical estimation of the sparkover voltages and time lag (V-t) characteristics utilizing a hydrodynamic numerical numerical modeling of a streamer and the equal-area criterion. V-t characteristics for a step voltage, a steep-front square voltage with a rise time of 20 ns, and 1.8/450 μs impulse voltage are successfully estimated using a single equal-area parameter obtained from the numerical modeling of the streamer. This suggests that a numerical estimation of V-t characteristics for any kinds of voltage wave form may be possible.

抄録全体を表示

This paper describes a suitable driving circuit for micro-plasma sources utilizing the minute gas flow DC discharge. The generator must be provided with a circuit supplying primitive breakdown voltage and one supplying voltage to sustain discharge to obtain an efficient plasma apparatus. Three circuits sustaining discharge are proposed. One regulates DC voltage, another supplies pulse voltage and the other regulates resistance connected with a discharge gap in series. Characteristics of gas flow discharge with helium by supplying DC and DC pulse voltage between a tiny tubular electrode and a metal cathode are examined. The results show that the way supplying pulse voltage has merits which are generating plasma with higher peak energy and obtaining wider plasma energy range compared with the one supplying DC voltage. The paper shows that a circuit supplying pulse voltage is more efficient than one regulating resistance and is smaller than one regulating DC voltage, also.

抄録全体を表示

High-adhesion diamond-like carbon (DLC) film was prepared by a hybrid process of plasma-based ion implantation and deposition using superimposed RF and high-voltage pulses. The adhesion strength of DLC film on a stainless steel (SUS304) was enhanced by the carbon ion implantation to the substrate. Furthermore, ion implantation of mixed carbon and silicon led to considerable enhancement of adhesion strength above the resin glue strength. The adhesion strength of DLC film on the aluminum alloy (A-5052) was improved above the resin glue strength only by the carbon ion implantation to the substrate.

抄録全体を表示

Experiments on microwave plasma generation and its application to microwave beamed energy propulsion were conducted using a 1MW-class, 170GHz gyrotron. The microwave beam was focused using a parabola reflector and plasma was initiated near the focal point in the ambient air. Plasma propagated upstream in the microwave beam channel while absorbing microwave. Its propagation velocity was supersonic when the microwave power density was larger than 75kW/cm². The propulsive impulse was measured using a cone-cylinder shaped thruster model. As a result, maximum momentum coupling coefficient was obtained at a certain plasma propagation distance. In addition, large momentum coupling coefficient was obtained when plasma was propagated at a supersonic velocity. It would be because supersonic plasma propagation forms a strong shock wave, resulting in an efficient pressure increase.

抄録全体を表示

The adhesion of bubbles inside polymer tubes for liquid infusion is a problem leading to inconsistency of the amount of liquid infused. We treated the inside of a polymer tube with atmospheric pressure plasma to create the hydrophilic property and actually attempted to verify the adhesion restraint of bubbles. When the flow velocity was changed to 0.008-0.35m/s, the adhesion of bubbles was observed in all cases using the untreated tube. On the other hand, the adhesion of bubbles was not observed at 0.03m/s or more in the plasma-treated tube. By the plasma treatment, the contact angle of a bubble changed to 61° from 107° in the PVC tube. The change corresponds to 0.26 times decrease in the work to be generated as the bubbles adhere, and it corresponds to 15 times increase in the force to push the bubbles.

抄録全体を表示

To investigate the mechanism of the polarization fatigue of ferroelectric thin films, we analyzed the relationship between the crystalline defects of electrode/ferroelectric interface and fatigue characteristics of PZT thin films. Pt/PZT/Pt thin films were prepared by the chemical solution deposition method, and conditions of Pt/PZT interface were analyzed by TEM-EDX analysis, thermally stimulated current methods and I-V Properties. The PZT layers of about 30nm near the top Pt electrodes became an n-type due to the oxygen vacancies and they formed the contact similar to the top electrode of Pt/n-type PZT/p-type PZT. Because the height and width of the Schottky barrier in the Pt/PZT interface had reduced with the increase of the fatigue, this band structure was observed in the electric field where the Fowler-Nordheim currents were lower than usual. This is considered to be caused by the increase of crystalline defects near the interface due to the impressing of the bipolar pulse. This phenomenon was observed quantitatively by TSC analysis, and the TSC peak of 490K became larger with the increase of the fatigue. The activation energy of the TSC peak was 0.8ev and the defect density was 2.5×10¹⁹/cm³, which is consider to be produced by Pb defects.

抄録全体を表示

Etching characteristic LiNbO₃ single crystal has been investigated using plasma RIE (Reactive Ion Etching) with mixture gases of CF₄/Ar, CF₄/H₂, CF₄/Ar/H₂. The etched surface was evaluated by means of atomic force microscopy. The etched rate for -Z surface of LiNbO₃ single crystal was higher than +Z surface using CF₄/Ar and CF₄/H₂ mixture gases. Possibility of the deep etching at the boundary between -Z surface and +Z surface for partially polarization-reversed LiNbO₃ without mask was investigated. The best condition of the deep etching was obtained by using CF₄/H₂ mixture gas. The value of aspect ratio is approximately 1.0 on this condition.

抄録全体を表示

This paper examines the possibility of a parallel drive at the large amplitude with two ceramic oscillators which have the characteristic difference, and clarifies the relation between an approval process of the parallel drive and a nonlinear phenomenon from the experiment and the proposal locus model. First, it indicates the calculation and the experiment value of the nonlinear resonance characteristic curves of an experimental ceramic oscillator. Next, from the parallel driving experiment at the large amplitude, it is observed that the each oscillator has a peculiar mechanical vibration and confirmed that the parallel drive is build by the drawing effect. Based on these examinations, the building-up locus model when driving in parallel is proposed. As a result of the examination of these experiment and proposal model, the building-up locus which arrive at the parallel operation point are shown and the generation factor of the drawing effect is specified. From this model, it is possible to clarify the building-up characteristic of each element when driving in parallel.

抄録全体を表示

We studied Tb-Fe-Co giant magnetostrictive thin films and researched sputtering conditions to improve their magnetostrictive properties and investigated the possibility of their practical use. The sputtering Ar gas pressure influenced their inner stress and played a very important role for the determination of the magnetic easy axis. The largest magnetostriction was obtained when the Ar gas pressure was set at 0.7 Pa and the inner stress was controlled at an about 50 MPa tensile stress. In the Tb-Fe system, the Curie temperature is very low (about 140°C) compared with bulk materials, but the Curie temperature can be improved with increasing Co ratio. For films over 70% Co ratio, the Curie temperature was more than 250°C and the largest magnetostriction 1508 ppm was obtained at 80.1 % Co ratio. At almost all Tb-Fe-Co thin films, the values of magnetostriction were very high (over 1000 ppm), and the coercive forces were low (around 8 kA/m). Therefore, the Tb-Fe-Co giant magnetostrictive thin films are very appropriate materials for the applications in micro actuators and sensors.

抄録全体を表示

A new method of a water treatment utilizing radicals produced by the discharge on the surface of a gas-layer in water is proposed. Radicals with short lifetime (e.g. OH radical and atomic oxygen) are used effectively for the water purification because radicals contact with water directly. The gas-layer (like a bubble) is formed when the gas is supplied to the reactor. The supply gas was argon. The indigo carmine solution was decolorized using the discharge on the surface of a gas-layer in water. The energy consumption of 1-pulse evaluated from waveforms of the applied voltage and the circuit current. When the total energy consumption was 5.46Wh, the decolorization rate of the indigo solution was 98.0%. The TOC concentration of the indigo solution which performed the discharge process was measured. When the charging voltage was 48.8kV, the treatment efficiency of TOC was 0.174g/kWh.

抄録全体を表示

The present paper concerns the evaluations of the long period super-hydrophilicity of titanium oxide films fabricated by plasma thermal spraying on the aluminum substrate. The fabricated titanium oxide and tungsten doped titanium oxide kept super-hydrophilic surface over 315 days without UV ray illumination. Especially, tungsten doped titanium oxide kept super-hydrophilic surface including the area without dropping of water for 315 days.

抄録全体を表示

Bow-tie tree (BTT) generated from contaminant, e.g., metal, carbon, amber(over cured resin) or void in insulator is a significant deterioration factor of XLPE power cable. However, essential role of water in generation and progress of BTT is not yet sufficiently cleared. In order to investigate the role of water we paid attention to difference in chemical properties of light water (H₂O) and heavy water (D₂O), moreover we evaluated influence of isotopic effect due to hydrogen and deuterium on behavior of BTT generation. In accelerated aging test the number of BTT in XLPE sample, in which copper powder of 500ppm was contaminated as BTT cores, dipped in heavy water (D₂O:100wt%) decreased to one third compared with light water(D₂O:0wt%). Furthermore, the maximum length of BTT decreased with increase in concentration of heavy water. The experimental results show that heavy water exerted a depression effect on generation and progress of BTT. We considered that the depression effect due to hydrogen isotope appeared by inhibiting ionization and elution of BTT cores, because salt-solubility and ionic mobility of heavy water are about 15 to 20% smaller than those of light water. Therefore, the essential role of water seemed to be production and transport of ions in XLPE.

抄録全体を表示