A net momentum exchange during the charge exchange process produces an effective force acting on ions, which may dominate the ambipolar electric field to drive the ions into the anti- E × B vortical motion. In this circumstance, the logarithm of the neutral density profile determines the vorticity distribution of the ion flow field.

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Following the Engineering Design Activity of ITER, joint implementation towards construction has been made among the international partners. To this end, in Japan, efforts have been made to develop a fundamental approach for ensuring safety and establishing associated codes and standards for structural and seismic integrity in licensing preparation. This paper gives an outline of a safety approach and presents an outline of technical codes for the integrity of unique ITER components.

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Based on the fundamental approach for safety of ITER, a possible extension of it to assure the safety of fusion power plant was considered. Although the entire an alysis and licensing preparation are specific for ITER, its methodology which takes full advantage of the inherent features of fusion is expected to be applied to the fundamental logic of fusion power plants. Both energy and radioactive source terms that could be potential hazards are typically operative for a number of days rather than for a year, as in the case of fission. The major differences from the test reactor ITER were identified as the power blanket, coolant loop, and a generator train that will hold high temperature and a considerable amount of tritium. It is anticipated that the tritium inventory and most of the tritium plant would essentially be same as those for ITER, tritium recovery and removal from the blanket loop will dominate the fusion power plant tritium systems. Such a tritium system will actively remove tritium at a daily throughput of the order of plant inventory. This feature suggests that no dedicated off-normal systems are needed to assure the safety of the fusion plant in terms of environmental tritium release.

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There is some general concern that economic development in developing countries will hasten global warning. In terms of reducing CO₂ emissions, fusion will have great potential as a primary energy in the late 21st century according to the results of WING model simulations based on scenario analysis, if the cost of fusion with hydrogen generation would become competitive compared with those of other substitutive energies. However, securing social acceptance is very important to maintain the fossil research funded by the government suffering from cumulative debt.

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Fusionreactordesignandeconomicstudybasedonasteady-statetokamakhavebeenreviewed. Keyissues for designing an environmentally-attractive tokamak reactor are as follows; the improvement of plasma confinement, normalized beta value, density limit, and bootstrap current fraction from the aspect of plasma physics, and the maximum magnetic field of the toroidal field coil, neutron flux and thermal efficiency from the engineeringaspect. The results for the Cost of Electricity (COE) obtained by using various system an alysis codes have briefly reviewed. In comparison with other power plants, the feasibility of economically-competitive tokamak reactors is discussed.

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Waste management at fusion power plants is reviewed. Recent study indicates that most of the waste from a fusion reactor can be cleared from regulatory control over a 50-year cooling after decommissioning. In addition, the remaining metal radioactive waste is anticipated to be recyclable within 100-year cooling. These results indicate the prospect of a low emission system of fusion energy materials.

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This paper outlines the use of nuclear fusion as a global warming mitigation technology. Life cycle CO₂ emission from a nuclear fusion plant is quite low; it is comparable to that of nuclear fission. Nuclear fusion has the potential to contribute future energy systems and environment. The technological feasibility of nuclear fusion should be demonstrated in order to begin clarifying the potential contribution of nuclear fusion as well as to educate those outside of the fusion community about its potential.

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Energy model analysis estimates the significant contribution of fusion in the latter half of the century under the global environment constraints if it will be successfully developed and introduced into the market. The total possible economical impact of fusion is investigated from the aspect of energy cost savings, sales, and its effects on Gross Domestic Products. Considerable economical possibility will be found in the markets for fusion related devices, of currently developing countries, and for synthesized fuel. The value of fusion development could be evaluated from these possible economic impact in comparison with its necessary investment.

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The primacy of a nuclear fusion reactor in a competitive energy market remarkably depends on to what extent the reactor contributes to reduce the externalities of energy. The reduction effects are classified into two effects, which have quite dissimilar characteristics. One is an effect of environmental dimensions. The other is related to energy security. In this study I took up the results of EC's Extern Eproject studies as are presentative example of the former effect. Concerning the latter effect, I clarified the fundamental characteristics of externalities related to energy security and the conceptual framework for the purpose of evaluation. In the socio-economical evaluation of research into and development investments in nuclear fusions reactors, the public will require the development of integrated evaluation systems to support the cost-effect analysis of how well the reduction effects of externalities have been integrated with the effects of technological innovation, learning, spillover, etc.

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Based on the last decade of JAERI reactor design studies, an advanced commercial reactor concept (A-SSTR2) that meets both economical and environmental requirements has been proposed. The A-SSTR2 is a compact power reactor (R_p = 6.2 m, a_p = 1.5 m, I_p = 12 MA) with a high fusion power (P_f = 4 GW) and a net thermal efficiency of 51%. The machine configuration is simplified by eliminating the center solenoid (CS) coil system. An SiC/SiC composite for the blanket structure material, helium gas cooling with a pressure of 10 MPa and an outlet temperature of 900°C, and TiH₂ for the bulk shield material are introduced. For the toroidal field (TF) coil, a high temperature (T_C) superconducting wire made of bismuth with a maximum field of 23 T and a critical current density of 1,000 A/mm² at a temperature of 20 K is applied. In spite of the CS-less configuration, a computer simulation gives satisfactory plasma equilibria, plasma initiation process, and current ramp-up scenario. The current rampup time is about 22 hours. The MHD stabilities for the ballooning mode and the ideal low n kink-modes are confirmed. The stabilization of n = 1 and n = 2 kink modes requires a shell position closer than 1.4 times and 1.2 times the plasma minor radius, respectively. With regard to the divertor thermal condition, it was found that a neon gas-seeded divertor plasma with a fraction of ˜ 2.5% gives a thermal load reduction at the divertor plate from 460 MW to 100 MW and a plasma temperature drop at the divertor plate from 200 eV to 20 ˜ 30 eV. By increasing the shield thickness by about 15 cm, the total radwaste is dramatically reduced. The radwaste percentage relative to the total waste is reduced from 92 wt.% to 17 wt.%.

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Recently magnetic confinement theories in helical systems have been developed, and various magnetic configurations have been proposed. Heliotron J was constructed to optimize the helical-axis heliotron concept by introducing bumpiness in the magnetic spectra. The ECH system with 53.2 GHz and 70 GHz gyrotrons in Heliotron J produced a plasma with T_e= 1 keV and n_e=1.5×10¹⁸ m^-3, which is in the rare collisional regime. Preliminary estimation of the global energy confinement time is close to that expected from ISS95-scaling. Impurity behavior in the Heliotron J plasmas is also reported.

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Loss regions in the plasma particles' velocity space are decreased by the electrostatic potentials created on both sides of the plasma, which results in the improvement of the axial confinement in the tandem mirror. We found experimentally that the ion loss region was in contact mainly with both a plug potential bounce region and the outer mirror throat bounce region in which ions were bounced near the outer mirror throat of the plug/barrier cell. These bounce ions play an important role in tandem mirror confinement. The outer mirror throat bounce region is caused by the relatively high potential in the neighborhood of the outer mirror throat. The core plasma's radial potential profile was controlled by changing the potential of coaxially separated end plates, and it was found that control of the radial potential profile was useful for retardation of the radial loss of the bounce ions. We observed a hump structure on the energy distribution function of the end-loss ions, and found that the enhancement of the end-loss ions was caused by ion flow from the trapped region to the loss region due to Alfvn Ion Cyclotron (AIC) fluctuations. Although the ion diffusion due to the fluctuations enhances the axial ion loss, the axial loss can be reduced by creation of a higher confining potential.

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