[en] Feasibility of commercial tokamak reactors is discussed. The range of cost of electricity (COE) by competitors of fusion is estimated and the target range of COE for the fusion reactors is proposed. It is shown that the high β advanced plasma mode will break through this COE target. As a possible path toward the cost competitive tokamak concepts, the reactor compact reversed shear tokamak (CREST), which is based on the high β plasma and super-heated steam cycle, is briefly reviewed

[en] The background field approach to non-Abelian gauge field theory in stochastic quantization is presented. We discuss on the bases of the Zwanziger type stochastic gauge fixing in which we need not introduce the Faddeev-Popov ghost field. We can choose the Zwanziger function, and resultingly the Langevin equation, to be manifestly covariant under the background gauge transformation. Due to the background gauge covariance, we can easily find a simple Ward identity by which the β-function calculation in stochastic quantization can be extremely simplified. We give the one loop result of the β-function which is equivalent to the normal one. We also give another β-function β_γ, which will give the relation between the energy scale and the fictitious time scale. (orig.)

[en] Beam driven steady state tokamaks of moderate size (R_o = 4.55 m) is analyzed by a full consistent beam current drive analysis code, which consistently includes MHD equilibrium, kink and ballooning stability analysis, bootstrap current, power balance and momentum balance calculations. It was found that this moderate size is sufficient to demonstrate the feasibility of steady state operation by the neutral beam current drive. The maximum Q value attains Q = 7∼9 with the fusion power P_f = 500∼800 MW and L-mode confinement is sufficient to sustain self consistent equilibria. The Q value is nearly doubled due to the bootstrap current and the T_i > T_e feature of beam driven tokamaks. The optimum beam energy is 1.0∼1.2 MeV and the toroidal rotation effects has been negligible. (author)

[en] A new MHD-equilibrium/current-drive analysis code was developed to analyse the high beta tokamak equilibria consistent with the beam driven current profiles. In this new code, the critical beta equilibrium, which is stable against the ballooning mode, the kink mode and the Mercier mode, is determined first using MHD equilibrium and stability analysis codes (EQLAUS/ERATO). Then, the current drive parameters and the plasma parameters, required to sustain this critical beta equilibrium, are determined by iterative calculations. The beam driven current profiles are evaluated by the Fokker-Planck calculations on individual flux surfaces, where the toroidal effects on the beam ion and plasma electron trajectories are considered. The pressure calculation takes into account the beam ion and fast alpha components. A peculiarity of our new method is that the obtained solution is not only consistent with the MHD equilibrium but also consistent with the critical beta limit conditions, in the current profile and the pressure profile. Using this new method, β ∼ 21 % bean and β ∼ 6 % D-type critical beta equilibria were scanned for various parameters; the major radius, magnetic field, temperature, injection energy, etc. It was found that the achievable Q value for the bean type was always about 30 % larger than for the D-type cases, where Q = fusion power/beam power. With strong beanness, Q ∼ 6 for DEMO type tokamaks (∼500 MWth) and Q ∼ 20 for power reactor size (4.5 GWth) are achievable. On the other hand, the Q value would not exceed sixteen for the D-type machines. (author)

[en] The compact reversed shear tokamak CREST is a cost competitive reactor concept based on a reversed shear high β plasma and water cooled ferritic steel components. The moderate aspect ratio A = 3.4 and the elongation κ = 2.0 of CREST are very similar to the case of the ITER advanced mode plasma. Presentation of such a concept based on the ITER project should be worth while for formulating a fusion development strategy. The achievement of a competitive cost of electricity (COE) is the first priority for electric power industries. High β and high thermal efficiency are the most effective parameters for achieving a competitive COE. In order to achieve a high efficiency power plant, a superheated steam cycle has been adopted which permits a high thermal efficiency (η = 41%). Current profile control and high speed plasma rotation by neutral beam current drive stabilize the ideal MHD activity up to the Troyon coefficient β_N = 5.5. A cost assessment has shown that CREST could generate about 1.16 GW(e) electric power at a competitive cost. (author)

[en] The background field approach to non-abelian gauge field theory in stochastic quantization is presented. We discuss on the basis of the Zwanziger-type stochastic gauge fixing, in which we need not introduce the Faddeev-Popov ghost field. We can choose the Zwanziger function, and thus the Langevin equation, to be manifestly covariant under the background gauge transformation. Due to the background gauge covariance, we can easily find a simple Ward identity by which the β-function calculation in stochastic quantization can be greatly simplified. We give the one-loop result of the β-function which is equivalent to the normal one. We also give another β-function, β_γ, which will give the relation between the energy scale and the fictitious time scale. (orig.)

[en] A current drive scheme based on combining neutral beam-injection and ICRF wave heating is discussed. The neutral beam injection mainly supplies toroidal momentum and is sustained by ICRF wave heating. The current is generated with sufficient efficiency and can sustain the tokamak plasma in a steady state. The application of this mechanism to alpha-particle driven current is considered. (author)

[en] Beam-driven currents can be enhanced by ICRF-heating of the beam-ions carrying the currents, because the slowing down time of these fast ions for the thermalization is effectively extended by the ICRF-acceleration. The ICRF-enhanced portion of the driven currents have usually a spatial distribution different to that of the pure beam-driven current. The driven currents are estimated with 1-D model taking into account neo-classical corrections on the contribution of electron-currents. The calculation of the current-distributions, presented here, has shown that changing the ratio between the NBI and ICRF wave powers allows us to control the current-profiles in Tokamaks. (author)

[en] Silver-coated ion exchange membrane electrodes (solid polymer electrolyte, SPE) were prepared by electroless deposition of silver onto ion exchange membranes. The SPE electrodes were used for carbon dioxide (CO₂) reduction with 0.2 M K₂SO₄ as the electrolyte with a platinum plate (Pt) for the counterelectrode. In an SPE electrode system prepared from a cation exchange membrane (CEM), the surface of the SPE was partly ruptured during CO₂ reduction, and the reaction was rapidly suppressed. SPE electrodes made of an anion exchange membrane (SPE/AEM) sustained reduction of CO₂ to CO for more than 2 h, whereas, the electrode potential shifted negatively during the electrolysis. The reaction is controlled by the diffusion of CO₂ through the metal layer of the SPE electrode at high current density. Ultrasonic radiation, applied to the preparation of SPE/AEM, was effective to improve the electrode properties, enhancing the electrolysis current of CO₂ reduction. Observation by a scanning electron microscope (SEM) showed that the electrode metal layer became more porous by the ultrasonic radiation treatment. The partial current density of CO₂ reduction by SPE/AEM amounted to 60 mA cm^-2, i.e. three times the upper limit of the conventional electrolysis by a plate electrode. Application of SPE device may contribute to an advancement of CO₂ fixation at ambient temperature and pressure

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