[en] We have continued an investigation on superconducting magnetic energy storage (SMES) systems. Here, we review recent progresses in the Kyushu community, in relation with a national project of SMES by the Agency of National Resources and Energy in MITI of Japan. (orig.)

[en] At the Max-Planck-Institut fuer Plasmaphysik (IPP), Garching, the Wendelstein 7-X stellarator (W 7-X) is in the stage of the beginning R and D phase. The experiment will be a large modular machine with nonplanar coils, following the Garching development line. It fits into the range of next step devices. The main technical parameters are: Major radius: R₀=5.5 m, magnetic induction: B₀=3 T, stored magnetic energy: W_m=600 MJ, average plasma radius: r₀=0.53 m. The expected plasma parameters are: Central temperatures: T_i(0), T_e(0)=2-5 keV, central electron density: n_e(0)=0.1-2x10²⁰ m^-3, energy confinement time: τ_E=0.1-0.5 s, average beta value: <β>≤0.05. The design has to allow steady-state plasma operation. Consequently the coil system is superconducting. An internally cooled cable-in-conduit conductor with copper stabilized NbTi strands will be used at 4 K (LHe). The paper presents an overview of the design features of the machine and describes in particular the conductor design, the coil arrangement with electrical, hydraulic and mechanical parameters as well as the sequence of prototype steps which are foreseen for establishing a well-developed series production of the magnet. (orig.)

[en] The Module Coil (TOKI-MC) was designed and fabricated in order to study the mechanical properties of the helical coils of the Large Helical Device (LHD). The magnetic field inside the winding of TOKI-MC has been calculated assuming that the current density is uniform in the winding and the cross section perpendicular to the current is rectangular. The maximum magnetic field is 7.6 T and the electromagnetic force per unit length is about 11 MN/m. Stress analysis has been performed by using the finite element method in order to investigate the deformation behavior of the winding. The twisted solenoid winding tends to become a normal solenoid one and then the stress to the coil case is up to 35 MPa. The possibility of generation of a normal zone may be suggested. (orig.)

[en] A new method to detect the quench of a superconducting magnet is presented. This method detects a change of the acoustic transfer function of a magnet caused by the local temperature rise, wire movement, etc. This time, we have tried to improve the detection sensitivity to a temperature rise of 2-3 K. Some experiments have been carried out using a small epoxy impregnated superconducting magnet and a plain GFRP rod. Experimental results show that although the gain characteristics of the transfer function do not change clearly, the phase characteristics show a clear change through the local temperature rise. We have also considered the optimal frequency of the acoustic wave for the detection of the local temperature rise. (orig.)

[en] The characteristics of a possible disturbance should be taken into consideration when we design high-current density superconducting wires or magnets. The minimum quench energy (MQE) is used as measure of stability. The frictional motion of the wire is the disturbance which is most responsible for the quench. The magnitude of MQE is influenced by its time duration, but the dependence of MQE on the copper to superconductor (Cu/SC) ratio is not so influenced by its time duration of reasonable value. The spatial size of the possible disturbance is difficult to predict, but the numerical results show that, when the spatial size of the disturbance is much smaller than the MPZ, its influence on MQE and the optimum Cu/SC ratio is not significant. When we design a wire with small overall current density, a larger Cu/SC ratio is favorable to attain larger MQE. When we design a wire with high overall current density, a smaller Cu/SC ratio gives larger MQE. However, especially, in an intermediate region of overall current density, the influence of Cu/SC ratio on MQE is small. (orig.)

[en] Predictability and control over temperatures and stresses are necessary in order to assure acceptable tritium release, component reliability and lifetime in solid breeder blankets. These blankets usually contain beryllium multiplier in either pebble-bed or solid block forms. For the solid block forms, uncertainties remain in the prediction of the thermal resistance between the Be and its cladding. Several parameters are important, including surface roughness and flatness, background gas pressure, and external loads which may result from blanket thermal deformations and/or pressure stresses. Differential thermal deformation between Be and steel can cause separation to occur between the two solid surfaces, which could seriously degrade the heat transfer. Existing models and data for solid-solid conductance show inconsistencies, even for steel surfaces. Little data or none exists for the Be-steel system, in which differential surface deformations are expected. In this work, we describe a new model which incorporates the combined influences of thermal deformation and contact pressure. Data were taken with small Be specimens as a function of the relevant parameters. The results show that the inclusion of non-conforming surfaces provides a richer range of behavior. Thermal deformations degrade the heat transfer by about a factor of two from flat surfaces, but this effect tends to decrease above about 100 kW m^-2. Contact pressure (above about 1 MPa) between the two materials can effectively maintain good conductance. The flatness and roughness of the surfaces are the most critical parameters. The work also demonstrates the large degree of variation in conductance with background gas pressure. (orig.)

[en] Preliminary key issues for a synchrotron radiation-enhanced compact fusion advanced Brayton (CFAB) cycle fusion reactor similar to the CFAR (compact fusion advanced Rankine) cycle reactor are presented. These include plasma operation windows as a function of the first wall reflectivity and related issues, to estimate an allowance for deterioration of the first wall reflectivity due to dpa effects. It was found theoretically that first wall reflectivities down to 0.8 are still adequate for operation at an energy confinement scaling of 3 times Kaye-Goldston. Measurements of the graphite first wall reflectivities at Nagoya University indicate excellent reflectivities in excess of 90% for CC-312, PCC-2S, and PD-330S in the submillimeter regime, even at high temperatures in excess of 1000K. Some engineering issues inherent to the CFAB cycle are also discussed briefly in comparison with the CFAR cycle which uses hazardous limited-resource materials but is capable of using mercury as coolant for high heat removal. The CFAB cycle using helium coolant is found to achieve higher net plant conversion efficiencies in excess 60% using a non-equilibrium magnetohydrodynamic disk generator in the moderate pressure range, even at the cost of a relatively large pumping power, and at the penalty of high temperature materials, although excellent heat removal characteristics in the moderate pressure range need to be guaranteed in the future. (orig.)

[en] A concept for the application of ICRF (ion cyclotron resonance frequency) fields in a divertor is proposed to control the back-flow of recycled He ions and to reduce the He build-up in the core plasmas. The three-dimensional motions of He ions are traced by particle simulations in a divertor system. The simulation results show the applicability of the ICRF control systems. (orig.)

[en] The concept and the key features of the Joint European Torus (JET), flagship of the integrated European fusion research programme, departed considerably from those of other large tokamaks under design in the early 1970s. D-shape toroidal coils and vacuum vessel and large volume high current plasma were unique and controversial features of JET. Moreover, since the early phase of the JET design, due consideration was given to D-T operations, including remote handling capability and D-T compatible peripheral systems. JET experimental results have confirmed the validity of these design choices. In turn, these choices had an impact on the development of other tokamaks and of 'next step' design proposals, such as NET (Next European Torus) and later ITER (International Tokamak Experimental Reactor). Experimental evidence from JET and other tokamaks has clearly shown that the control of impurities is a key issue for finalizing ITER design. Therefore, the present JET programme is focussed on a divertor programme with thermonuclear grade plasmas tailored to ITER needs and to the exploration of advanced tokamak concepts for further enhanced global performance. (orig.)

[en] Heat transfer intensification in the process of liquid metal flow in a magnetic field represents a rather important problem in connection with fusion reactors. In this paper we present a review of experimental investigations carried out in this direction during the last decade at the Centre for MHD Studies of Ben-Gurion University. We have studied the influence of the transverse magnetic field on turbulence in mercury flow with various turbulizers. In certain cases a jump-wise growth in fluctuation intensity with magnetic field is observed. This leads to the enhancement of heat transfer from the wall. Recently heat diffusion processes in two-dimensional turbulent flows have been studied in experiments with thin (0.5mm) heated grids. A considerable increase in velocity fluctuation intensity is observed behind such grids in the low temperature portion of the spectrum. Here the type of temperature fluctuation spectrum depends on the magnetic field value. The temperature fluctuation intensity decreases in fields of the order of 0.5T, while a further field increase leads to its enhancement. (orig.)