M Numano

Comparison of Langmuir probe and spectroscopic electron temperature measurements

Deals with an experimental confirmation of the deviation from LTE in a low density argon plasma and of the applicability of the theory on the deviation from LTE developed by Griem. The excitation temperature determined spectroscopically using relative intensities of the resonance lines 4000-7000 AA of argon atoms was compared with the electron temperature measured by a conventional Langmuir probe. As a result it was found that the excitation temperature was 1000- 1500 degrees C higher than the electron temperature and that the difference between them increased along the radius of the plasma stream. It implies that the plasma was not in LTE. In fact the excitation temperature determined from relative populations of the 5p states of the argon atoms was found to agree quite well with electron temperature across the plasma stream.

Application of a von Mises transformation to a problem of non-linear one-dimensional electron plasma oscillations.

A von Mises transformation is applied to a non-linear boundary-value problem on electrostatic plasma oscillations. The results are found in good agreement with those of Davidson et al. (1968).

Performance Characteristics of an MHD Power Generator with Seeding Plane and Staggered Electrodes

This paper deals with a theoretical investigation on the influences of the seeding position and the electrode staggering on the electrical performance characteristics of a Faraday-type MHD power generator. The analysis was made by means of conformal mapping techniques. The results revealed the following: 1. The influences in question can be expressed by a parameter determined uniquely by the generator geometry. 2. The internal resistance of the generator is independent of the direction of the electrode staggering. 3. There exists a value of stagger at which the internal resistance is minimized for a finite seeding aspect ratio. 4. The electric current concentration on the electrode edge can be attenuated by suitably staggering the electrode. 5. Generators with a single electrode pair and those with segmented electrodes have quite similar current density profile on the electrode surfaces, but rather different distribution on the generator center line.

Relaxation effect on sound propagation in partially ionized gases

The effect of ionization-recombination processes on sound propagation in a partially ionized gas was investigated by employing the fluid model under the assumption that the ionization-recombination frequency is much lower than the collision frequency of heavy particles, and the sound speed and the absorption coefficient were obtained as functions of frequency. It is found that for low frequencies small disturbances propagate with the equilibrium sound speed and that the sound speed increases monotonically with frequency and approaches the frozen sound speed for sufficiently high frequencies. It is found also that the sound is absorbed as it propagates in the medium and the absorption coefficient increases monotonically with the frequency.

Determination of Stability Domain of Reactor with Single Temperature and Prompt Power Coefficient

Determination of the stability domain was studied for nonlinear reactor problems. An approximate stability boundary was determined analytically in the state space by observing the nature of trajectories and with the help of isoclines. This approximation can be improved to any higher degree. The method was applied successfully to the problem of one-point, effective neutron-lifetime reactor-model with linear temperature and power coefficients and cooled by Newtons law, and to a modified system with nonlinear feedback characteristics. The former example is a well-investigated test case, and the present method resulted in a stability domain larger than those determined by most other methods except numerical determination using computer.

Turbulence effect on Ohm's law in partially ionized plasmas

Investigates the effect of nonuniformity on electric current flow in partially ionized plasmas. An Ohms law for a nonuniform plasma was derived, from which Rosas equation (1968) is obtained as a special case. Making use of this new Ohms law, the effective electrical conductivity and Hall coefficient were determined for isotropically turbulent plasmas. They were found to be in good agreement with the results obtained previously.

Saha and temperature relaxation approximations for the study of ionization instability in partially ionized plasma

The growth rates for the ionization instability obtained using the Saha and temperature relaxation approximations are compared with those obtained from an exact treatment, and the requirements for validity of these two approximations are obtained analytically. For the range of plasma parameters pertinent to MHD power generation it is found that the Saha approximation is valid for relatively high electron temperature, while it becomes inapplicable as the electron temperature is decreased. On the other hand, the temperature relaxation approximation is accurate over a wide range of electron temperature. The marginal condition for the ionization instability is correctly obtained from both approximations.

Experimental Study of the Relaxation Phenomena in Non-Equilibrium MHD Generator Duct

The non-equilibrium electrical conductivity and the relaxation of electron density in seeded plasma for MHD power generators were studied experimentally. The experiments were performed with use made of potassium seeded argon plasma (A+0.14%K) at 1,800°2,000°K, flowing in a rectangular duct at constant velocity (about 240m/sec) under atmospheric pressure. The dependence of the electrical conductivity on the electric current density was found to agree well with theoretical prediction based on the two-temperature model, if a value of 40 was chosen for the collision loss parameter. The effect of the radiative energy loss of potassium atoms was not significant in the present experiments. Furthermore, it was found that the relaxation of the electron density can be well expressed by the recombination coefficient for the electronic three-body recombination processes, and that the relaxation time is about 4 × 104 sec for the present experimental conditions.

A THEORETICAL STUDY OF MHD POWER GENERATION. III. THE LIFT OF ELECTRON TEMPERATURE

This paper deals with the lift of the electron temperature in the electromagnetic field. In view of the small ionization degree in the working gas of MHD power generation, the collision of charged ...

A Theoretical Study of MHD Power Generation, (II): The Potential Drop Near the Electrodes

The electric potential drop near the electrode surfaces in MHD power generators is studied theoretically by considering a simple model, in which the current flows in the direction normal to the electrode surfaces. In order to simplify the situation so as to permit analytic solution, the idea of a “boundary layer” near the electrodes is introduced, and the problem is treated entirely macroscopically, wherein the following assumptions are made: 1. The electrical conductivity is constant. 2. The Hall effect and the induced magnetic field can be neglected. 3. The behavior of the flow in the boundary layer may be described by equations for laminar flow. 4. The temperature variation in the boundary layer perpendicular to the electrode surfaces may be neglected. The theory predicts that the magnitude of the electric potential drop near the electrode is of the order of 10 V in typical MHD power generators.