A method to determine the refractive index and thickness of topcoat of thermal barrier coating (TBC) from the reflected waveforms of terahertz waves was developed. The method was applied to specimens of yttria stabilized zirconia (YSZ), which is the topcoat material. The obtained refractive index was in agreement with that obtained by time-domain terahertz spectroscopy in a transmission configuration, and the obtained thickness was in agreement with measurement results using a contact thickness gauge. The method was also applied to a TBC specimen, and the planar distribution of the refractive index and thickness of the topcoat were obtained. The obtained thickness was in agreement with microscope observation of the cross section of the specimen. The results show that reflection measurement of terahertz waves is useful for nondestructive testing of TBC applied to gas turbine blades.

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An accelerated aging test has been carried out to reveal correlations and differences between terahertz imaging and electrochemical impedance measurements in the detection of rust regions in coated steel plates. Intensity distribution measurements of reflected THz waves use the absorption characteristics of rust. Therefore, a good correlation between the THz reflection absorption and the proportion of the rust area relative to the total specimen area has been found. Electrochemical impedance gradually decreases with age, which shows the effectiveness of this measurement technique. A good correlation between values of THz absorption and film impedance indicates the possibility that THz measurements can evaluate the extent of degradation. The observed frequency spectra of the complex impedance are similar to what is observed in dielectric materials containing many charges. This is based on the assumption that impedance measurements affect the water blocking ability of the coating.

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The temperature and magnetic field dependence of 526GHz submillimeter-wave propagation characteristics in surface waveguide utilizing an n-InSb slab as plasma material have been studied experimentally and theoretically. The result of the theoretical analysis indicates that a surface wave resonance occurs and nonreciprocity of more than 27dB/mm appears in the transmission in an applied magnetic field B_s of 0.2 T at 77 K, and that, for temperature above 180 K, B_s increases with increasing temperature. Experimentally observed results are in qualitative agreement with theoretical predictions. These findings indicate the possibility of achieving nonreciprocal devices in a surface waveguide consisting of an n-InSb slab.

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The responsivity of a room-temperature GaAs Schottky barrier diode (SBD) mixer for 2.5 THz has been measured by using 14 far infrared laser lines in the frequency range of 1.6-6.3 THz. The SBD mixer has been detectable up to 6.3 THz. We have succeeded in the detection of two-color beat signals of simultaneously oscillated 5.2- and 6.3-THz CH₃OD lasers by using the SBD mixer. As the application, it has been verified that the SBD mixer has been usable for beat frequency stabilization of the 5.2- and 6.3-THz CH₃OD lasers of a two-color interferometer for fusion plasma diagnostics.

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A new electro-optic (EO) sampling scheme, which we refer to as “heterodyne EO sampling” for detection of pulsed terahertz (THz) waves, is proposed and demonstrated. In this heterodyne EO sampling scheme, the intensity change in the sampling optical pulse induced by a THz field in a nonlinear crystal is measured without using any polarization optics. Applied in conjunction with the non-collinear Cherenkov-phase matching technique, this method allows for efficient and easy detection of pulsed THz wave using a simpler optical setup compared with the conventional EO sampling method.

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The generation of a stable and wide range THz wave using a chaotic oscillation in a multimode semiconductor laser with an optical delayed feedback by the external mirror is investigated. And fiber coupler is also used for easy optical alignment. In this paper, the spectrum of laser chaos is compared with that of the CW steady state oscillation. THz spectrum is limited to 35.2GHz and a THz signal (a current of photoconductive antenna) is not stable using a CW steady state laser. Wide range spectrum of THz wave above 35.2GHz is obtained and a THz signal is also stronger and stable in the case of using a chaotic laser compared with that of using a CW steady state laser.

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The compact Cherenkov free-electron laser operating in the terahertz spectral range is being developed. The analysis of the double-slab type optical resonator clarified the resonant frequency, the small signal gain and the saturation power of the device. One dimensional simulation code predicted a small signal gain of 6% with a 50kV/3.6mA electron beam. Saturation power was estimated to be 90mW. The out-coupling structure of the resonator was designed by using a 3D simulation code. A transmittivity 3.0% and spread angle 0.4rad was predicted.

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To evaluate cavity resonance modes in terahertz-wave oscillators using intrinsic Josephson junction stacks in high-temperature superconductors, an analytical solution of the coupled sine-Gordon equation was obtained by a continuous approximation. For a rectangular stack with a realistic scale, 80μm wide, 300μ m long and 1.1μm (∼700 junctions in the stack) in height, I-V characteristics and field distributions were calculated from the solution. Peak structures were appeared in the I-V curves and corresponded to cavity resonance modes, which were similar to those in a rectangular waveguide cavity. The maximum peak height was obtained at a bias voltage where the TE^y₁₁₁ mode at 0.51 terahertz was excited by the ac Josephson effect. The peak height decreased with increasing a radiation conductance that was introduced for including a radiation loss in the calculation. For design of antenna-coupled oscillators, a junction impedance was also evaluated. These results are useful for future improvement of the oscillators using intrinsic junctions.

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In this study, I experimentally clarified the nature of the characteristics of the electrostatic discharge (ESD) that occurs when a charged object moves toward a stationary grounded object. The spark lengths, discharge currents, and induced voltages in a magnetic probe were measured when a charged metallic spherical electrode connected to a 422 pF capacitor approached a stationary grounded object, which was the current target, for different moving speeds of the charged metallic spherical electrode in the range of 1-100 mm/s. The charge voltages of the capacitor were +6.5 kV and +10 kV. According to the result, the average gap length shortened with the moving speed of the spherical electrode. The average peak values of the discharge current and the induced voltage were likely to increase with the moving speed of the spherical electrode. The average rise times of the discharge current and the induced voltage were likely to reduce with the moving speed of the spherical electrode. The relation between the spark length and the discharge current due to ESD can be explained qualitatively by using an equation derived from the spark resistance formula proposed by Rompe and Weizel.

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Optical absorption spectra and photoluminescence spectra were obtained for eight kinds of polyolefin sheet samples using photons in a range from visible to vacuum ultraviolet. Almost all samples were found to exhibit an absorption peak at around 6.5 eV and a luminescence band at around 4.3 eV. The luminescence was found to be induced by the absorption. Furthermore, it was found that successive absorption of ultraviolet photons weakened the luminescence intensity. It is assumed from these results that α, β-unsaturated carbonyls are luminous and that the carbonyls are decomposed through the Norrish type II reaction by absorbing ultraviolet photons. Quantum chemical calculations were carried out using polyethylene models with and without an unsaturated carbonyl to verify the above-mentioned assumption. As a result, the model with an unsaturated carbonyl was found to have localized electronic states in the forbidden band. One of the differential energies between the states is close to the photon energy, by which the luminescence is induced. The bond length of a double bond, which is next to the carbonyl, was found to be longer at the excited singlet state than at the ground state. These results obtained by computation support the above-mentioned assumption of the luminescence center and its decomposition.

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Complete decomposition of perfluorooctanoic acid (PFOA) at a concentration of 41.4mg/L and perfluorooctane sulfonate (PFOS) at a concentration of 60mg/L in water was successfully demonstrated by DC plasma within oxygen bubbles. PFOA and PFOS were decomposed completely after 3-hour operation and 8-hour operation, respectively. The decomposition efficiency was evaluated by measuring the amounts of fluorine ions which were detached from PFOA or PFOS in the solution. From the measurement of LC/MS, the main by-products generated during the plasma treatment turned out to be perfluorocarboxylic acids. For the practical application, 2-parallel operation of DC plasma was also demonstrated as a basic technology for a large capacity reactor. The decomposition efficiency of 2-parallel operation was at the same level as that of single operation.

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Multi-walled carbon nano-tubes (CNT)/epoxy nano-composites were fabricated and coated onto epoxy insulating substrates in order to uniformize the surface conductivity. The effects of polymer functionalization of CNT were investigated on the dispersion of CNT in an epoxy matrix and the electrical surface conductivity. It was elucidated that grafting polymer molecules onto the CNT surface improve the dispersion of CNT in an epoxy matrix compared to those containing CNT without functionalization. The surface conductivity of nano-composites decreases thanks to uniform dispersion of CNT.

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Polyvinyl chloride (PVC) is the most popular insulating material for electrical wiring instruments. The exothermic reaction at over 150°C may cause deterioration of insulating properties in the PVC. Therefore, it is important to clarify heat degradation in the PVC, not only to investigate ignition of electrical wiring instruments but also to use electric products safely. It is known that ultraviolet ray (UV) irradiation causes PVC chemical deterioration and the conductivity increases.
Generally it has been considered that the electrical breakdown property, electrical conduction and insulating performance are affected by the space charge accumulation in the insulation material. A high temperature pulsed electroacoustic (PEA) system up to 250°C has been developed, and the PEA system can measure the space charge distribution and conduction current in the high temperature, simultaneously. In this paper, the space charge distribution and conduction current have been measured up to electrical breakdown in the non-UV-irradiated sample (normal PVC), 353nm and 253nm UV-irradiated PVC sample in the range from room temperature to 200°C under DC electric field. In the short wavelength UV irradiated (253nm-300hour) PVC sample, the deterioration of breakdown strength at 90 to 150°C, and the negative packet-like charges are observed at 60 to 100°C, the positive charge accumulated in front of both the anode and the cathode over 90°C, and electric field is higher near the cathode side because the amount of positive charge of cathode side is larger.

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Many kinds of insulating materials are used outside a spacecraft. Those are FEP films, polyimide films and so on, and are used as thermal control materials. These materials are exposed to charged particles environment around a spacecraft. So these materials charge up due to the charged particles, especially electrons. It is pointed out that charge-up on these materials is likely to cause discharges on the surfaces. From this viewpoint, we have investigated the charging potential characteristics of 127 μm thick FEP film, typical thermal control material, by irradiating electrons with various energies below 20 keV. In the dependence of the charging potential on the electron energy, we found that the electron energy at which no charge-up occurs is about 2.7 keV. It is thought to be the energy at which secondary electron emission yield becomes one. This indicates that electron irradiation to the FEP film with the energy lower than 2.7 keV induces positive charging. From the charge decay characteristics after electron irradiation the volume resistivity of the film was also obtained as a function of electric fields in the bulk of the FEP film.

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In order to propose a method for producing water trees that measure a few millimeters in length in 20kV class to 60kV class XLPE cables, we discussed defect types and thermal conditions. First, surface roughness, needle protrusions, and line cracks were formed on the XLPE insulation surface of 6.6kV cables, and it was found that the water tree grew to a few millimeters in length from the needle protrusions and the line cracks. Second, water trees were generated in XLPE sheet and cable samples at room temperature and under a heat cycle and continuous elevated temperature conditions. Here, the longest water trees grew at room temperature. From these results, we selected needle protrusions and line cracks as defects and set room temperature as an artificial water tree degradation method. This method was applied with needle protrusions to a 22kV class XLPE cable, and we found that water tree length reached a few millimeters and AC breakdown voltage decreased to approximately 35% of the initial value.

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We describe experimental results and discussions on the decolorization of humate solution by ultraviolet (UV) irradiation. Two kinds of low pressure mercury lamps are prepared as UV source and the shortest wavelength of their light emission are limited at 180 and 200 nm. The absorbance and total carbon concentration in the humate solution is measured by a spectrophotometer and a total organic carbon analyzer. From the results, the temporal variation of absorbance and total carbon concentration in the humate solution is observed after ultraviolet irradiation. It is clarified that the variation of absorbance in the humate solution by UV in shorter than 200nm is remarkable to decolorize the humate solution.

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Radicals produced in an atmospheric DC corona discharge above water are investigated by in-situ infrared absorption spectroscopy. It is found that HO₂ radicals are produced in the corona discharge, and its relative concentration tends to decrease with the increase of the distance from water surface, namely with the decrease of the H₂O concentration.

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Plasma pile-up and ejection of current sheet was measured for the first time by eight channels CO₂ laser interferometer during the impulsive magnetic reconnection in the TS-4 tokamak merging experiment. While reconnection of two merging tokamaks under high guide field is as slow as the Sweet-Parker model, their acceleration by external coils cause fast reconnection with density pile-up and ejection. We modified the Sweet-Parker model to include those two effects and found that its new theoretical inflow velocity agrees well with the measured velocity.

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We provide a simplified measurement method for repetitive partial discharge inception voltage (RPDIV) of enameled wires subjected to repetitive impulses. Previously, a large number of faint discharge signals were monitored on a high-spec digitizing oscilloscope with long memory to count the number of the discharges after the repetitive voltage application was finished. In this paper, a logic pulse produced by a faint discharge light is directly sent from a detector to a personal computer and then it is counted as one partial discharge. Sequence of the impulse voltage repetition is also controlled by the computer, so that statistic data of RPDIV is automatically obtained by using the very simple equipment without the oscilloscope.

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