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This paper discusses the stress dependence of magnetizing properties in non-oriented electrical steel sheets (NO). Compression stresses deteriorate the magnetic properties at low flux density, but improve them at high flux density, where magnetization rotations are induced. Tensile stresses reduce magnetizing fields at low flux density, but increase them at high flux density. The stress dependence of NO is affected by the exciting direction, as the rolling direction of NO is easy to magnetize and sensitive to stresses. High-grade types of NO (50A290, etc), which have high Si content and large crystalline grains, are more sensitive to stresses than low grades (50A1300, etc), and the magnetizing fields of high grades at high compression are higher than those of low grades. This stress dependence may depend on magnetization behaviors (domain wall displacement and magnetization rotation) and magnetostriction. Domain wall displacement mainly occurs at lower flux density, and in this case tensile stresses improve magnetic properties and compression deteriorate them because magnetic domains orient the magnetization to and λ100 is positive. However, magnetizations rotate to exciting directions at high flux densities, with the result that the component of magnetization is induced, and in this case compression improves the magnetizing properties, because λ111 is negative, whereas tensile stress deteriorates them. Therefore, stress dependences may be modeled by magnetization behaviors and magnetostriction, and analysis of the magnetic properties using this model of stress dependence may improve NO steels and their applications.

Experimental results of nonequilibrium plasma magnetohydrodynamic (MHD) power generation from the Fuji-1 blowdown facility are presented. The Fuji-1 experiments have been conducted since 1983, and the disk-shaped MHD generators called Disk-F3a, F3r, and F4 have been tested during the last decade. In the experiment with the newest Disk-F4 generator, which was designed based on the results of previous experiments with the Disk-F3a and F3r generators, an output power of 506 kW and an enthalpy extraction ratio of 18.4% for thermal input of 2.75 MW were simultaneously obtained. During the experiment, however, the deposition of seed material on the electrodes and the insulator walls was revealed, and large amount of impurity (water vapor) contamination in the working gas was detected. In the last experiment the stainless-steel-coated anodes were used instead of copper anodes to prevent the seed material from depositing on the generator walls, and the impurity contamination was reduced by increasing the bottom temperature of the heat exchanger. Consequently, an output power of 544 kW for thermal input of 3.38 MW and an enthalpy extraction ratio of 18.9% for thermal input of 2.17 MW were successfully demonstrated. Each value is the highest among those achieved with the Fuji-1 facility.

The performance of a nonequilibrium disk magnetohydrodynamic (MHD) generator under subsonic flow condition is examined with time-dependent /spl tau/-/spl theta/-z three-dimensional numerical simulation for the first time. The uniform plasma structure and proper fluid flow are realized for the optimal working condition. For low-load resistance, however, the flow chokes at the throat, and shock waves and boundary layer separation are observed in the generator channel. For high-load resistance, on the other hand, the subsonic flow is maintained, although the boundary layer becomes considerably thick. When the plasma with low electron temperature flows into the generator, ionization instability takes place, which markedly reduces the enthalpy extraction ratio and isentropic efficiency. This suggests that some way to raise the electron temperature in the upstream region, for example, a pre-ionization, is needed.

Three-dimensional numerical simulations have been carried out in order to explain the experimental results with a shock-tube-driven disk magnetohydrodynamics (MHD) generator with inlet swirl for the first time. The numerical results agree well with the experimental results especially in the enthalpy extraction ratio. The isentropic efficiency obtained numerically is higher than that in the experiment, for seed fractions lower than the optimum value. There may exist some additional mechanism causing a total pressure loss which cannot be, included in the present numerical model. The radial component of Mach number becomes less than unity for high seed fractions. This decrease in Mach number is not so steep but moderate, and seems to be different from that attributed to a shock wave observed in a fluid flow without MHD interaction. The plasma structure is almost uniform in the /spl theta/ direction near the optimum conditions. Under the condition far from the optimum value, however, a nonuniform and unsteady plasma structure owing to the partial ionization of seed material is observed.

The effects of diffuser shape and back pressure on the performance of closed-cycle disk MHD generators are investigated with two-dimensional numerical simulations taking account of the boundary layer. The enthalpy extraction ratio decreases and fluctuates periodically with increase in the back pressure. The amplitude of power output fluctuation and the period depend on the volume of the inverse flow region. For the reduced height diffuser, the inverse flow region is suppressed and the fluctuation becomes smaller than that for the constant height diffuser. When operated with a back pressure lower than an optimum value, the diffuser does not work because of reacceleration in the diffuser. For the higher back pressure, on the contrary, the inverse flow region propagates into the MHD channel, then the enthalpy extraction ratio is reduced and the Mach number at the exit of the MHD channel becomes lower than unity. For the optimum back pressure, high enthalpy extraction ratio is achieved and the adiabatic efficiency at the diffuser exit is decreased by several percent from that evaluated at the MHD channel exit. © 2000 Scripta Technica, Electr Eng Jpn, 133(2): 11–19, 2000

Recent experimental results of closed cycle MHD electrical power generation with the “Fuji-1” blow-down facility are presented. In the experiment with Disk-F4 MHD generator, which was conducted with a modified seed injection system in 1997, an enthalpy extraction ratio of 18.4% was successfully demonstrated with a large output power of 506 kW. This enthalpy extraction ratio is the highest among those achieved with the Fuji-1 facility. The experimental results also revealed the electrical characteristics of the generator installed in the blow-down facility. The decline in the output power and its recovery were observed at the early stage of the power generation run. This fact could be attributed to the attachment of seed material to the generator walls and to its detachment, related to the relatively slow rise in temperature on the wall surface. It was verified for the first time in the Fuji-1 experiment that the reduction of impurity contamination resulted in improvement in the generator performance.

By applying a radio-frequency (RF) electromagnetic field, the feasibility of improvement in the performance of a nonequilibrium disk-shaped magnetohydrodynamic (MHD) generator suffering from water vapor contamination in the working gas is investigated with r-/spl theta/ two-dimensional numerical simulations. Attention is paid to the relation between the behavior of MHD plasma in the presence of the RF electric field and the generator performance. The water contamination causes the strongly nonuniform and unsteady plasma, and deteriorates its performance. The fluctuations of the electron temperature and of the ionization degree of seed atoms are found to be suppressed by applying the RF electric field. As a result, the enthalpy extraction ratio and the isentropic efficiency of the generator improve. The ratio of the required additional joule heating by the RF electric field to the thermal input to the generator for the stabilization of the plasma and the improvement in the performance is estimated to be about 0.9%.

Cooling performance of superfluid helium (HeII) channels, separated by a porous spacer, has been experimentally investigated. The test channels were formed in parallel by FRP block. A spacer was used to separate two channels of the same shape. Both ends of the channels were kept open to an atmospherically pressurized HeII bath. Two types of spacers were examined—(1) FRP spacer, (2) the central portion of the FRP spacer was replaced by a porous spacer. The mean pore diameter was 1 μ m. The λ transition heat flux, which is defined as the heat flux necessary to raise the helium temperature in the channel to the λ transition temperature, T λ , increases remarkably when the porous spacer is used instead of the FRP spacer. It is also found that the use of porous spacers between HeII channels is effective to suppress a steep temperature rise in the heated channel because HeII flow is induced in the heated channel by a fountain effect.

Three-dimensional nonuniform plasmas and boundary layers have been studied numerically under an MHD interaction. The nonuniform plasma of "streamer" owing to weak ionization of seed material has a spiral structure in the r-/spl theta/ plane, and the plasma becomes almost uniform between the walls in the r-z plane. This structure is almost the same as that in our previous paper (1997), where the gas (heavy particle) properties are assumed to be invariant and steady. In addition to the streamer, the nonuniform plasma of "domain" owing to weak ionization of noble gas is revealed. The domain has the structure perpendicular to the streamer. In a strong MHD interaction case, the static pressure considerably increases in the upstream region of a generation channel, and the pseudo-shock waves appear in the generator, but the plasma is almost uniform along the /spl theta/ direction. The boundary layer in the strong MHD interaction is considerably thick, and in the broad region near the wall the Hall current flows reversely. In the weak MHD interaction case, the plasma forms a nonuniform structure along the /spl theta/ direction, and the Hall current does not always flow in the opposite direction even on the insulator wall since the azimuthal electric field is not zero.

The three-dimensional (3-D) structure and behavior of nonequilibrium alkali metal seeded plasma in a supersonic disk closed cycle MHD (CCMHD) generator are simulated numerically. The simulation reveals the unsteady 3-D nonuniform plasma caused by the ionization instability. The plasma with low electron temperatures of /spl sim/5000 K, corresponding to the fully ionized seed plasma, has spiral structure in the r-/spl theta/ plane, and looks like a straight pillar between walls in r-z plane. The plasma flows repeatedly downstream in the generator, changing the shape unsteadily. For high load resistance, the nonuniform region is contracted near the inlet of the generator, and the plasma becomes steady and three-dimensionally uniform. The nonuniform structure does not appear in the regions between the faced anodes and between the faced cathodes, although the electron temperature is relatively low (/spl sim/3000 K) and the plasma is under the regime of a weakly ionized seed.

The formation and evolution of the ionization nonuniformities from initial disturbances of finite amplitude in the nonequilibrium Ar-Cs plasma in a disk magnetohydrodynamic (MHD) generator is studied by the numerical simulation, The simulations are carried out in the wide interval of electron temperatures corresponding to the region at which the seed partially ionizes, the region of the linear plasma stability at the fully ionized seed, and the region of the instability corresponding to the partial ionization of Ar at high electron temperatures. Initial disturbances of finite amplitude in electron temperature and density are introduced at the time t=0 into the homogeneous plasma distribution, and the critical amplitudes determining the development of the instability are calculated. The initial disturbances are constructed using random functions with different spatial scales, The results are compared with the calculation of the critical amplitudes from the nonlinear theory of the plane ionization waves, It is found that at electron temperatures lower than 5500 K, the temperature dependence of the critical amplitudes and the structure of the nonlinear waves agree well with the nonlinear theory, In the electron temperature region corresponding to the partial ionization of the noble gas (T/sub e/>5500 K), the finite ionization rate of argon atoms is essential for analysis of the instability, In this region the margin of the plasma stability is wider than it is predicted by the nonlinear theory, The nonuniformity in the argon ion number density plays the dominating role in the instability development at high electron temperatures (T/sub e/>5500 K) in comparison with the nonuniformity in T/sub e/ in the initial disturbances,.

Structures of nonequilibrium inductively coupled plasmas with cesium metal vapor ionization in argon gas are revealed experimentally and are compared with ones from two-dimensional numerical simulations. The main object of the present paper is to clarify the behavior of the plasma in which cesium atoms as seed atoms are completely ionized, and the ionization of the argon gas as a mother gas is negligible, that is, the fully ionized seed (FIS) plasma, produced by the inductive radio-frequency electric fields. The plasmas are generated in a cylindrical quartz discharge tube around which a four-turn induction coil is wound, under the conditions of currents of

Nonequilibrium plasmas with cesium metal vapor ionization in helium and argon gases at moderate pressures are excited with microwave power. The structures and behaviour of the seeded plasmas are experimentally examined, particularly under the condition of Full seed (cesium atoms) ionization. By cesium seeding, the minimum power sustaining the plasma is reduced markedly, and both a broad plasma observed in pure helium and unsteady filament-like plasmas in pure argon change to the steady and broad plasma locating close to the inner surface of a discharge tube, it is revealed from the electron temperature measurements that the plasma can be in the regime of full seed ionization for suitable microwave powers, where the electron density is kept almost constant. The thickness of the fully ionized seed (FIS) plasma decreases with increasing the mole fraction of cesium vapor, and is almost independent of noble gas pressure. The thickness almost coincides with the skin depth determined from the electrical conductivity almost uniform in the FIS plasma. These facts suggest that the FIS plasma will be easily produced and maintained as long as the microwave power is consumed to the electron heating.

Operational characteristics of a fountain effect pump in a HeII flow loop have been experimentally investigated. Relations between a HeII mass flow rate in the loop and a supplied heat to the pump were measured with different dimensions of the porous plug and the tubes which make up the loop. It is confirmed that the supplied heat can be used effectively to drive HeII when appropriate sizes of the plug and the tubes at the inlet and outlet of the pump are chosen. The tube at the inlet of the plug is required to remove most of the supplied heat and to suppress an increase of HeII temperature at the inlet and outlet of the plug. The tube at the outlet of the plug is required to restrict the heat leakage to the downstream of the flow.

Nonequilibrium inductively coupled plasma (ICP) where cesium metal atoms contained in argon gas as a seed material are dominantly ionized is investigated with two-dimensional (2-D) numerical calculations which are based on a fully time-dependent (FTD) model and sinusoidal approximation (SA) model. Calculation results with the FTD model indicate that the amplitude of electron temperature oscillation over one radio frequency cycle is below about 120 K for the mean value of about 5600 K, and that of the electron number density is negligible due to its long relaxation time. Results with the SA model coincide with that with the FTD model, and it is valid to predict the plasma properties with the SA model. Under the suitable operating conditions, the region where electron number density is kept constant is formed and extended in the ICP, since the electron temperature ranging from 4000 to 6000 K is realized, and cesium atoms are fully ionized while the ionization of argon atoms is not significant. Since no current is induced at the center axis of ICP, the density profile around the axis is almost determined by the diffusion of electrons from the region of full seed ionization.

Operational characteristics of He II loop flow driven by a fountain effect pump under steady state condition have been experimentally investigated for different thermal and flow impedances. It is confirmed that an appropriate length of vortex tube, which restricts the heat leak flowing downstream of the pump, is required to utilize the supplied heat and to drive the pump effectively. The He II mass flow rate in the loop does not depend upon the length of the vortex tube provided the vortex tube is longer than the appropriate length in the present experiment. However, the pressure and temperature differences between the outlet and inlet of the pump increase with increase in length of the vortex tube.

The Saha equilibrium approximation and the temperature relaxation approximation to the MHD equations are investigated with regard to the analysis of the formation of nonlinear ionization non-uniformities and their evolution in a non- equilibrium MHD plasma. An analysis of characteristic relaxation times under typical plasma parameters is carried out to verify these approximations. Characteristic space scales of electron thermal conductivity and radiation are evaluated. These space scales determine the characteristic width of nonlinear ionization wave fronts, and are important for the application of numerical simulations.

Two dimensional calculations were carried out to clarify the behavior of boundary layer and its effects on performance of closed cycle MHD (CCMHD) generator and to investigate the relation between enthalpy extraction ratio and adiabatic efficiency. Calculation results suggest that the large Lorentz force causes propagation and separation of boundary layer where reverse current flows, because of small electromotive force. For large load resistance boundary layer becomes very thick and the eddy current arises in broad region. The push work of working gas against Lorentz force is effectively converted into electric energy under the condition at which the Lorentz force decelerates the working gas to Mach number in the range between 1.0 and 1.5 in this case of the generator. Stagnation pressure loss increases with load resistance until enthalpy extraction ratio takes maximum value. The entropy production due to Joule heating and viscosity increases with load resistance. The difference between the load resistances for which the enthalpy extraction ratio and the adiabatic efficiency take maximum value can be explained with the entropy production of Joule heating and viscosity. >

Experimental and numerical investigations have been carried out on the heat transport characteristics in a channel where atmospherically pressurized He II coexists with He I. The channel has a rectangular cross-section and both ends are open to the bath. One of the side walls of the channel is heated uniformly. The channel is placed vertically or horizontally in the bath. The experimental results are analysed by two-dimensional time-dependent numerical calculations. An explicit finite element scheme is applied to the two-fluid equations which include the Gorter-Mellink mutual friction term. It is found that the applied heat is transported by one-dimensional internal convection through the channel filled with single phase He II. Once He I is generated in the channel, however, two-dimensional flow occurs due to natural convection and this influences the transport of heat.

Recent results of power generation experiments with an improved heat exchanger system in the FUJI-1 facility were described. One of the main purposes was to study the effect of working gas temperature on generator performance. The results with argon working gas showed that the gas temperature of 1850 K is enough to eliminate the effect of inlet relaxation under the present experimental conditions and that gas temperature does not greatly affect the output performance so long as the inlet relaxation is not significant. The radial component of velocity was successfully measured with high time resolution by means of the cross-correlation method. The effect of seed fraction on the measured velocity was discussed. For the case of helium working gas, the voltage drop owing to an inlet relaxation was remarkably decreased, and improvement in both output power and enthalpy extraction can be observed by the increase of gas temperature. The voltage drop still existed at the inlet of the channel, and therefore, higher gas temperature and higher seed fraction are required in order to achieve higher generator performance.

The absorption cross section of the B1∏u−X1Σ+g band system (610–720 nm) of K2 has been investigated experimentally in K-Ar mixtures. Absorption spectra of the band system were measured at a gas temperature of 773 K and gas pressures from 10 to 1000 kPa. The number density of K was measured using the total absorption of the resonance lines and the number density of K2 was determined from the equilibrium relation. It has been found that the absorption coefficient of the band system is smoothed by collision broadening of the lines in the band system and becomes effectively constant at pressures greater than 200 kPa. The effect of the gas temperature on the absorption cross section is evaluated theoretically.

Nonequilibrium MHD plasma flow in a high-interaction disk-type MHD generator is examined by numerical simulations based on the two-temperature model equations. The simulations are performed for the generators driven by working gases: He-Cs and He-K. Homogeneous and inhomogeneous plasma behavior is observed with change of the load resistance, and it is found that the structures of the inhomogeneous plasma differ for different seed materials. The plasma structures associated with both the partial ionization instability and the magnetoacoustic instability are discussed for both plasmas. >

A design method for helium-driven MHD disk generator channels including boundary-layer behavior is proposed. In this method, the main flow in the channels is one-dimensionally treated, taking account of the concept of effective cross-sectional area of the channels. This effective area is determined by solving two-dimensional boundary-layer equations. Using this method, the generator channels on various scales are numerically designed under the condition of fully ionized seed. Furthermore, the scale effects of the boundary layer on the area ratio, heat loss and adiabatic efficiency of the generators are examined. It is found from this study that a generator having a thermal input of more than 100 MW is required to achieve high enthalpy extraction with high adiabatic efficiency (more than 65%).

A novel planar antenna employing a stretched structure and meshed material is proposed in order to reduce the weight drastically and experimental results in S-band are described. As a result, the developed planar array antenna has a weight of 300 g/m/sup 2/, one third that of a conventional one, and has good RF performance.

Experimental studies on closed cycle MHD power generation with “Fuji-1” blow-down facility at Tokyo Institute of Technology are presented. Recently, a new disk generator (Disk-F4) has been installed and a new seed injection system has been introduced from IVTAN (Institute of High Temperature in Russia). The design concept of the new generator channel is focused mainly on the reliability of high power generation. In the new seeding system, a melted seed material is pushed by a piston dozator, instead of gas-pressure-driven in the previous system. In the power generation experiments with the new components, the maximum power output of 502kW and the enthalpy extraction ratio of 16.7% have been obtained. These values at the present stage are lower than the maximum values previously achieved in the facility. However, the reproducible high power generation has been demonstrated with the new generator. The behavior of plasma and fluid under strong MHD interaction taking place in the generator channel is discussed.

Recent experimental results of closed cycle MHD electrical power generation with "Fuji-1" blow-down facility are presented. In the experiment with Disk-F4 MHD generator, which was conducted with a modified seed injection system in 1997, enthalpy extraction ratio of 18.4% was successfully demonstrated with a large output power of 506kW. This enthalpy extraction ratio is the highest among those achieved with the Fuji-1 facility. The experimental results also revealed the electrical characteristics of the generator installed in the blowdown facility. The decline in the output power and its recovery were observed at the early stage of the power generation run. This fact could be attributed to the attachment of seed material to the generator walls and to its detachment, related to the relatively slow rise in temperature on the wall surface. It was verified for the first time in the Fuji-1 experiment that the reduction of impurity contamination resulted in the improvement in the generator performance.

In the Fuji-1 blow-down experiments, asymmetric total pressure profiles across the channel height have been observed in the absence of the MHD interactions. It is known from observation that asymmetric total pressure profiles tend to be symmetric with the MHD interactions. Two-dimensional numerical simulations including the boundary layer have been carried out to investigate the hydrodynamic and plasmadynamic properties. In this studies, the simulation code is modified to investigate becomes asymmetric in the height direction due to some pseudo shock waves, and a large region of flow separation exists at downstream of the channel. It is also observed that the asymmetric flow in the absence of MHD effect tends to be symmetric with increasing MHD interaction. Three dimensional numerical simulation have been carried out for the flow field in the absence of the MHD effect, the properties of flow field in the disk channel have been discussed [2]. High enthalpy extraction of disk closed cycle the effects of back pressure on structures of flow MHD

A two-dimensional compressible turbulent boundary layer model is adopted to predict the boundary layer characteristics of the 100 MW thermal input supersonic disk MHD generator walls for helium and argon under various enthalpy extraction conditions. The results show that the boundary layer thickness increases downstream in the channel for both argon and helium, and for helium, there occurs a boundary layer separation under high enthalpy extraction conditions. A slow variation of the Faraday current is observed through the boundary layer, while the Hall current decreases sharply, and the direction of the Hall current gets reversed in the vicinity of the insulator wall at the channel downstream end. This effect is observed to be more prominent for helium than for argon. The percentage of pressure loss through friction is found to be more for argon than for helium, while the heat loss is observed to be more for helium than for argon.

The effects of ionization relaxation and ionization instability on the electrical discharge in a seeded noble gas have been studied experimentally. Experiments have been made in a simulated MHD channel in which current is applied to each of several electrode pairs with and without a magnetic field present. Experimental results have shown that unsteady current concentration in the ionization relaxation region and ionization instability induce a non-uniform and fluctuating discharge downstream. The effect of unsteady concentrated discharge in the relaxation region is reduced when current is increased. The ionization instability is also reduced when the seed becomes fully ionized. Experimental values of the effective electrical conductivity and Hall coefficient in the flow downstream have shown agreement with the values predicted by the theory for a large current.

Unsteady electrical discharges in a nonequilibrium disk MHD generator and its effects on the flowfield are studied theoretically. Numerical results obtained from time-dependent and one-dimensional MHD equations have shown a periodic motion of the discharge, which induces fluctuations of Hall current and flowfield. Repetitional frequency of the discharge becomes higher with increasing seed fraction and external load resistance. When Joule heating is large, the unsteady discharge becomes limited only near the anode, and a steady discharge dominates over the disk generator. 17 references.

The r-theta two-dimensional, time-dependent simulations of nonequilibrium plasma are carried out to develop a stable plasma with a fully ionized seed in a disk-type closed-cycle MHD power generation system. The working gases were Ar/K, Ar/Cs, He/K, and He/Cs. For all of the working gases considered, stable plasma with a fully ionized seed is obtained in nearly the entire generator, except in the relaxation region close to the anode. As the seed material, cesium produces better performance than potassium. Even when helium is used as the working gas instead of argon, it is expected that good performance can be obtained by suitably adjusting the gas conditions, magnetic field, and load resistance. 15 references.

Comparative studies of the performance of closed cycle disk MHD generators using argon, helium and an argon-helium mixture are performed under the concept of fully ionized seed. Calculations show that either pure argon or pure helium is desirable as an inert gas in closed cycle MHD generators compared to the mixture of argon and helium and that a typical MHD channel for helium becomes compact. In typical disk generators, it is found that partial load operation with high efficiency can be established, and that fluctuations of the seed fraction are permitted within the limits of about ±3% and ±6% for the disk generator using argon and helium as inert gases, respectively. Furthermore, it is shown that a stable plasma can be maintained for a wide range of gas temperature by adjusting the seed fraction.

Analyses of a high interaction closed cycle MHD generator have been performed to confirm the feasibility of the fully ionized seed concept. The results show that fully ionized seed can be realized in a full scale generator and that it has an advantage over partially ionized seed of higher adiabatic efficiency. In order to keep the plasma in a given generator stable, the results show that the seed fraction and the external load fluctuation must stay within ± 5% and ±3%, respectively. For a wider change in the external load we can also keep the plams stable if the change is so slow that we can adjust the magnetic field, the thermal input and the working gas pressure.

Design studies on superconducting magnets coupled with a full-scale (1000 MWth) closed-cycle disk MHD generator are described. Special attention is given to a hew supporting structure that can sustain a large electromagnetic force induced between the windings in Helmholtz-type magnets; and the feasibility of this structure is examined. It is shown that the magnet is expected to become considerably compact.

The realization of the stable plasma due to the fully ionized seed has been dynamically confirmed in a channel of the closed cycle disk generator by solving time-dependent MHD equations. The relaxation process is examined near the inlet of the disk generator. In the stable state, as the load resistance increases, the width of the relaxation region becomes narrower and, as a result, the uniformity of the plasma in a whole channel becomes better. The influences of the inlet conditions on changes of the relaxation region are also examined.

A new method for superfluid cooling has been developed in which a NbTi magnet is located in vacuum and cooled by conduction with the heat exchanger directly attached to the magnet. The cooling system was easy to operate and reached 1.8 K temperature in 30 s. The magnet was successfully energized up to 12.23 T, the limit value expected from l c ( B ) curve. An idea for the stabilization of the indirect cooled magnets has been proposed.

A degenerate parametric oscillator which is driven by a random current additionally applied to a sinusoidal pumping current is found to exhibit a new type of oscillatory‐to‐nonoscillatory transition. This noise‐induced phase transition has a different kind of critical behavior from that observed in usual phase transitions, that is, near the threshold the variance of the fluctuating output current remains constant, however, the critical slowing‐down does occur. A stochastic equation for the parametric oscillation which includes a random force multiplied by the amplitude itself is derived and the experimental results are fully accounted for in terms of that equation.

The high frequency conductivity of ferromagnetic semiconductor CdCr 2 Se 4 doped with 0.1 at.% Ga is measured as a function of temperature (4.2–320 K) in the frequency range from 0.5 MHz to 24 GHz. The remarkable frequency dispersion of conductivity σ(ω) is observed. The frequency dependence of σ(ω) is different in the temperature range above and below the Curie point ( T c = 130 K).

Experimental studies on closed cycle MHD power generation with "Fuji-1" blow-down facility at the Tokyo Institute of Technology are presented. Recently, a new disk generator (Disk-F4) has been installed and a new seed injection system has been introduced from IVTAN (Institute of High Temperature in Russia). The design concept of the new generator channel is focused mainly on the reliability of high power generation. The Mach number at the generator inlet and the thermal input are increased up to /spl sim/2.8 and /spl sim/3.0 MW, respectively. In the new seeding system, a melted seed material is pushed by a piston dozator, instead of being gas-pressure-driven as in the previous system. The controllability of seed fraction is markedly improved, and the large fluctuation as has been observed previously is diminished. In power generation experiments with these new components, a maximum power output of 502 kW and an enthalpy extraction ratio of 16.7% have been obtained. These values at the present stage are lower than the maximum values previously achieved in the facility. However, reliable high power generation can be expected with the new generator. The behavior of plasma and fluid under high MHD interaction taking place in the generator channel is also discussed.

We have observed a phase transition induced by external noise, using a parametric oscillator driven by a random current, additionally supplied to the sinusoidal pumping current.

The effects of externally induced small fluctuations in the input thermal energy and/or the seed fraction are examined using numerical simulations based on two-temperature MHD (magnetohydrodynamic) equation system. A quasi-one-dimensional approach is adopted for a disk generator. A generator with a high enthalpy extraction rate is considered, and its design parameters are set so that the full ionization of seed contained in the plasma is realized. The fluctuations in seed fraction and gas pressure influence the performance of a generator in several different ways. >