Uichi Kubo

Development of a coating technique for inertial confinement fusion plastic targets

Deuterated polystyrene as a target material offers several advantages over other polymers because of the following: (1) it is chemically and physically stable at ordinary conditions, (2) it can be easily formed into spherical shells, and (3) it has a very high fraction of D2/H2 (above ∼99%). As in our previous studies, the fabrication method was basically a utilization of the emulsion technique. This method is well suited to mass‐producing the polymer targets without microprocessing techniques. We have developed a fabrication method for single shell targets and an extension of this technique also enables us to fabricate double shell targets. This new method is faster and less labor intensive than previous techniques. The development of ICF experiments requires multilayer structure targets; we have developed, moreover, a new fabrication technique called the multicoating method. The polymer coating can be fabricated by the application of an emulsion technique. On the other hand, with metal coating, a nonelectroplating method was used, and nickel was employed as the coating metal. The thickness of the polymer coating layer can be controlled with the rotational speed of a stirrer in the emulsion. In the case of nickel coating, it is achieved by controlling the plating bath temperature and immersion time during the plating process. The experiment resulted in the development of a new technique for the fabrication of multilayer targets and low density, thick polymer‐layer‐coated targets.

Electrical breakdown in cryogenic liquids

Abstract Both the statistical time lag T s and the formative time lag T f of the breakdown in cryogenic liquids (Liq.Ar, N 2 and He) are evaluated from the Laue plots of the breakdown time lag induced by a voltage pulse having a 100-ns pulse width. In the case of Liq.Ar, both T s and T f become shorter with increasing applied voltage, and T f increases with increasing electrode distance under the constant electric field. Therefore, these experimental results are interpreted in terms of a single avalanche mechanism. On the other hand, in the case of Liq.N 2 , T s decreases with increasing electric field, but T f does not depend strongly on the electric field. In Liq.He at both 4.2 K and 2.1 K, T s and T f show a similar tendency as with Liq.Ar. In Li He, the threshold breakdown field decreases with increasing electrode distance and voltage pulse width. The carrier mobility, estimated from T f by assuming a single avalanche breakdown, is nearly the same as that obtained by the time-of-flight method in Liq.Ar. In Liq.He, however, the former is larger than the latter obtained at low fields. Under the non-uniform electric field (plane-needle electrode configuration), the breakdown strength at negative needle configuration is much higher than that at positive needle in Liq.Ar. On the contrary, in Liq.He the former is much lower than the latter. These experimental results can be interpreted by taking into consideration the different mobilities of negative and positive carriers in these liquids.

Raman Scattering in Nematic and Smectic Liquid Crystals

Raman spectra and their temperature dependence were studied in several nematic and smectic liquid crystals. The characteristic low frequency modes were observed in azoxy bonded liquid crystals such as PAA, AAB, but not in anile bonded liquid crystals such as MBPA, EBHA, ABHA. However in OHMBPA (OH substituted MBPA) such a mode was also observed. These low frequency modes were interpreted in terms of the collective low frequency modes due to the strong intermolecular interaction such as a dipole-dipole interaction or a hydrogen bond. Raman intensity of EMBAC sandwiched between two rubbed glass plates changed quite smoothly at the smectric-nematic transition, which is interpreted in terms of a second order phase transition.

Optical Beam Guides For Medical CO 2 And Excimer Lasers

The metal and polymer compound hollow tube is effective guide for cw CO2laser beam transmission. We have tride to high peak pulse CO2laser beam delivery with the hollow tube guide. Using the CO2 pulse laser have high peak (46MW max. ,short pulse width(80ns) and repeat pulses(under lOpps). In this experiments, the laser beam transmittance was obtained ca.90%/m. So the hollow tube are confirmed as useful beam guide technique for also pulse CO2 laser. We are having also investigates of UV laser beam transmission with the hollow tube as CO2 laser beam. We have used KrF excimer laser(248nm wavelength). We found that the random polarized beam transmittance was ca.26%/m, if polarized beam was ca.37%/m, delivery average power and energy were ca.1 watt(220kW peak power) and 5m.J. per pulse respectively. On the other hand, we have been developing UV optical fiber for Kr F laser, Results so far were obtained above 80%/m transmittance by OH ion added quartz glass fiber.

Development of polyvinyl alcohol shells overcoated with polystyrene layer for inertial confinement fusion experiments

In inertial fusion experiments, the use of polymer shells provides more efficient ablative implosion and significantly reduced radiation preheat compared with the glass shells currently used. We have developed a method of fabricating polyvinyl alcohol (PVA) shells overcoated with a polystyrene (PS) layer. The method utilizes the emulsion technique previously developed by us, and employs three different liquid phases. A 5 wt. % aqueous PVA solution is mixed with a 7 wt. % PS solution in dichloromethane while stirring. The mixture is then poured into a 1 wt. % PS solution in cidhloromethane while stirring. The mixture is then poured into a 1 wt. % aqueous gelatin solution. The resulting emulsion is heated to evaporate the dichloromethane, resulting in solid PS shells encapsulating the PVA solution. The PS shells are subsequently washed and dried in vacuum to drive off the remaining water. As a result, a PVA shell is formed inside an overcoating PS shell which exhibits a good surface quality in the outer dia...

Fabrication of large‐sized polystyrene shells

A simple method to fabricate a large‐sized polystyrene shell has been developed for use in future inertial confinement fusion experiments. The fabrication technique is based on the emulsion method. Important improvements to the previous technique are that the water phase of the emulsion is gelled by cooling and an oil phase is not stirred in a formation of a water/oil emulsion. In addition, the densities of water and oil phases are adjusted to remove the effect of gravity. The fabricated shells had diameters up to 6.2 mm.

Fabrication of cross-linked polymer shells for inertial confinement fusion experiments

For inertial confinement fusion experiments, a copolymer of acrylonitrile and styrene (AS) shell overcoated with a cross-linked polyvinyl alcohol (PVA) has been fabricated in order to obtain good gas-barrier properties and resistance to beta decay of tritium. The fabrication method is based on the emulsion method using the interfacial poly-condensation reaction between water and oil phases. Cross-linked PVA with a thickness of 5 μm has been successfully overcoated on an AS shell. The surface roughness has been estimated using an atomic force microscope to be 0.5 nm (root mean square).

Carrier mobility in vinylidenefluoride-trifluoroethylene copolymer

The carrier mobility of a ferroelectric Vinylidenefluoride-Trifluoroethylene copolymer (VDF: 54 mol%) was measured by the time-of-flight method after irradiation by a KrF excimer laser. The hole and electron mobilities were estimated to be 3×10-6 cm2/Vs and 7×10-6 cm2/Vs, respectively.

Effect of Microwave Polarization on Absorption by Cylindrical Plasma

The effects of microwave polarization were found in a certain condition of plasma during measurements of transmitted-wave attenuation and phase shift through the cylindrical plasma using a square microwave horn. (R.E.U.)

Excimer laser beam delivery systems for medical applications

We have been doing the basic experiments of UV laser beams and biotissue interaction with both KrF and XeCl lasers. However, the conventional optical fiber can not be available for power UV beams. So we have been investigating about UV power beam delivery systems. These experiments carry on with the same elements doped quartz fibers and the hollow tube. The doped elements are OH ion, chlorine and fluorine. In our latest work, we have tried ArF excimer laser and biotissue interactions, and the beam delivery experiments. From our experimental results, we found that the ArF laser beam has high incision ability for hard biotissue. For example, in the case of the cows bone incision, the incision depth by ArF laser was ca.15 times of KrF laser. Therefore, ArF laser would be expected to harden biotissue therapy as non-thermal method. However, its beam delivery is difficult to work in this time. We will develop ArF laser beam delivery systems.