Hisamitsu Mitera

Formation of Drawing- or Radiation-Induced Defects in Germanium-Doped Silica Core Optical Fiber

The influence of the drawing process in optical fibers on the radiation resistance property was investigated. The ESR spectra for the optical fibers drawn under various conditions were measured at room temperature (R.T.) or 77 K. The fibers were drawn at three different temperatures (high, medium and low) and the drawing velocity was kept constant. The drawing defects were abundantly detected at R.T. in the sample drawn at high temperature. Many non-bridging oxygen hole centers (NBOHC) induced during the drawing process were observed at 77 K. The formation of NBOHC was also discussed.

Evaluation of Microwave Conductivity in Superconductor YBa2Cu3O7-x Using a Cavity Perturbation Technique

The microwave properties of a YBa2Cu3O7-x bulk sample are investigated using a cavity perturbation technique. The sample is placed in the field of a microwave TM011 mode cylindrical cavity operated at about 2.86 GHz, and the unloaded quality factor QU is measured in the temperature range above 80 K. It is found that a sharp reduction of the Joule loss in the sample begins at an onset temperature of about 90 K. The formula for the microwave conductivity is also derived theoretically and the conductivity of the sample is evaluated from the results of QU measurements of the cavity with and without the sample.

Improved Microwave Cavity Measurements for the Density and Collision Frequency in Decaying Plasmas

Well known microwave cavity measurements for determining the plasma density n and the collision frequency v of electrons was improved to be applicable in a simple way to decaying plasmas. Previously, two different microwave frequencies have been required to determine both of the plasma prameters. In the present study we analyzed the general properties of a cavity, and propose an improved method to measure, simultaneously, n and v in a decaying plasma by using only one frequency. The principle is that both parameters are determined by detecting the phase in addition to the absolute value of the transmission coefficient through the cavity. Moreover, we derive various formulas that are useful for measuring both parameters under various assumptions. Various experimental demonstrations for our methods are carried out.

New Method of Decreasing the Oil Surface Potential in a Tank with an Electrostatic Screener

The discharging effectiveness of 100 and 200 mesh stainless screens fixed on top of a diffuser at the oil inlet to a 40 and 500 liter test tank is evaluated. To study the discharging mechanism in detail, the potential distribution along the axis of the test tanks, the ground current at each section of the oil - flow system, and the potential on the oil surface of the test tanks were measured. It was found that the peek potential along the axis of the tanks and the surface potential of the oil in the tanks was considerably reduced when either the 100 or 200 mesh screens were fitted. The screens were found to have some discharging effectiveness and lowered the potential not only on the surface but in the oil by reducing the oil velocity and changing the distribution of the charge density.