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AbstractPerformance of the superconducting helical coils of the Large Helical Device (LHD) during the past 12 cooling cycles is reviewed. The pair of helical coils are pool cooled by liquid helium and wound with aluminum-stabilized NbTi/Cu composite-type superconductors. Intensive efforts have been made to reliably carry out excitations, as more than 20 temporary normal transitions were observed. It was found that the minimum propagation current was about 10% lower than the nominal operation current. To improve the cryogenic stability, subcooled liquid helium has been supplied since 2006 using cold compressors, and the inlet temperature is lowered to be 3.2 K. The toroidal magnetic field has been raised by 5% and the plasma parameters are being enhanced. Pulse-height analysis is successfully applied on the balance voltage and acoustic emission signals to investigate the mechanical properties of the windings and their changes in years of operation. Short-duration normal transitions are automatically detected using a sophisticated monitoring system and careful operations are continued.

AbstractThe Large Helical Device (LHD) is one of the world’s largest superconducting systems. It consists of a pair of pool-cooled helical coils, three pairs of forced-flow-cooled poloidal coils, nine superconducting bus lines, a helium liquefier and refrigerator of 10-kW class, and six dc power supplies. Its stored magnetic energy reaches 0.8 GJ. Availability higher than 99% has been achieved in the long-term continuous operation since the first cooldown in February 1998 owing to the robustness of the systems and to efforts of maintenance and operation. One major problem is shortage of cryogenic stability of the helical coil conductor due to the slow current diffusion into a thick pure aluminum stabilizer. To improve its cryogenic stability by lowering the temperature, a subcooling system was installed before the tenth cooldown. The outlet temperature of the coil was successfully lowered to 3.8 K from 4.4 K of the saturated temperature, and its operation current was increased to 11.6 kA from 11.0 kA. These experiences of modification, maintenance, and operation should be useful for next large superconducting systems.

AbstractRecent progress in the Large Helical Device (LHD) experiment during the last 2 yr is reviewed. The LHD has been extending its operational regime toward fusion-relevant conditions while taking advantage of the net-current-free heliotron concept employing a superconducting coil system. Heating capability has exceeded 10 MW, and the central ion and electron temperatures have reached 7 and 10 keV, respectively. The maximum values of beta and pulse length have been extended to 3.2% and 150 s, respectively. Several encouraging physics observations have been obtained, i.e., simultaneous achievement of the mitigation of the magnetohydrodynamic instability criteria and good confinement, and formation of an internal transport barrier. The initial results have been obtained using a local island divertor, which shows the possibility of particle control at the plasma edge.

Abstract:  A high-aspect-ratio WC-Co (tungsten carbide super hard alloy) microstructure has been produced by a new microfabrication process which combines LIGA and micro-EDM (electro-discharge machining). The 1 mm long microstructure with gear pattern has a variation of 4 μm in the outside diameter along its length. In the process, LIGA fabricated electrodes of negative geometry are electroplated in a metal plate for use in the micro-EDM. Since the arrangement is extremely precise the serial micro-EDM processes for one workpiece can be implemented by exchanging worn electrodes for new ones via X–Y positioning between the workpiece and each electrode. In this type of machining any bulk conductor can be chosen as the material, which is to be shaped into a microstructure. WC-Co chosen in this experiment has a much larger Young's modulus and hardness than ordinary electroplated materials. The fabricated high-aspect-ratio WC-Co microstructures can have high resistance to buckling and wear when used as mechanical components or tools.

Human platelet myosin forms 10S and 6S conformations, and its Ca(2+)- and Mg(2+)-ATPase activities are parallel with the transition between 10S and 6S conformation, as judged by the gel filtration, intrinsic fluorescence, and viscosity methods. The 20,000-dalton myosin light chain (LC20) is phosphorylated by both myosin light chain kinase (MLC kinase) and Ca2+, phospholipid-dependent protein kinase (protein kinase C [PKC]). The phosphorylation (1 mol of phosphate/mol of LC20) by MLC kinase shifts the equilibrium toward the 6S conformation, but that by PKC does not. The prephosphorylation of myosin by PKC prevents the effect of phosphorylation by MLC kinase on actin-activated Mg(2+)- ATPase activity, but not the effect on conformational change. Inhibition of actin-activated ATPase activity by PKC is due to a decreased affinity of myosin for actin, and no change in Vmax is observed. These results suggest that sequential phosphorylation of myosin by both kinases plays an important role in the ATPase activities of human platelet myosin.

Abstract: The largest superconducting fusion machine, Large Helical Device (LHD), is now under construction in Japan and will begin operation in 1997. Design and construction of related R&D programs are now being carried out. The major radius of this machine is 3.9 m and the magnetic field on the plasma center is 3 T. The NbTi superconducting conductors are used in both helical coils and poloidal coils to produce this field. This will be upgraded in the second phase a using superfluid coil cooling technique. A negative ion source is being successfully developed for the NBI heating of LHD. This paper describes the present status and progress in its experimental planning and theoretical analysis on LHD, and the design and construction of LHD torus, heating, and diagnostics equipments.

The protective effect of coenzyme Q10(CoQ10) on continuous electric field stimulation-induced muscular injury was investigated in cultured cells established from neonatal rat femoral muscles. After cultivation for 9 days, skeletal muscle cells contracted and relaxed rhythmically for 4 hr in response to continuous electric field stimulation (power, 5 V; duration, 5 msec; amplitude, 3 Hz). After the onset of the stimulation, lactate and lactate dehydrogenase (LDH) release and intracellular Ca2+contents ([Ca2+]i) at relaxation increased gradually. In contrast, the intracellular ATP contents decreased. The addition of 5 μM CoQ10, but not alpha-tocopherol and radical scavengers, to the culture medium protected the cells against these biochemical changes after the stimulation. Verapamil, an inhibitor of Ca2+channels, also attenuated the increase in [Ca2+]iat relaxation and LDH. These results suggested that one of the causal mechanisms of muscular injury is an increase in [Ca2+]idue to the excess entry of extracellular Ca2+and that CoQ10can protect skeletal muscle cells against such undesirable biochemical changes.

Venom from the honey bee Apis melliferainduces cardiovascular dysfunction. We studied which constituent(s) of the venom induces cardiotoxicity and how, using cultured cardiac myocytes from mouse fetuses. Among the venom constituents, only melittin caused contractile and morphological effects; other peptides, such as apamin and mastparan; enzymes, such as phospholipase A2; and low-molecular-weight compounds, such as histamine and dopamine, did not. Treatment with 4.5 μg/ml melittin, which accounts for about half the dry weight of the venom, induced the same cardiotoxic effects as treatment with 9.0 μg/ml whole venom; these effects were a transient increase in the spontaneous beating rate, then a decrease, then cessation of beating, and finally, morphological degeneration. The cardiotoxicity of whole bee venom was completely destroyed by pretreatment of the venom with antimelittin antibody. These results suggest that bee venom cardiotoxicity is attributable to melittin. When spontaneous beating ceased following the addition of melittin or whole venom, an increase in systolic [Ca2+]iwas observed. On further incubation with melittin or bee venom, morphological injury, such as balloon degeneration, occurred concomitant with a further increase in the [Ca2+]i. An extracellular Ca2+concentration of more than 10(−6) M was necessary for morphological injury. Melittin depolarized the maximum diastolic potentials, inhibited the generation of action potentials, and induced an increase in [Na+]i. Cells were protected against the melittin-induced increase in [Ca2+]iby pretreatment with bepridil, an inhibitor of Na+-Ca2+exchange, but not by Ca2+channel blockers such as verapamil. These observations suggest that the melittin-induced increase in [Ca2+]iwas due to entry of extracellular Ca2+via the sarcolemmal Na+-Ca2+exchange system.

Cylindrically shaped shieldings were made with NbTi multifilamentary composite wires wound on a bakelite bobbin and impregnated with Wood's metal. It was confirmed that Wood's metal and an upper critical field of about 1 T allow a superconducting junction between the wires. Static fields up to 1 T were applied to the shieldings and the field penetration was examined. A field of 0.5 T could be reduced to less than 10/sup -3/ T for about 30 min. The magnetic stability against a pulsed field was also examined and high performance confirmed.<>

Heat transfer characteristics in vertical liquid-helium cooling channels have been examined to understand the effect of restriction of liquid and vapor flows. Simulated channels were made to examine the steady-state and transient heat-transfer characteristics. The channel had a foil heater of stainless steel, and a movable block for hindering coolant flow was located just above or below the channel. The results indicated that the critical heat flux was considerable influenced by the hydrodynamic situations if the channel was sealed at the top or bottom. The cooling capacity of the top-sealed channels was significantly reduced. In the case of buttom-sealed channels, the critical heat flux was reduced due to vapor locking when the channel was small. These phenomena are explained in terms of the flow restriction of the updrafting vapor. The transient heat transfer was almost independent of the flow restriction.<>

The impregnation of magnet windings with epoxy resin is widely used in developing high-performance superconducting magnets. The purpose of the epoxy impregnation is to prevent wire motion, to enhance the rigidity of the windings, and to assemble the windings in one body. Composite beams simulating an impregnated coil have been examined in order to investigate the effect of mechanical disturbances such as bond failures or epoxy cracks on the stabilities. Since the elastic energy stored in impregnated coil could be released as heat, the sudden change of rigidity during deformation would induce the mechanical disturbances which could quench the superconducting windings. Mechanical disturbances simultaneously release acoustic emissions, hence, the disturbances were monitored by thermocouples together with an acoustic-emission measuring apparatus. The change of macroscopic mechanical properties was measured in terms to the load-displacement curve of the windings. The stress analysis was made using the finite-element method (FEM). It was confirmed experimentally that the epoxy crackings and bond failures could induce the rigidity degradation and cause the heat generation which could result in a premature quench. Such disturbances were successfully estimated by the FEM analysis.<>

Results are reported from studies examining the applicability of a superconducting high-gradient magnetic separator to the extraction of uranium from seawater. Factors affecting the efficiency of separation such as shape of the filter cross section, diameter, diameter of separated particles, susceptibility, and external field were examined. In the tests two types of stainless-steel filaments of 30- and 100- mu m diameter were prepared and inserted into a matrix of CuO and Fe/sub 2/O/sub 3/ particles. It was found possible to separate the particles selectively according to susceptibility.<>

Radioiodinated erythropoietin (Epo) was bound specifically to the cells of two non-erythroid clonal lines, PC12 and SN6, which expressed neuronal characteristics. The binding was time-, cell number-, and dose-dependent and was reversible. Although the cloned Epo receptor from PC12 cells (derived from rat adrenal medulla) was identical to that from rat erythroid cells, significant differences in the ligand binding properties between two cell lineages were found; 1) PC12 cells had a single class of binding sites with very low affinity (Kd = 16 nM), whereas erythroid cells had two classes of binding sites with different affinities (Kd = 95 pM for high affinity sites and 1.9 nM for low affinity sites), and 2) cross-linking experiments revealed one cross-linked product of 105 kDa for PC12 cells and two products of 140 and 120 kDa for erythroid cells. Taken together with additional results, the presence of a putative accessory protein(s) that may alter the ligand binding affinity through interaction with Epo receptor is discussed. The binding of Epo to PC12 cells caused a rapid increase in the cytosolic concentration of free calcium. The presence of EGTA had no effect on the Epo binding but completely inhibited the calcium increase, indicating that Epo stimulated the calcium influx from outside of the cells. The addition of Epo to the culture media of PC12 cells elevated the intracellular concentrations of monoamines.

A high-speed monolithic receiver, consisting of a waveguide pin photodiode and an HEMT distributed amplifier, was packaged in a fibre-pigtailed module. It achieved a sensitivity of –22.7 dBm at 40 Gbit/s and a clear eye-opening at 50 Gbit/s. Such a performance is a first for a monolithic photoreceiver module.

The Balmer line intensities of atomic hydrogen from the WT-III tokamak plasma have been observed and interpreted in terms of the collisional-radiative model. The atomic and molecular hydrogen densities are deduced together with the electron density. Going from the plasma centre to the edge region along the minor radius, the atomic hydrogen density increases slightly and molecular hydrogen is found only in the periphery. In the edge region, the atomic hydrogen density reaches 1 × 1016m?3and the molecular hydrogen density 4 × 10l7m?3. The electron density distribution is consistent with that determined by infrared laser interferometry.

A high-efficiency uni-travelling carrier (UTC) photodiode has been developed which employs an edge-illuminated refracting-facet photodiode (RFPD) structure. The fabricated UTC-RFPD shows a maximum responsivity of 0.48 A/W even with an absorption layer as thin as 280 nm, and a high output peak-to-peak voltage of 1.5 V at 40 Gbit/s.

A long-wavelength monolithic photoreceiver has been fabricated using a multimode waveguide pin photodiode and an HEMT loss-compensated distributed amplifier. It provides an O/E conversion factor of 105 V/W and a 3 dB-down bandwidth of 52 GHz, which is the largest bandwidth for any integrated photoreceiver reported to date.

Wavelength dependence was measured for a one-directional output optical frequency conversion device that has an asymmetric-coupling-coefficient (k) distributed-Bragg-reflector (DBR) structure. The output power of converted light from the light input end is 30 dB smaller than that from the output end. The injected light wavelength and polarisation dependence of converted light power has also been investigated. The converted light wavelength scanning range is confirmed to be the design value of 4 nm, which is the widest ever reported.

A monolithic photoreceiver OEIC for λ = 1.55 µm consisting of a waveguide pin photodiode and an InAlAs/InGaAs HEMT distributed amplifier has been fabricated using a single-step MOVPE growth technique. It has a 3 dB-down frequency of 20 GHz and operates at 20 Gbit/s with a sensitivity of –10.4 dBm.

The authors report the tunable wavelength conversion of a 10 Gbit/s signal over a broad wavelength range of ~90 nm using a superstructure grating distributed Bragg reflector (DBR) laser.

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