Tohru Tamagawa

Post Arc Current in Vacuum Interrupters

Detailed measurements of post arc current in a vacuum were made and the results were compared with theory. This comparative study was particularly characterized by conducting post arc current measurements following high arc current (36 kA rms maximum). Three kinds of electrode materials and two types of electrodes were used to elucidate effects of the electrode materials and the types on post arc current. Shield current was also measured to clarify the characteristics of the ion current. The characteristics of post arc current are explained by referring to those results.

Development of Vacuum Interrupters with High Interrupting Capacity

Vacuum interrupters, in which axial magnetic field type electrodes and CuCr contact materials are ccnbined, show excellent performance from all points of view. By this combination of electrode and contact material, the arcing phenomenon is scmewhat different from that of existing combinations. We have investigated the arcing and dielectric phenanena in detail and have found the optimum conditions. As a result, the new vacuum interrupters were developed in which interrupting capabilities have been improved. The application range is fran 12 to 84 kV in rated voltage and up to 5OkA in interrupting current. This type of vacuum interrupter was utilized widely in general field applications.

The Applications of Axial Magnetic Field Electrodes to Vacuum Circuit Breakers

A special electrode structure for a vacuum interrupter in which an axial magnetic field, generated by the electrodes, stabilizes the arc and consequently increases the interrupting ability, has been invented.

Post-Arc Current After High-Current Interruption in Vacuum

Detailed measurements of post-arc current in a vacuum were made. This investigation was particularly characterized by conducting post-arc current measurements following high arc currents (36 kA rms maximum). Postarc current increases with main arc current, and shows a sharp increase when the main arc current reaches certain value. The magnitude of post-arc current for each contact material differed; the descending order is Cu-Bi > Cu > Cu-W > Ag-W. Shield current was also measured to clarify the characteristics of the ion current. Cu-Bi > Cu > Cu-W > Ag-W was the descending order of measured shield current. The characteristics of post-arc current are explained by referring to those results.

Effect of Axial Magnetic Fields on Electrical Characteristics of Low-Pressure Wire Discharge.

In order to reveal the potential of wire discharge as a high-density-plasma source, electrical characteristics of a wire discharge plasma were investigated, in particular, taking note of the effect of axial magnetic fields. The dc breakdown voltage and the delay time of a pulse discharge were measured in the presence of an axial magnetic field. When a single-wire anode is adopted, the effect of the magnetic field is very small. On the contrary, in the case of adopting two parallel anode wires, the axial magnetic field affects the discharge properties considerably.

3 kHz XeCl Excimer Laser Using New Type of Electrode

A new type of electrode for XeCl excimer lasers has been developed. In order to produce a stable discharge at a high repetition rate, we calculated the electric field strength distribution of the discharge area, using the finite-element method. On the basis of the calculation results, we fabricated a new type of electrode, applied it to an XeCl excimer laser, and operated the laser at a repetition rate of 3 kHz. The laser power during 3 kHz operation was 18.9 W with the Ernst-type electrode and 24.4 W with the new-type electrode. The space distribution of density variance due to gas expansion in the discharge area could be checked by the laser schlieren method. With the Ernst-type electrode, the energy is concentrated in the center of the discharge area. With the new-type electrode, in contrast, the energy concentration is reduced, making the discharge stable.

Uniform Field Electrodes for High-Power and High-Repetition TEA-CO2 Lasers

A new electrode system has been specially developed for high-power and high-repetition transversely excited atmospheric (TEA)-CO2 lasers. The new system produces a uniform glow discharge compared that in a conventional Chang electrode system. In this new system, the laser beam energy profile shows a nearly flat top configuration and the repetitive rate of maximum output power has been increased from 175 Hz to 350 Hz. The discharge energy density profile is calculated to estimate the influence of gas density fluctuation. The numerical result shows that the maximum fluctuation of gas density is 10% less in this electrode system.

Long-pulse high-repetition-rate transversely excited CO2 laser for material processing

Using a TE-CO2 laser, we could obtain a long-pulsed laser beam of low initial spike by controlling the discharge current by a pulse forming network and optimizing the gas composition, discharge length to resonator length ratio, and output mirror reflectivity. The maximum laser output was 1.1 J; the initial spike energy, 100 kW; the tail output, 56 kW; and the 16 (mu) sec (FWHM). The maximum repetition rate was 500 Hz. A new type of circuit with small pre-ionization current made it possible to operate the laser at a high repetition rate so as to prolong the laser life. When a 5-inch lens was used, the laser power density at the focal point was 1*108 W/cm2, making it possible to use the laser with an unusually high energy density without causing the breakdown of air insulation. In fact, we succeeded in fine- cutting a 0.5 mm thick alumina ceramic with the laser. It was found that unlike other working methods, the newly developed laser does not cause cracks in ceramic work pieces.

Electrical characteristics of a low pressure wire discharge and an application to high current density electron gun

Abstract The electrical characteristics of a wire discharge plasma were investigated, in particular, taking notice of the effect of electron trapping by axial magnetic fields. It was found that the plasma property changed remarkably, when the magnetic fields were applied. This property may be used to control the wire discharge plasma. The wire discharge plasma plays an important part as an ion source of an ion-induced secondary emission electron gun. This type of electron gun was demonstrated. The maximum electron beam current obtained was 90mA/cm 2 at beam energy of 100keV. In our calculation model, the secondary emission coefficient γ is 12.0 for 100keV helium ion and the electron beam extraction efficiency β obtained is 0.35.

Discharge-pumped excimer laser with high-speed and low-temperature gas flow

A high-speed wind tunnel, made by using a Ludwieg tube, has been successfully developed for a highly repetitive discharge-pumped excimer laser. This apparatus allows the gas flow of velocity approximately 204 m/s, pressure approximately 293 kPa, temperature approximately 254 K, and duration time approximately 48 ms. The rate constant for the recombination process of Xe+ + Cl- + Ne yields XeClX + Ne is found to increase to a maximum of 4.2 X 10-6 cm3/s at 180 K in a gas pressure of 294.2 kPa. The kinetic simulation of XeCl excimer laser using such a rate constant indicates the enhancement of the laser output in the lower gas temperatures.