Osami Morimiya

Theoretical and experimental study of a high‐current vacuum arc in a uniform axial magnetic field

Measurements of the electron temperature, floating potential, plasma density, and average plasma pressure in a magnetically confined high‐current vacuum arc are described. A 40‐mm‐diam, 30‐mm‐long arc was initiated between OFCu copper electrodes in a uniform axial magnetic field by triggering the gap. The crest values of the arc current ranged from 3 to 20 kA. The electron temperature by Langmuir probe measurement was Te= 2.5–3.0 eV with a uniform space distribution and was independent of the arc current. The space distribution of the ion density was parabolic in the radial direction and with a zero derivative in the axial direction. The average plasma pressure by paramagnetic measurement increased with the square of the arc current. The experiment showed that the arc column could be considered as an infinitely long column in which the plasma parameters have zero axial derivatives. Theoretical analysis has been carried out under the following assumptions. An infinitely long cylindrical and fully ionized s...

Improvement in the Output Characteristics of a Large-Bore Copper Vapor Laser by Hydrogen

It has been experimentally confirmed that addition of about 1% hydrogen gas to the copper vapor laser (CVL) discharge improves the output characteristics of a large-bore CVL with 80 mm beam diameter and 1500 mm discharge length. The annular distribution of the beam intensity became uniform and the output power increased. The increase in the green laser power was larger than that in the yellow one. The hydrogen gas addition was effectual when the input power to the discharge was large and the copper temperature was high. A 120 W output power was obtained continuously for 26 hours.

Measurement of Instability Initiation Current in Vacuum Arc

The arc current for initiating the appearance of noise on a current trace, the instability initiation current I0, and the arc voltage V0 corresponding to I0, have been measured using Cu-Ni alloy and Ag-Pd alloy electrode metals. The average values of I0 and V0 were plotted as a function of the thermal conductivity λ, showing a decrease with decreasing λ under a constant vapor pressure Ph.

Copper density measurement of a large-bore CVL

The ground state and the lower laser level copper densities were measured in a large-bore copper vapor laser (CVL). The beam diameter was 80 mm, the discharge length 1500 mm, and the output power about 100 W at an operation of a repetition frequency 5 kHz. A new laser-absorption method has been developed to measure the copper ground state density. The measured copper density of the ground state was 1 to approximately 5 X 1021 m-3 and the radial profile was hollow. The profile can be explained from the radial gas temperature profile. The lower laser level (metastable state) densities were measured by the ordinary laser-absorption method. The density of the lower laser level for green emission was about 1 X 1018 m-3 and that for yellow emission was about 3 X 1017 m-3 at the center. The lower laser level densities were higher at the center than near the wall in contrast with the ground state density.

Glow Auxiliary Electrical Discharge for CW High-Power CO2 Lasers

A new discharge technique for DC glow auxiliary electrical discharge (GAED) lasers has been developed in order to realize efficient, stable and compact CW transverse-flow high-power CO2 lasers. The auxiliary discharge power source for GAED is common to that of the main discharge. This paper describes the discharge technique and characteristics of GAED. The luminous region of the positive column with auxiliary discharge became wider and more uniform than that without auxiliary discharge. The limited glow discharge power Wg* (the discharge power for initiating unstable glow discharge) with auxiliary discharge was about 2.2 times that without auxiliary discharge. It was also found that the maximum value of Wg* was obtained when the CO2 gas mixture ratio was 2-4%.

Discharge And Output Characteristics Of CW-CO 2 Laser With Auxiliary Glow-DC-Discharge

A transverse-flow, cross-discharge cw-C02 laser with an auxiliary glow-DC-discharge was developed. The maximum input power increased twice to four times as large as that without the auxiliary discharge. A single-path resonator with 65 mm-aperture and a Z-path resonator with 45 mm-aperture were set up. The output power exceeding 3 kW was obtained for both type resonators with 40 cm-long-discharge area. We deduced an equation which gave the output power for the Z-path resonator. The calculated results agreed with the measured output power.

Effect of electrical conductivity anisotropy on the properties of a high-current vacuum arc

The steady state characteristics of a magnetically stabilized high current vacuum arc were analyzed, taking into account the electron density dependent electrical conductivity anisotropy due to a magnetic field. A marked difference in plasma characteristics between the case of isotropic conductivity and the case of anisotropy conductivity arises in the pressure balance of the arc column and in the axial current distribution. The electron density dependent anisotropy factor of Braginskii¿s theoretical formula and tentative mathematical formulas are discussed. The measured are pressure agreed well with the analytical value obtained from the tentative mathematical formula. A more critical analysis should be applied to the validity of Braginskii¿s formula.

Radial Profiles of Electron Density and Current Components at Cathode Surface in LaB6 Hollow Cathode Arc

Experimental studies on a hydrogen-fed LaB6 hollow cathode arc have been pursued. The plasma parameter in the cathode has been measured by a Langmuir probe. The radial variation in the electron density inside the cathode was calculated using the continuity and momentum equations, showing good agreement with the experimental results. The electron density at the cathode surface was estimated to be 15%–20% of that at the cathode axis. It was also found from the current balance that the arc current components at the cathode surface consist of a thermionic current which takes into account the Schottky effect, the ion current and the secondary electron current induced by ion bombardment. The ion current and the cathode surface is larger than the electron current emitted from the cathode.