[en] In order to asses the fusion research and development, we discussed on proposals which might have possibility to overcome the critical issues of a demonstration fusion reactor. Advanced Tokamak reactor concept and a fast ignition method of laser fusion are proposed to reduce the high capital cost which is common for both of magnetic fusion and inertial fusion. Hopeful divertor concepts are also proposed for both of Tokamak and Helical reactor. These summarized presentations are appended. (author)

[en] Fusion energy system is assessed from the viewpoints of energy resources, energy ratio, environment, and economics. It is compared with other alternative major energy sources, such as fission and solar energy systems. (author)

[en] High energy density plasma is shortly introduced, i.e. what is high energy density plasma?, how to produce it?, what kinds of its application can we expect?, and also recent experimental results are briefly discussed. (author)

[en] An alternative conception of the divertor, called ''Wall Lapping Plasma'' is proposed for impurity control and ash exhaust which are one of the most serious problems in reactor-grade tokamaks. Resonant helical islands formed in the boundary region rotate when we add rotating helical field by two sets of external helical coils whose current changes alternately. Consequently the plasma surface in contact with the wall by the islands rotates along the whole wall surface, so that the plasma contamination by evaporation of wall surfaces due to local heat deposition can be avoided. Plasma particles flow along the magnetic force lines intersecting the wall by islands. Intersecting angle is very small, so that mechanical valves with small height of opening located on the wall can exhaust ash easily, since backflow of neutralized helium is small because of the narrow opening. The necessary helical field is only 1/500 of the toroidal magnetic field, the total valve area is less than several percent of the wall surface area: besides the valves are easily repairable. ''Wall Lapping Plasma'' will be interesting as an alternative of the divertor because of the simple technology. (author)

[en] Computational and experimental studies on particle and energy balances in tokamak plasmas are described. Firstly, concerning the modeling of tokamak plasmas, the particle balance considering diffusion and recycling, and the energy balance considering transport and energy losses due to impurities are discussed. Production mechanisms of gaseous and metallic impurities, which play important role in tokamak plasmas, are also discussed from a viewpoint of plasma-wall interactions. Scaling laws of density, temperature and energy confinement time are shown on the basis of recent data. Secondarily, tokamak plasmas are simulated with the above model, and anomalous diffusion and electron thermal conduction are indicated. Characteristics of a future tokamak plasma are also simulated. Stationary impurity density distributions and related energy losses, such as bremsstrahlung, ionization and excitation, are calculated taking into account diffusion and ionization processes. Edge cooling by oxygen impurities is described quantitatively compared with experiments. Permissible impurity levels of carbon, oxygen and iron in future large tokamaks are estimated. Thirdly, experimental studies on surface cleaning methods of the first wall are described; discharge cleaning in JFT-2, baking effect on the outgassing rates of wall materials, surface treatment of high-temperature molybdenum by oxygen and hydrogen gases, and in-situ coating of molybdenum by a coaxial magnetron sputter method. Lastly, problems in future large tokamaks aiming at break-even or self-ignited plasma are discussed quantitatively, such as trapped particle instabilities, impurities and additional heating. It is predicted that new conceptions will be necessary to overcome the problems and attain the fusion goal. (auth.)

[en] A pellet concept of a DT ignitor and DD fuel for an ICF reactor without a tritium breeding blanket is analytically examined under the condition that T is bred through the DD reactions. There is the additional restriction that the tritium breeding ratio in a pellet is unity, including the in situ DT burn in the DD region. Model calculations show that sufficiently high pellet gain can be obtained in a DT-DD pellet, when fuel rhoR increases to --40 g/cm² and the fraction of energy released in the DD region becomes dominant. One-dimensional neutronics calculations carried out for a reference pellet model with rhoR --40 g/cm² show that the neutron heating in the compressed pellet model is evident and the total energy of the neutrons escaping from the pellet is reduced from --2000 MJ to 330 MJ for a microexplosion of --3000 MJ. (author)

[en] An effective method for driving ICF pellet compression is proposed where neither laser beam nor charged particle beam is necessary but rather high electric pulse power is directly input into a vacant space between a shell tamper and its enclosed pellet. Electrons emitted from the pellet surface produce a dense, hot plasma on the inner side of the tamper. Photons and particles of the plasma irradiate the pelletsurface and give rise to an effective ablation-driven compression. This direct energy input to compressor (DEIC) can be done efficiently and makes it easier to picture an ICF reactor. (author)

[en] In the recycling process of impurities in a plasma, only the sputtering of first wall materials is usually considered. In the present study, not only sputtering of metal but desorption of sorbed layers by particles and reflection of incident impurity ions at the limiter are also introduced. The behaviour of impurities in the discharges of recent Tokamaks is interpreted quantitatively and the result is applied to a future large Tokamak. The nonmetallic impurity concentrations may attain plateaus in the early stage of a discharge which are lower than the permissible levels, because the desorption yield by particles may probably be decreased by discharge cleaning. On the contrary the metallic impurity concentrations tend to increase beyond the permissible levels, since the self-sputtering yield of impurity ions will become larger than unity with the increase of plasma temperatures. In this respect the method to reduce the metallic impurities is important. (auth.)

[en] Technological troubles and new approaches in a pulse-power machine: LIMAY-I as a relativistic electron and light ion beam generator are reported. Liquid Fron-113 is successfully tested as insulator of the Marx generator for the first case. We develop a new type of a SF₆ spark gap switch for the Marx generator. (author)

No abstract available