Masanori Akazaki

Bio: Masanori Akazaki is an academic researcher from Kyushu University. The author has contributed to research in topics: Laser & Impulse (physics). The author has an hindex of 17, co-authored 145 publications receiving 1055 citations. Previous affiliations of Masanori Akazaki include Kumamoto University.

Influence of Wind and Conductor Potential on Distributions of Electric Field and Ion Current Density at Ground Level in DC High Voltage Line to Plane Geometry

Abstract: Lateral profiles of electric field and ion current density at ground level were measured precisely in a unipolar/bipolar line to plane geometry under different wind conditions and different dc voltages. Furthermore, the relationship between the field and current density is discussed. In the case of unipolar line in still air, the normalized profiles are approximately independent of the magnitude of the applied voltage and the linear dimensions of the gap, but they are strongly influenced in the bipolar case. The wind effect on the current profile is greatest at voltages close to corona onset for each experimental arrangemeht. The experimental results suggest that the usual wind extends the region of the ionic current flowing . e. the right-of- ay required for HVDC transmis-sion lines) by a factor of two or more as compared with that with no wind.

Applications of the Fraunhofer-diffraction method for plasma-wave measurements

Abstract: The improved theoretical analysis of Fraunhofer-diffraction method as a new means to measure the frequency, wavenumber, intensity and even spatial position and propagating direction of plasma waves is presented. It is further, experimentally verified and the measuring accuracies are ascertained by measurements in a microwave region, of ion-acoustic waves in a DC discharge. Successes of introducing the practically important conditions into theoretical analysis have made it possible to establish this method as a standard and powerful diagnostic technique for measurements of plasma waves and turbulences in various plasmas such as in Tokamaks.

Effects of Mechanicl Stresses on the Dielectric Breakdown Strengths of PET and FRP

Abstract: Organic materials to be used for the electrical insulation of superconducting magnet coilsin large fusion reactors must withstand electrical stresses under high mechanical loads, extreme temperatures, and intense nuclear radiation. In this paper, measurements at room temperature are reported on the effects of mechanical compressive and tensile stresses on the dielectric strengths of bi-stretched polyethylene terephthalate (PET) and epoxy glass cloth (FRP, G-10) which are widely used for the insulation of superconducting magnet coils. For PET, the breakdown strength increases with increase of compressive stress in the region of elastic deformation but decreases in the region of inelastic deformation. The value of compressive stress showing maximum dielectric strength is independent of film thickness and is approximately 100 MPa, smaller than the stress appearing in large fusion reactors. In the case of FRP, the behavior of breakdown characteristics under compressive stress is nearly the same as that of PET but the relationship between characteristics of electrical breakdown strength and mechanical properties of FRP isnotclear because it is a composite of two materials: epoxy resin and glass filler. The effect of tensile stress on the dielectric strength is small for PET, but significant for FRP.

Energy Dependence of Angular Distributions of Sputtered Particles by Ion-Beam Bombardment at Normal Incidence

Abstract: The angular distributions of sputtered Fe-atoms were measured using the laser fluorescence technique during Ar-ion bombardment for energies of 0.6, 1, 2 and 3 keV at normal incidence. The measured cosine distribution at 0.6 keV progressively deviated to an over-cosine distribution at higher energies, and at 3 keV the angular distribution was an over-cosine distribution of about 20%. The experimental results agree qualitatively with calculations by a recent computer simulation code, ACAT. The results are explained by the competition between surface scattering and the effects of primary knock-on atoms, which tend to make the angular distributions over-cosine and under-cosine, respectively.

Field reversed configurations

Abstract: The review is devoted to field reversed configurations and to the related field reversed mirrors; both are compact toroids with little or no toroidal magnetic field. Experimental and theoretical results on the formation, equilibrium, stability and confinement properties of these plasmas are presented. Although they have been known for about three decades, field reversed configurations have been studied intensively only in recent years. This renewed interest is due to the unusual fusion reactor potential of these high beta plasmas and also to their surprising macroscopic stability. At the present time, field reversed configurations appear to be completely free of gross instabilities and show relatively good confinement. The primary research goal for the near future is to retain these favourable properties in a less kinetic regime. Other important issues include the development of techniques for slow formation and stability, and a clearer assessment of the confinement scaling laws.

Laser Techniques for the Quantitative Detection of Reactive Intermediates

Abstract: An overview is given of recent developments in laser diagnostic methods for the quantitative measurement of trace species concentrations and, in conjunction, of temperature in combustion systems. After a short introduction illustrating some experiments from the pre-laser era, the article presents typical applications and discusses advantages and limitations of laser techniques including laser absorption, linear, saturated, predissociative and multi-photon-excited laser-induced fluorescence (LIF), resonance-enhanced multiphoton ionization (REMPI), electronically resonant coherent anti-Stokes Raman scattering (resonance CARS), degenerate four-wave mixing (DFWM) and amplified spontaneous emission (ASE). Recent trends including two-dimensional imaging, multi-species detection and high-pressure applications will also be discussed. Throughout the article, an attempt is made to present typical results from a large portion of the relevant technical literature. A concluding section gives a short summary of the current status and comments on the perspectives for further research.

Effects of focusing on third-order nonlinear processes in isotropic media. [laser beam interactions

Abstract: A theoretical analysis of third-order nonlinear interactions of focused laser beams is performed for the processes \omega_{1} + \omega_{2} + \omega_{3} \rightarrow \omega_{4}, \omega_{1} + \omega_{2} - \omega_{3} \rightarrow \omega_{4} , and \omega_{1} - \omega_{2} - \omega_{3} \rightarrow \omega_{4} . The total power and far-field beam profile of the generated radiation is related to the total powers of the fundamental beams, to the tightness and location of the focus, and to the value of the difference between the wave vectors of the generated radiation and driving polarization. The optimum degree of wave-vector mismatch as a function of tightness and location of focus is determined for each of the three processes. The process \omega_{1} + \omega_{2} - \omega_{3} \rightarrow \omega_{4} is found to be unique in that it is always optimized by focusing as tightly as possible. Experimental results, which verify the theory for the processes \omega_{1} + \omega_{2} + \omega_{3} \rightarrow \omega_{4} and \omega_{1} + \omega_{2} - \omega_{3} \rightarrow \omega_{4} , are presented.

A review of the charge simulation method and its applications

Abstract: The author provides a comprehensive review of the basic charge simulation method and its various modified versions reported in the literature. Applications of the charge simulation method, alone as well as in combination with other methods, are considered. Different aspects of this method are critically examined and its potentials and limitations are identified. Possible areas of future research are outlined in order to improve the overall effectiveness of computer-aided analysis and design of high-voltage insulation devices by using the charge simulation method. >