The magnetic microstructure, i.e. the arrangement of domains and domain walls, forms the mesoscopic link between basic physical properties of magnetic material and its macroscopic properties. The development and optimization of magnetic materials, therefore, require a solid knowledge of the underlying domains. In most case, such as knowledge can only be obtained by direct imaging. A Kerr microscope has the great advantage of allowing easy handling and smooth observation without any auxiliary preparation. In this report, a Kerr microscope and magnetic domain imaging technique are reviewed.

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Studies on the loss of fusion produced alpha particles enhanced by toroidal field (TF) ripple in a low-aspect-ratio tokamak reactor (VECTOR) have been made by using an orbit-following Monte-Carlo code. In actual TF coil systems, the ripple loss of alpha particles is strongly reduced as the aspect ratio becomes low (the power loss is proportional to A^8.8 for A>˜2.5) and the reduction of the number of TF coils results in a large amount of ripple losses even in a low-aspect-ratio tokamak. Judging from the allowable peak heat load on the first wall (≈1MW/m²) due to loss particles, the number of TF coils of VECTOR can be reduced fro 12 to 10 without changing the coil size, and in addition, the number can be reduced to 8 with ferrite plates. To reduce the number of TF coils from 12 to 6, about 40% of coil size enlargement is necessary. By using ferrite plates, the coil size enlargement for N=6 can be reduced to about 15%.

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Installation of a heavy ion beam probe (HIBP) diagnostic in the Tokyo Spherical Tokamak-2 (TST-2) device is considered. Preliminary beam trajectory simulations with Na⁺ primary beam demonstrate that observations at a number of spatial locations on the poloidal cross-section of a typical TST-2 ohmically heated plasma are possible by selecting a manhole port of TST-2 as a beam receiving port. Beam attenuations are reasonable to consider core plasma measurements.

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The heat flux in the divertor target is one of the most crucial problems for a fusion reactor. This problem is more severe in a spherical tokamak (ST) reactor because it is more compact. This paper proposes a liquid lithium divertor system to solve this problem. The heat coming from the fusion plasma along the divertor leg is removed by evaporation of lithium. The lithium vapor is condensed on the wall, and the heat is transferred to the coolant that drives power generator. Narrow slit along the divertor leg and the differential evacuation chamber reduces leakage of lithium vapor to the plasma chamber.

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To evaluate a bootstrap-current-profile quickly, a simple method has been developed with a novel approximation. This results in that all of the neoclassical diffusion coefficients for the gradient become the polynominals only in variables of inverse aspect-ratio, ε, effective charge, Z_eff and collisionality, ν^*, in the whole range of variables. The resultant current profile is well reproduced from ITER benchmark with transport code including the case with internal-transport-barrier. This method is applied to a commercial reactor, VECTOR, low-aspect-ratio tokamak reactor. The fraction of bootstrap-current, I_BS/I_p, are evaluated as: ∼55%, ∼60% and ∼100% for the normal-shear, weakly-reversed-shear and strongly-reversed-shear (with current-hole) plasmas, respectively.

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The QUEST (Kyushu, pronounced as “Q-shu” University Experiment with Steady-state spherical Tokamak) project is promoted from 2005 in the frame work of bi-directional collaboration organized by NIFS (National Institute for Fusion Science) to study plasma wall interaction on high temperature all-metal wall in long duration plasma on a spherical tokamak configuration. Present status and future plan of QUEST are presented.

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Subjects in radiation shielding for the low aspect ratio tokamak commercial reactor VECTOR are discussed and their solutions are presented. The subjects and design criteria of radiation shielding in ITER are consulted to discussion in the present work, because of these in commercial reactors same as those in the ITER.

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The various plasma current start-up techniques and related topics in a spherical tokamak (ST) device are described. The Ohmic heating coil current clamp experiments in NSTX are described and discussed, and the plasma current start-up experiments in the STOR-M tokamak with iron core and the outer vertical field coil is presented as one of technique for a plasma current start-up in a ST.

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The design study of superconducting magnets adapting a new coil winding scheme of an indirect cooling method is reported. The superconducting magnet system for the spherical tokamak (ST), which is proposed to study the steady state plasma experiment with Q_equiv˜1, requires high performances with a high current density compared to the ordinal magnet design because of its tight spatial restriction. The superconducting magnet system for the fusion device has been used in the condition of high magnetic field, high electromagnetic force, and high heat load. The pool boiling liquid helium cooling outside of the conductor or the forced flow of supercritical helium cooling inside of the conductor, such as cable-in-conduit conductors, were used so far for the cooling method of the superconducting magnet for a fusion application. The pool cooling magnet has the disadvantages of low mechanical rigidities and low withstand voltages of the coil windings. The forced flow cooling magnet with cable-in-conduit conductors has the disadvantages of the restriction of the coil design because of the path of the electric current must be the same as that of the cooling channel for refrigerant. The path of the electric current and that of the cooling channel for refrigerant can be independently designed by adopting the indirect cooling method that inserts the independent cooling panel in the coil windings and cools the conductor from the outside. Therefore the optimization of the coil windings structure can be attempted. It was shown that the superconducting magnet design of the high current density became possible by the indirect cooling method compared with those of the conventional cooling scheme.

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Three-dimensional (3-D) localized magnetic reconnection was studied experimentally in TS-4 spherical torus (ST) merging device. When strong compression force I_Acc∼ 60 kA compressed two STs with small guide field B_X/B_¦¦∼ 1, toroidal modes n=1-3 of current sheet was observed to grow only during their reconnection. A new finding is that deformation of curret sheet causes the reconnection rate to increase. When weak compression force I_Acc∼ 0 kA compressed two STs with large guide field B_X/B_¦¦∼ 7, their reconnection rate was maintained small. These phenomena indicate that 3-D localized reconnection is one of fast reconnection mechanisms.

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Application of an externally applied rotating magnetic field (RMF) for control of MHD relaxation phenomena driven by a coaxial helicity injection has been proposed in the HIST spherical torus device. In this letter, the plasma responses to the RMF evaluated by magnetic fields inside the plasma in HIST are shown.

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Electron cyclotron current drive by electron Bernstein (EB) waves for the start-up and ramp-up of toroidal plasma current with no central solenoid in tokamaks is discussed. It is shown that high N// EB waves have ability to ramp-up the current against the counter voltage from self-induction, where N// is the parallel refractive index to the magnetic field, and they are especially suitable for initial current start-up phase where the bulk electron temperature is low enough to ensure high N// EB waves.

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TiO₂-thin-films have remarkable properties as a photocatalyst to resolve organic pollutants and an electron transporter with high energy transformation efficiency for dye-sensitized solar cells. For these applications, it is required that thin film has no apparent cracks or has high optical transparency. In this study, TiO₂-nanoparticles are synthesized and are deposited using the electrophoresis deposition method. TiO₂-nanoparticles can transport electrons by oriented attachment mechanism. Many of nanoparticles were connected with each other and formed nanowires clusters. The lengths of observed TiO₂-nanowires were not the same. All of nanowires were positively charged in colloidal aqueous solution and were attracted toward ITO glass as the negative electrode, and then thin film was deposited on it. The crystal structure of thin film was anatase-type. TiO₂-nanowires thin film with high optical transparency was deposited. A number of cracks, however, were observed as the deposition time increased and thin film was flaked off from substrate. TiO₂-thin films with no cracks could be deposited using mixture of TiO₂-nanowires and TiO₂-nanoparticles (P25). It was suggested that single nanowires were mainly deposited at ITO glass at the first stage of electrophoresis, nanowire-cluster at the second stage and then finally P25 were deposited.

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Resultant low frequency magnetic field generated was measured as a function of distance from them over broadband range (40-800Hz) and harmonic range (100-800Hz) on eleven kinds and more than two hundred recent household appliances in total. The relationship between magnetic filed measured and the power consumption of household appliances was also examined. As a result, it is verified that magnetic field from appliances is drastically reduced as the distance goes. And, any clear dependence of what on the power consumption of appliances is not recognized. Furthermore, from harmonic component analysis by using FFT for current flowing in appliances, it is assumed that relatively large amount of harmonic components with odd numbers is contained in the magnetic field.

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When a Fourier series is used to approximate a periodic and piecewise smooth function with a jump discontinuity, an overshoot at the discontinuity occurs and is called Gibbs phenomenon. For explaining understandably and systematically this Gibbs phenomenon from the educational point of view , the representation method is proposed using an accordion-like folding convergence of the extremum values for the partial sums of its Fourier series at the discontinuity. Using an integration by parts to obtain Fourier coefficients and rearranging its Fourier series, the expansions are devised to show explicitly the overshoots at the discontinuities for any functions with jump discontinuities.

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Stacking of voltage pulses by using small type transmission line transformers (TLT) is described. By using power MOS-FETs for switching devices, repetition frequency of output pulses can be several hundred kilohertz. Temperature rise of the ferrite bead core for TLT increases with repetition frequency and common mode voltage of TLT. Relation of the rise time, load resistance, and number of cores were investigated.

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To make clear the influence of algae growth at the surface of a polymer insulator in a practical transmission line, the characteristics of ac corona discharge from an aggregate algae particle were investigated. The aggregate algae particle was made of Protococcus viridis. Corona onset voltage from an aggregate algae particle was decreased as relative humidity increased. Under the condition of relatively higher relative humidity, luminous channel of corona discharge became more strongly and the number of corona pulses in the current waveform was increased. For an aggregate algae particle contaminated with sea salt including MgCl₂, corona onset voltage decreased drastically at relative humidity above 40%. This property would result from deliquescence of MgCl₂. Corona discharge was strongly affected by existence of MgCl₂ in an aggregate algae particle. Surface resistance of algae attached to the surface of the silicone rubber sheet decreased in fourth figures for relative humidity from 20 to 90%. Therefore, the existence of algae on the polymer insulator inevitably affects the electric property and the surface property of the polymer insulator.

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The optical polymer waveguide fabricated by plasma enhanced polymerization, namely plasma enhanced chemical vapor deposition (PCVD), will be a candidate for a waveguide of optical interconnection and optical functional device because of flexibility, low deposition temperature, thickness controllability and low cost. The absorption of the polymer will be an important issue for those applications. That of the polymer film, a-C:H prepared by PCVD, is caused by sp² clusters in sp³ network. In the present paper we discuss the absorption by measurement of spectral ellipsometry and with XPS signals of the valence band. As the results, optical loss of the film is lower than 1 dB/cm at 0.82 μm in wavelength. In order to decrease the loss lower than 0.1 dB/cm we need to decrease sp² cluster size and to decrease variation of the size. Moreover, we well need to decrease branch bond in the polymer. We also believe F radical will participate in the chemical reaction of double bonds creation and annihilation in the same manner of H radical.

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Studies on the development of deterioration/ performance evaluation method for outdoor electric insulation of polymer materials are pushed forward now in the International Council on Large Electric Systems (CIGRE). The small scale test method (Dynamic drop test; DDT) which could evaluate disappearance characteristics of hydrophobicity easily was suggested. This test is to evaluate resistance of a sample to loss of hydrophobicity due to moisture and simultaneous electric stress. As factors for deterioration of hydrophobicity on a sample in DDT, various factors such as electrical influence, physical influence by water droplets and so on were considered. In this study, we investigated two kinds of factors (electrification and salt) affecting deterioration of hydrophobicity on the surface of a silicone rubber until ignition of continuous electrical discharge in DDT.

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