Etsuo Noda

Radon concentration dependence of alpha radioactivity measurement using ionized air transportation

We are developing an alpha radioactivity measurement apparatus for uranium contaminated waste with large and complex surfaces (alpha-clearance monitor). This monitor uses the alpha radioactivity measurement method using ionized air transportation. Our goal of the monitor is to measure 4 Bq of alpha radioactivity for a 10 minutes measurement (5.7 Bq at present). A problem in achieving the goal is fluctuation in the background (BG) ion current. This fluctuation is predicted to be mainly due to radon inside the monitor. Therefore we developed a method to measure the radon concentration inside the monitor without an additional radon detector which disturbs airflow. And as a preliminary study, we determined the radon contribution to the BG current using this method. In addition, ion mobility and ion recombination coefficient, which are the other factors influencing the detection limit, were measured and evaluated under various environmental conditions (temperature, humidity and aerosol density).

Development of a 10-kW solid state pulse power supply for copper vapor lasers

We have developed a magnetic-pulse-compression-type 10-kW-class solid state pulse power supply for copper vapor lasers. By triggering the gates of two gate turn-off thyristors (GTOs) connected in parallel, a 5-μs rise time primary pulse was generated. A three-stage magnetic pulse compression circuit compressed the primary pulse to 0.13 μs. The 13.7-kW GTO switching energy was achieved with a 4-kHz pulse repetition rate when a dummy load was connected instead of copper vapor laser (CVL). Total energy transfer efficiency of the power supply was 60%. This pulse power supply has been applied to a CVL with a plasma tube of 70-mm inner diameter and 1.5-m discharge length, and has operated successfully.

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.

Development of solid state pulse power supply for copper vapor laser

The authors have developed a magnetic-pulse-compression type solid-state pulse power supply. The lifetime of a solid-state device is expected to be much longer than that of a thyratron. Two parallel connected gate-turn-off thyristors generated a long pulse, which was compressed to 0.27 microsecond(s) ec by a three-stage magnetic pulse compression circuit. The average power of 8.2 kW was able to be obtained when a dummy load was connected instead of copper vapor laser (CVL). This pulse power supply has been applied to a CVL with a plasma tube of 70 mm inner diameter and 1.5 m discharge length, and has been successfully operated.

Output characteristics and improvement in beam-profile of large-bore copper vapor lasers

Alumina plates (Gas-cooling plates) were inserted into the plasma tube of copper vapor lasers to cool the buffer gas at the center of the plasma tube. Consequently, the laser intensity increased, especially at the center, and higher output power was obtained. It was revealed by measurement that the gas-cooling plates reduce the buffer gas temperature and the lower laser level density of copper atoms at the center of the plasma tube. Output characteristics were measured by varying the repetition frequency. Plate insertion improved the central intensity at higher frequencies. Output power was most dependent on the frequency with the plate inserted, and increased proportionally as the frequency increased.

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.

The method of ion current measurement on capacitive-coupled plasma

A small device, the conduction current probe, has been developed for the multi-point observation of ion currents. The probes are mounted on an electrode of a capacitive-coupled rf plasma source. The probe obtains the conduction current entering the electrode as a function of time by shielding the rf displacement current. The conduction current consists of the ion current as well as the electron one. The ion current is nearly constant although the electron one synchronizes with the rf electric field and flows in the short time of a rf cycle. Therefore, the ion current is obtained from the constant region of the conduction current. The experiments on a rf magnetron have revealed that the probe is a useful device for studying the parametric properties of the plasma source.

Multiple hollow‐cathode vacuum‐ultraviolet plasma source excited by pulsed glow discharge

A multiple hollow‐cathode vacuum‐ultraviolet source excited by a pulsed glow discharge in a mixture of Xe and He has been developed. A MgF2 window with a diameter of 55 mm was used, and the repetition frequency was varied between 3 and 9 kHz. Stable output was maintained for about 3 h. Measurements of 147 nm radiant illumination were made at various distances from the window at various repetition frequencies. The peak radiant illumination decreased while the average radiant illumination increased with increasing repetition frequency. The output power density near the center of the window could be estimated from the relationship between measured radiant illumination and distance from the window. The peak and average output power densities at 6 kHz were 30 and 1.5 W/m2, respectively.

Output characteristics of a transversely excited copper vapor laser

A maximum output power of 13.2 W was obtained at a high repetition frequency of 5 kHz by a transversely-excited copper vapor laser with an excited volume of 112 cm3. Its specific output power density was 118 mW/cm3. It corresponded to a specific output energy density of 24 (mu) J/cm3. We also examined the dependence of the output power on the buffer gas pressure, the repetition frequency, and the charging voltage.