Noriyasu Kobayashi

High-voltage and short-rise-time pulse-transformer with amorphous cores

A short rise time pulsed power transformer using cobalt-based amorphous alloy cores, which operates at high voltage (/spl sim/100 kV) and high repetition rate (/spl sim/4000 pps), has been developed for application as a pulsed power modulator for copper vapor lasers. An output voltage of more than 80 kV, a rise time of 65 ns and a transformation efficiency of 83% were demonstrated for the transformer with a 1.2 step-up ratio. Moreover, using a 1:3 step-up ratio, a maximum output voltage of over 110 kV was achieved. Circuit calculation indicated the impedance matching and coupling coefficient would be improved by the one-turn primary coil and short magnetic path length from primary to secondary coil. This paper describes the design procedure and the experimental and analytical results respecting the transformer characteristics.

Compact soft X-ray source for biological applications

A compact soft X-ray source with carbon nanotubes (CNTs) based field emission electron source is being developed for applications to biological, medical and material technology fields. In the tests using a diode-type source, the maximum current of 13 mA (density of over 50 mA/cm/sup 2/) was extracted from the CNTs emitters (0.26cm/sup 2/) at electric field of about 6 V//spl mu/m and 2.5 /spl times/ 10/sup -5/ Pa pressure. In addition, a triode-type source was designed to obtain a pencil-like soft X-ray beam. Geometrical parameters in the source were optimized using calculation codes for electric fields and electron beam orbits. The X-ray source was stably operated, and the electron beam current of 0.24 mA was obtained at the applied anode voltage of 35 kV. Based on the numerical estimations, it is expected that the focal size is about 0.5 mm, and the X-ray beam density is 1.5/spl times/ 10/sup 7/ photons/s with the divergence angle of 30 mrad.

Basic Characteristics of Eddy Current Testing Using Resonant Coupling

It has been demonstrated that magnetic resonant coupling is effective for improving the characteristics of ECT sensor, especially the lift-off-dependent reduced sensitivity and noise. The lift-off-dependent reduced sensitivity and noise are caused by the decrease of voltage gain from the exciter coil to detector coil. Magnetic resonant coupling is generally usable to increase the voltage gain from the transmitter coil to the receiver coil. Magnetic resonant coupling was applied to ECT in these experiments to investigate the phenomena of magnetic resonant coupling in the ECT. In the ECT setup, the voltage gain G increased more than 6 times by magnetic resonant coupling at a frequency of 105 kHz. The voltage gain ratio (GR/GNR) was rising 1.12 times when the lift-off length increased from 1mm to 2 mm. This result verified that magnetic resonant coupling has the potential for improving the characteristics of ECT. The EDM slit signal and the lift-off noise were calculated from the experimental results, respectively. Using magnetic resonant coupling, the EDM slit signal increased 1.5 times and the lift-off noise was reduced by 34 % at a lift-off length of 2mm. these results confirmed that magnetic resonant coupling is effective for improving the characteristics of ECT. Additional experiments were performed in order to verify the effect of magnetic resonant coupling for the wobbling (lift-off) noise in the tube inspection. In the vibration test of the ECT sensor inside the tube, the lift-off noise decreased by 28 % on average by magnetic resonant coupling. In the scanning test of the ECT sensor inside the tube, the wobbling and other noises were obviously reduced by magnetic resonance coupling.Copyright

Remote Field Eddy Current Testing for SG Inspection of Fast Reactor

We confirmed defect detection performance of a remote field eddy current testing (RFECT) in order to inspect a helical-coil-type double wall tube steam generator (DWTSG) with a wire mesh layer for the new-type small fast reactor 4S (Supersafe, Small and Simple). As high sensitivity techniques, to increase an indirect magnetic field intensity, we focused attention on increasing a direct magnetic field intensity in the vicinity of an exciter coil by the use of an exciter coil with a magnetic material (flux guide). We adopted horizontal type multiple detector coils with flux guides arrayed circumferentially to enhance sensitivity of radial direction. According to the experimental results, the indirect magnetic field intensity (the voltage of detector coil in the region of indirect magnetic field) increased more than 100 times by the application of the exciter and detector coils with flux guides. Finally, we detected the pinhole defect of 1 mm in diameter and 20% of outer tube thickness in depth over the wire mesh layer by the adoption of the flux guides and horizontal type multiple detector coils. And we confirmed that the RFECT probe is also useful to detect the thinning defects.© 2010 ASME

Development of high-power copper vapor laser system

A high power copper vapor laser (CVL) system in master oscillator power amplifier configuration has been developed for laser isotope separation program in Japan. Maximum output power of 650 W has been successfully achieved with 9- cm diameter and 350 cm discharge length amplifier. Also MOPA output power of 2.4 kW has been demonstrated in small master oscillator with 4 cm bore and 4 stage power amplifier with 9 cm bore configuration. The authors developed a thermal calculation code to maintain an optimum copper vapor density throughout a large volume and a new thermal insulation structure design method has been proposed to combine two different heat insulators to make longitudinal temperature distribution of the laser tube as flat as possible. A CVL discharge circuit has been improved by applying an excellent magnetic switch which prove a approximately 90 kV-4000 A pulse to a CVL at 4.4 kHz repetition rate. This paper reports such CVL design methods together with the performance of the designed high power CVL system.