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Current distribution on the electrodes of a conventional MPD arcjet without external magnetic field was calculated based on induction equation, with the assumption that the magnetic Reynolds number is small. The calculated result, which showed the influence of tensor conductivity, coincided fairly well with the corresponding experimental one. It was seen, however, that the current density near the cathode tip in experiment had a larger value than that in calculation. This discrepancy was explained tentatively as being the result of the occurrence of cathode spots. It is also suggested in this paper that the unfavorable current concentration at the cathode base can be suppressed by using a specially devised divided cathode.

In electric arcs, there generally exists a considerable streaming of plasma caused by Lorentz forces generated by self-magnetic fields. The method of measurement of such streaming velocity is described. The arc used is a d-c thermal arc of 105 amp in argon at atmospheric pressure. The temperature of the arc was measured by a spectroscopic method and by a thermocouple, and a temperature distribution ranging from 16,000 to 1500 deg K was obtained. The streaming velocity was evaluated by measurement of the drag of a small plate swept across the arc, using the result of the temperature measurement, the drag coefficient of the plate, and the calculated density and viscosity coefficient of the plasma. At a section 2 mm from the cathode, the evaluated stream velocity was 135 m/sec at the center and 25 m/sec at the edge of the arc column from cathode to anode. The error in measured temperature is estimated at less than 10%, and the error in the measured stream velocity is considered to be less than 17.5%, excluding the error due to some change of the arc discharge caused by inserting the drag measuring plate. (auth)

The values of the viscosity and the thermal conductivity of partially ionized argon plasmas were obtained by investigating the decay of the temperature and the stream velocity distribution in an argon plasma jet at atmospheric pressure. The obtained results agree fairly well with the values calculated using the simple kinetic theory, and the influence of the ionization could be noticed in the results. This report includes the discussion on the thermal equilibrium of the plasma jet used. HE transport properties of high-temperature gases have been required with more practical application of them, although at present these cannot be obtained with good accuracy. This is especially true in the case of ionized or dissociated gases, because of difficulty of direct experimental measurements. Some experimental studies on transport properties of partially ionized plasmas have been reported, mainly on electrical conductivity.1"5 The measurements of the viscosity and the thermal conductivity in dissociated or ionized high-temperature gases at atmospheric pressure have been performed by using electric arcs.6"10 Wienecke6 obtained the thermal conductivity of air with 30% carbon impurity up to 10,000° K by investigating the cooling process of an arc which was observed after its current was cut off. Burhorn7 performed the measurement of the thermal conductivity of N 2 up to 13,000° K3 using the energy balance equation holding in an axially symmetric arc. Maecker8 measured the thermal conductivity of N2 up to 16,000° K by the same method as Burhorn's, but in detail, and obtained a good agreement with the values calculated by the simple kinetic theory. Knopp and Cambel9 measured the thermal conductivity of argon for the temperature range of 8500° to 12,000°K using an electric arc in a confined tube; and the obtained data were in good agreement with theoretically predicted results. Ahlborn and Wienecke10 measured the viscosity of air with 30% carbon impurity up to 10;000°K, using the momentum balance equation in a carbon arc in which the velocity distributions are known. We conducted the measurements of the viscosity and the thermal conductivity of partially ionized argon plasmas at atmospheric pressure, with the use of a plasma jet in which the thermal equilibrium is realized, as described later. The temperature distributions in the plasma jet were obtained by a spectroscopic method and a thermocouple. The axial velocity distributions were obtained by the drag method.11 The knowledge of the decay of the temperature and axial velocity distribution in the plasma jet permits the viscosity and the thermal conductivity to be obtained numerically, using the equations of continuity, momentum, and energy. The values of the viscosity and the thermal conductivity thus obtained were compared with the theoretical values as described below; and the influence of the ionization on their values was investigated. Theoretical studies on transport properties have been reported by some investigators; in these studies the rigorous kinetic theory of Chapman and Enskog12 is generally accepted as the base. In the present paper, the viscosity and the thermal conductivity were calculated by using the simple kinetic theory, considering partially ionized argon plasmas to be mixed gases of atoms, ions, and electrons.13 Besides, the values of the viscosity in partially ionized argon plasmas were calculated by means of the rigorous method for binary mixtures (atom and ion in this case), shown in Ref. 14. For reference, the values of the viscosity and the thermal conductivity in fully ionized argon plasmas were also calculated according to Refs. 15 and 16, respectively. These calculated values were compared with experimental results.

The heat input rate to wires in a partially ionized atmospheric pressure argon plasma (the degree of ionization is 75% at maximum), of which temperature and stream velocity are known, was measured with an estimated accuracy of ±8%. The thermodynamic and transport properties of atmospheric pressure argon at temperatures below 20,000 °K were calculated taking into consideration the effect of ionization. It was found that the incompressible empirical equations of heat and mass transfer are available for the estimation of the heat input rate in such a high temperature case. It was also shown by means of probe measurements that the boundary layers in the case of our experiments are near the frozen state and it is probable that the temperature of electrons is higher than that of atoms or ions in the boundary layers.