Dispersion relation of a sinusoidally corrugated wall waveguide employed in backward wave oscillators or traveling wave tubes has been analyzed and easured. The waveguide is designed and fabricated by casted aluminum. It is concluded that microwaves have different characteristics of body-wave and surface-wave in fast and slow wave regions, respectively, with respect to the velocity of light in vacuum.

View full abstract

There are several methods based on the Druyvesteyn's probe theory to measure the electron energy distribution function (EEDF) in the positive column of the glow discharge, for example the second harmonic method (2ω) and the amplitude modulation method (AM). We propose the admittance method (dY) to measure EEDF and compare dY with 2ω and AM.
The calculated electron swarm parameters from measuring EEDF by using dY and 2ω, for example, mean energy of electrons, mean free pass, diffusion coefficient, mobility and drift velocity of electrons, approximately agreed with the parameters which were obtained by solving Boltzmann equation in He glow discharges. The admittance method is superior to other methods to simplify measuring circuits and to increase the accuracy of measurement.

View full abstract

X-ray radiation: bremsstrahlung and characteristic X-ray, in electron beam bombarded X-ray source is numerically analyzed with the Monte Carlo technique. In order to calculate the radiation, scattering processes such as bremsstrahlung, plasmon scattering, elastic collision, inner shell ionization, and secondary electron emmission are taken into account.
The calculated relation between X-ray intensity and electron energy agrees with the experimental results reported by other groups. The intensity of bremsstrahlung has strong dependence on the angle because of absorption. The thickness of a foil target in which the X-ray intensity is maximized is smaller than electron mean range. Back scattered X-ray intensity in conventional X-ray tubes varies as the target angle. The peak of X-ray intensity angular dependence is obtained when the angle is 20°-40°.

View full abstract

The influence of CO on destruction processes of metastable nitrogen molecules N2(A3∑⁺ _u) was investigated in non self-sustaining Townsend discharge region. We observed the transient ionization current after turning off the UV light experimentally, and discussed the destruction processes of metastable molecules N2(A3∑⁺ _u) in N2/CO mixture gases. From the result of our experiments, we confirmed the effect on collisional quenching of N2(A3∑⁺ _u) of CO, but we found that our data did not conform the theortical loss processes due to the diffusion and collisional quenching.
In order to explain these phenomena, we proposed two possible effects due to small amount of CO in N2. One was an increase of the reflection coefficient of N2(A3∑⁺ _u) at the surfaces of electrodes, and the other was an increase of N2(A3∑⁺ _u) flux to the cathode.

View full abstract

Conduction characteristics were studied in a liquid-crystal polymer (LCP), a kind of superengineering plastic with the highest-class thermal resistivity among existing thermoplastic polymers. The investigated all-aromatic polyester type nematic thermotropic LCP showed four thermally stimulated current (TSC) peaks: P_A moving toward a higher temperature till the final temperature 105°C as the biasing temperature increases, P_B around 122°C, P_C around 150°C and P_D around 190°C. Based on the study on the effects of biasing field, biasing time, and the application of collecting field on TSC spectra and the measurement of thermally stimulated surface potential, it is considered that P_A and P_B are respectively due to the depolarization of oriented dipoles and that of ionic spacecharge polarization. The DC conduction current at temperatures above 125°C is substantially affected by ions. For example, a current Beak is observed after the polarity of bias voltage was reversed, indicating the accumulation of ions. The decay of conduction current with time due to the decrease in ion concentration is also observed.

View full abstract

Solubility of copper in insulating oil depends on sulfur contents and component of insulating oil. As increasing of sulfur contents, the solubility of copper becomes large. When being added di-tert-butylparacrezole and benzotriazole into the insulating oil, solubility of copper becomes small. Evolution of combustible gas is proportional to amount of copper in insulating oil, and type of gas pattern due to results of gas analysis in insulating oil depends on chemical component of insulating oil. In the case of low aromatic content oil, hydrocarbon gas evolves preferentially, but in the case of high aromatic content oil, hydrogen gas evolves preferentially. Although degradation of the insulating oil is effected by solution of copper, breakdown voltage of insulating paper is not falling down.

View full abstract

When partial discharge (PD) was measured with the conventional pulse method, it sometimes apparently disappeared. However, it turned out that the PD did not actually disappear, but only became a large number of very small partial discharges known as swarming pulsive microdischarges (SPMD). After this silent stage, detectable PD appeared again, leading to final breakdown. Since SPMD are missed in the conventional PD pulse detection method, it is necessary to pay careful attention to SPMD in terms of insulation diagnosis. We developed a personal-computer-aided partial discharge analyzing system for SPMD measurement. Based on the measurement with this system, a new PD parameter, the SPMD ratio, was introduced for quantitative analysis of SPMD. Using the developed system and the new parameter, partial discharge characteristics of the CIGRE method-II (CM-II) specimen and the modified one were studied to clarify the factors affecting the occurrence of SPMD. It became clear that the composition of the air in void is one of such factors, but it is not a decisive one, because SPMD, onece appeared, continued after the exchange of the gas in the gap with fresh air. Void surface roughness caused by the PD degradation is found to be one of main factors. Further the amplitude and the frequency of the applied voltage also affect the occurrence of SPMD. In the needle shape internal void specimen, SPMD appeared before the tree initiation, suggesting the close relation between the occurrence of SPMD and the PD degradation.

View full abstract

We are developing a new type of superconductor with high elastic modulus fibers for the application of high-field pulsed superconducting magnets, which we call Fiber-Reinforced-Superconductor (FRS). FRS has great potential for the construction of a 15 T-class pulsed magnet with keeping its size equal to ITER because stainless steels of cable-in-conduit-conductors could be largely reduced.
This paper presents a preparation technique of FRS and its measured superconducting characteristics including strain-Ic relation. FRS has a critical current density of 600 (A/mm²/initial niobium) at 15 T, which is almost equal to one of commercial bronze-processed wires. The intrinsic strain vs. I_c characteristics is similar to that of a bronze-processed wire. Thermal strain on FRS are also discussed because materials with high elastic modulus tend to have low thermal contraction which leads to degradation of superconducting characteristics of Nb₃Sn layer. Possibilities are shown to overcome the degradation with keeping very high elastic modulus of tungsten fiber for reinforcement.

View full abstract