Naoyuki Kayukawa

High performance tokamak experiments with a ferritic steel wall on JFT-2M

Compatibility between the plasma and low activation ferritic steel, which is a candidate material for fusion demonstration reactors, has been investigated step by step in the JFT-2M tokamak. We have entered the third stage of the Advanced Material Tokamak EXperiment (AMTEX), where the inside of the vacuum vessel wall is completely covered with ferritic steel plates ferritic inside wall (FIW). The effects of a FIW on the plasma production, impurity release, the operation region, and H-mode characteristics have been investigated. No negative effect has been observed up to now. A high normalized beta plasma of βN ~ 3, having both an internal transport barrier and a steady H-mode edge was obtained. A remarkable reduction in ripple trapped loss from 0.26 MW m−2 (without ferritic steel) to less than 0.01 MW m−2 was demonstrated by the optimization of the thickness profile of FIW. A code to calculate fast ion losses, taking into account the full three-dimensional magnetic structure was developed, and values obtained using the code showed good agreement with experimental results. Thus, encouraging results are obtained for the use of this material in the demo-reactor.

Comparisons of MHD topping combined power generation systems

The efficiencies of six MHD topping combined power generation systems and one gas turbine topping combined system driven by different combinations of fuel and oxidant supply schematics were compared and classified on the bases of overall chemical reaction models for the combustion and gasification processes. The primary fuel was carbon that modeled a coal. The fuel types considered were coal and coal-synthesized gases which were provided by either conventional top gasification or by the tail gasification process. The oxidant was either pure oxygen, oxygen enriched air or air. In the MHD topping cases, the oxidant was preheated to each appropriate temperature. The enthalpy extraction of the corresponding power generation units in the topping and bottoming systems and the temperatures at the inlets of regenerators as well as at the stacks were assumed to be identical in all cases, except the inlet temperatures at the recuperative air heaters and the steam generators. We showed that the tail gasification system with an MHD topping and a combined gas turbine and steam turbine bottoming exhibited the highest plant efficiency insofar as it was based on the state-of-the-art technology of the power generation units and the heat exchanger.

Advanced Coal Power Cycle with a Stand-Alone Magnetohydrodynamic Generator

Ar egenerative and recirculation-type coal power system is proposed that works at high efficiencies with a stand-alone magnetohydrodynamic (MHD) generator under complete CO2 liquefaction. The open-cycle MHD generator is uniquely suited for the proposed cycle because combustion temperatures far exceed the working limits of conventional energy conversion devices due to both high fractional energy recirculation and oxygen combustion required for an efficient CO2 liquefaction process. The MHD exhaust heat is regenerated sequentially through the following three processes: thermochemical coal gasification, high-temperature syngas preheating, and an iodine‐ sulphur water splitting process. The mass and energy balances in each elementary process are calculated on the basis of Gibbs’ energy minimization principle. It is shown that the attainable system efficiency is much higher than either a coal gasification gas turbine combined cycle or a direct coal-fired MHD combined counterpart under the same evaluation criteria.

Behaviour of compact toroid injected into an external magnetic field

The interactions of a compact toroid (CT) plasma with an external magnetic field and a tokamak plasma have been studied experimentally on the FACT and JFT-2M devices. Fast framing camera and soft X ray emission profile measurements indicate shift and/or reflection motions of the CT plasma. New electrostatic probe measurements indicate that the CT plasma reaches at least up to the separatrix for discharges with toroidal field strengths of 1.0-1.4 T and that there exists a trailing plasma behind the CT. A large amplitude fluctuation on the ion saturation current and magnetic coil signals is observed. Power spectrum analysis suggests that this fluctuation is related to magnetic reconnection between the CT plasmoid and the toroidal field. The CT, including much of the trailing plasma, may be able to move across the external magnetic field more easily in the drift region of the injector owing to the Hall effect.

New Fossil Power Systems and the Role of Open-Cycle Magnetohydrodynamics Generators

Two scenarios for achieving CO 2 -free fossil fuel utilization in electric power systems are proposed, and the role of the open-cycle magnetohydrodynamics (MHD) power generation is discussed, taking into account the current trends of power generation systems and fossil fuel utilization. It is emphasized that the oxygen combustion of synthetic fuels, synthesis of primary fuels with exhaust gases and heat with additional steam, and separation of carbon dioxide from a syngas mixture should be performed in the central power stations to provide concentrated CO 2 recovery and hydrogen supply capability for dispersed-type power units. It is shown that MHD power generation driven by plasmas from oxygen-fired synthetic fuel might be the only possible candidate for a topping system in the ultimate base-load power station with the highest efficiency. Four models of central power generation systems were considered on the basis of the presumably attainable performance of the components, and the effects of the proposed scenarios were evaluated in terms of power generation efficiencies with the assumed fractional dependence on the dispersed-type power systems.

Electrical characteristics of an MHD generator with a transversally shaped configuration of magnetic induction

Electrical characteristics of a Faraday-type MHD generator with a transversally shaped field configuration (SFC) of magnetic induction were investigated experimentally by using shock heated plasma. The magnetic induction was sharply reduced near electrodes in order to minimize the electrical losses caused by the Hall effect and the conductivity nonuniformity in the boundary layer. The performance of the proposed generator was experimentally compared with that of the conventional type with a uniform field configuration. It was shown that the apparent conductivity, the output power, and the internal resistance were markedly improved in the SFC design, namely, by a factor of from about 1.5 to 2.0. The experimental characteristics agreed qualitatively with results of three-dimensional computer simulations. A possible arrangement of the superconducting coil for the generation of the SFC for a full-scale MHD generator channel was also proposed.

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.

High-temperature coal-syngas plasma characteristics for advanced MHD power generation

Properties of magnetohydrodynamic (MHD) plasma based on syngas (CO, H/sub 2/) combustion products were investigated experimentally with shock tube facility. The experiments were carried out under various MHD generator load and shock tube operation conditions. Important characteristics of syngas plasma such as temperature, electric field, conductivity, and total output power were directly measured and evaluated. Special attention was paid to the influence of syngas composition (CO:H/sub 2/:O/sub 2/ ratio). The results show that syngas combustion can provide high plasma ionization and attainable plasma electrical conductivity has an order of 60-80 S/m at gas temperature 3100-3300 K.

MHD/GAS TURBINE/STEAM TURBINE TRIPLE COMBINED CYCLE WITH THERMOCHEMICAL HEAT RECOVERY

An MHD/Gas/Steam combined cycle driven by coal gasified gas were studied where the gasification heat was supplied primarily from the MHD exhaust. As the most influential component, the synthetic gasoxygen fired MHD generator was investigated in detail. Without considering heat losses and electrical consumption, a 65 % plant thermal efficienciy was obtained with 25 % MHD enthalpy extraction and 45 % synthetic fuel partition to the MHD cycle. With inclusion of heat losses and power consumption, a 52.1 % efficiency was still demonstrated for a 1000 MWth scale MHD thermal input. The flow in the MHD channel was highly interactive with the magnetic field. The channel length and the volume required for given pressure drop were considerably reduced in comparison with those of the direct coal fired channel. More than 50 MWe/m3 power density could be attained under the wall stresses well below the critical values. We showed that the present cycle surpassed the direct coal fired MHD/ Steam conbination with respect to the efficiency and the C02 emission consuming the same amount of coal.

Comparative studies of advanced MHD topping power generation systems

Efficiencies of four different types of MHD topping combined systems were compared where the topping units were the MHD generator and a thermochemical coal converter. The bottoming system was either combined gas and steam turbine units, a steam injection-type gas turbine, a steam turbine unit or a steam turbine coupled with a biomass unit. We also considered an IGCC system with conventional gasification schematics as a reference case. We showed that the system combined with the steam turbine and biomass units exhibited the highest efficiency of over 60% with presumably attainable MHD unit efficiencies although it is workable only under sunlight and its power scale may be limited by the pond area of the biomass plant. The present results emphasize capabilities of an advanced power generation system with extremely low environmental impacts and high efficiencies among those of the so far proposed fossil fuel-fired power plants on the basis of the MHD and the state-of-the-art heat recovery technologies.