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IHI developed underwater welding process by using YAG laser and qualified the process to repair a thin wall stainless steel tank in a power plant in Japan. Important features of YAG laser welding are less welding distortion, and a small heat-affected zone (HAZ) due to the smaller heat input and higher cooling rate than with other conventional welding methods. In this study, we have conducted underwater laser welding of Ni-base alloy and stainless clad materials, such as Alloy 600 and E-309L / E-308L clad materials. Alloy 690 was selected as weld filler metal for a corrosion resistant overlay to prevent corrosion attack by the service environment. Welding trials were conducted on the surface of flat plates with simulated surface cracks, and the trial welds were assessed for soundness of welding. The preliminary results of the trial welds by using high power laser diode, and comparison between YAG laser and high power LD are reported.

The experimental setup of the FEL storage ring NIJI-IV was completed in July 1992. This paper will describe the preparation of the electron bunch to 1 or 2 bunch operation at an energy range of 240–300 MeV in order to reach FEL operation at about 600 nm.

The first lasing at around 590 nm of a free-electron laser (FEL) in the storage ring NIJI-IV was achieved on August 18, 1992, though just above threshold. The NIJI-IV is a racetrack-type ring dedicated to FEL, which was completed in December 1990. Though the ring is compact, it has two 7.25-m straight sections. The electron beam was stacked for the first time in February 1991. After a 6.3-m optical klystron was installed in one of the straight sections, FEL related experiments were started at the end of April this year, and oscillation experiments have been carried out since the beginning of August. The electron-beam energy during the lasing was about 240 MeV, and the current was 1.1−0.2 mA/bunch. The laser wavelength ranged from 594.5 to 588.7 nm, and the bandwidth was below 0.4 nm.

We have constructed a racetrack-type compact electron storage ring “NIJI-IV” for UV FEL experiments. The ring has a hexagonal configuration with a circumference 29.6 m. consisting of the two-cell structure of the triple-bend achromat lattice. The length of the straight section is 7.25 m in which a 6.3 m insertion device can be installed. A stored current higher than 200 mA is expected. The first storage of electrons was achieved on February 15, 1991, with an injection energy of 270 MeV. At present, a stored current higher than 70 mA with a lifetime of 20 to 30 min is obtained at full bunch operation (the harmonic number is sixteen).

This paper introduces a new type of cathode-ray tube with a crossed-field electron gun which produces an electron beam in a region where a nonuniform magnetic field and an electric field cross perpendicularly. The new configuration gives increased freedom in the design of crossed-field guns. As a result, a long, directly heated cathode can be readily applied to a gun structure which makes high perveance and instant operation possible with much improved cathode heating efficiency. The new gun provides ion trap action by virtue of a magnetic field which separates ions from electrons due to the difference in their masses. A new type of cathode-ray tube using this gun not only demonstrates these features but also requires relatively low operational voltages for beam acceleration and control electrodes. The paper includes an analysis of electron motion in a crossed field with a nonuniform magnetic field. It also shows practical configuration of electrodes and current characteristics of the gun.

We have constructed cathode-ray tubes utilizing traveling waves, whose deflection sensitivity can be made independent of frequency by equalizing the phase velocity of the wave and the electron velocity. According to the theoretical analysis, the sensitivity of this tube is increased to 10-1mm/v at 30 kMc without any difficulty. The results of the theoretical analysis are proved experimentally by the inversion spectrums. As examples of its application, measurements of amplitude modulation degree and observations of uhf voltage wave form are described in this paper.

This paper introduces a new type of cathode-ray tube with a novel electron gun which produces an electron beam in a region where a nonuniform magnetic field and an electric field cross perpendicularly. The tube has the following features: 1. Increase in the beam current density makes possible a reduction in the accelerating voltage to 6 to 8 kV (that is, 20 to 30% lower than that of ordinary cathode-ray tubes) while maintaining the same screen brightness. 2. By using a directly heated cathode only 0.7 to 1.0 sec is necessary for warm-up, and only about 0.4 watt of heater power is required. 3. By an ion-trap effect, the fluorescent screen is protected from damage caused by negative ion bombardment. Accordingly, the thickness of the metal back layer can be reduced greatly to the limiting value required for good reflectivity. Furthermore, a long life can be expected because of a reduced probability of bombardment of the cathode with positive ions. 4. Cutoff voltage is --20 to -30 volts or about 1/3 to 1/2 that of ordinary tubes. The paper includes an analysis of electron motion in crossed fields with a nonuniform magnetic field. The equilibrium condition required to produce the electron beam in such crossed fields can be derived in terms of the magnetic field distribution function. The paper also shows practical configuration of electrodes and magnet and current characteristics of the gun.