Yasutomo Ozawa

A New Numerical Method for Asymmetrical Abel Inversion

A new asymmetrical Abel inversion is presented for application in asymmetrical data which is obtained from plasma diagnostics (for instance, interferometry or spectroscopy) on the toroidal plasma system, and in which asymmetry exists normal to the direction of observation. In this new numerical method a weight function, which was obtained by separating the integrated quantity into odd and even parts, was used for determination of the asymmetrical local value. To demonstrate the usefulness of this new method, we set up a hypothetical data set, which resulted in a valid local value.

Application of light polarization technique to the generalized line‐reversal method for gaseous temperature measurements

The light polarization technique was applied to the generalized line‐reversal method in order to improve the inherently restricted resolution characteristics found in the conventional method using a chopper or a knife wedge, which discriminate the reference lamp light from the gaseous emission either temporally or spatially, respectively. In the proposed method, each of the lights was linearly and perpendicularly polarized and was detected through the same spatiotemporal optical path. The applicability of this method to measure the hot gaseous temperature was confirmed experimentally in a shock tube MHD power generation system.

Solution of Neutron Transport Equation by Superposition of Beams

The analytical solution of the isotropic, one-dimensional and time-dependent transport equation is expressed by the superposition of a newly defined Green function of the virgin neutron flow. As a result, the solution of the neutron transport equation is given by the superposition of beams possessing wave fronts. The present study has introduced the possibility of clearly explaining neutron transport behavior by beam processes, thus providing a further insight into the interpretation of the transport equation. This method should prove useful when the continuous mode is superior to discrete modes. The solution for the stationary case is also derived.

Suppression and utilization of spurious pulse occurrence in organic GM-counters

The authors have made a study of suppression and utilization of spurious pulse occurrence in organic GM-counters. Almost all spurious pulses in the organic GM-counter are the delayed pulses which occur being dependent upon the radiation intensity. The occurrence rate of the delayed pulses against the radiation intensity is affected by the intensity of the electric field in the vicinity of the cathode of the GM-counter. The occurrence of the delayed pulses can be suppressed when the electric field in the vicinity of the cathode is kept at high value. On the contrary, the occurrence of the delayed pulses can be utilized for the dosimetry of the pulsed radiation by means of increasing the space of the weak electric field in the GM-counter.

An Application of Information Theory to Pulsed Nuclear Radiation Measurement

A new method for pulsed radiation measurements is studied by an application of the information theory of discrete systems. It is derived from entropy concept that in order to measure the photon density with the maximum conversion rate of a counter subjected to pulsed photon beams, the density λ of a Poisson source must satisfy the relation of λb=ln 2 when the resolving time τ of the counter lies between the pulse width b and the period (1/f). Actual devices using feedback circuits for satisfying the above condition are proposed.

Simplified theory of nonuniform electrical conduction for an open cycle MHD generator with shaped magnetic induction

Abstract Simplified formulae were derived for the approximate evaluation of electrical performances of an MHD generator with nonuniform equilibrium plasma. In order to clarify the effectiveness of the propperly shaped nonuniform magnetic induction of type B ∞ n e , the transverse component B y was included in the formulation of the theory. It was shown that the terminal characteristics of the generator, such as the internal resistance, the motional emf, the current and the output power could be improved significantly under the shaped B z ∞ n e type of applied magnetic induction for wide ranges of electrodeand insulator wall temperatures, channel sizes and averaged intensities of the magnetic induction.

Analysis of Fast Neutron Pulse by Superposition of Wave Modes

Phenomena engendered by the fast neutron pulse are analyzed by Neumann series solution of the reduced three-dimensional neutron transport equation. The spectral functions of collision neutron fluxes are derived by Fourier-Laplace transform, and the time-, space-, energy-dependent collision neutron fluxes possessing definite wave fronts are obtained with use made of convolution theorems in Fourier-Laplace analysis. Thus, the behavior of fast neutron pulses is described in terms of a superposition solely of wave modes. The present study has deepened our understanding of the detailed physical process of fast neutron pulses, and the process of their formation on the asymptotic mode is clearly explained by wave processes. This treatment has provided a clear explanation of the short time phenomena shown by pulsed neutrons, and should prove useful for analyzing situations where the continuous mode prevails over the asymptotic mode. The experiment of the nano-second order fast-neutron pulse is also analyzed.

ELIMINATION OF BEAM-DEFOCUSING EFFECTS DUE TO FILAMENT MAGNETIC FIELDS IN THE ELECTRON GUN OF A LINAC.

Abstract Beam-defocusing effects of magnetic fields due to the filament current of the electron gun in an electron linear accelerator was eliminated by switch-off of the filament current at the instant of pulsed acceleration. An increase of 30% in beam current density was obtained for the output beam.

Stability criterion for longitudinal plasma waves in a magnetic field

The dispersion equation of Cauchy integral type for longitudinal plasma oscillations in a magnetic field is for the first time exactly derived, in order to obtain the general instability criterion for magnetoplasma oscillations, on the basis of Vlasovs collision-free kinetic equation for arbitrary velocity distributions. The motion of the ions is easily taken into account by replacing Φ(k,v) by -(k,v) + +(k,v)m-/m+. The terms important for the drift instability are provided. The first two terms correspond to the dispersion relation either for the case of strong magnetic field approximation or for the case of grazing angle propagation. The third term contributes to the drift instability in the case of wave propagation at an appreciable angle to a finite magnetic field. The fourth and higher order terms give rise to the instability due to anistropic velocity distributions. The criterion for plasma instability in a magnetic field is obtained using potential theory.

Use of a gated counting method for radiation monitoring at a 45-MeV electron LINAC facility.

A fixed-point radiation monitoring system based on the gated counting method, which was previously reported by us, was constructed for a 45-MeV electron LINAC facility. It was tested under different beam intensities of the accelerator both at the current and repetition rates. It showed excellent dynamic response (from 2.5 X 10(-11) to 1.0 X 10(-8) Sv h-1) to the intensity variation of the radiation source. It was demonstrated that the system was very useful in monitoring an extremely low-level radiation from a pulsed source.