Effects of spatially limited external magnetic fields on short sample tests of large-scale superconductors

For short sample tests of large-scale superconductor coil conductors, it is difficult to get sufficient spatial uniformity using external magnetic fields because of the size limitations of test facilities. The effects of spatially limited external magnetic fields on short sample tests are discussed by comparing the test results for narrow and broad external magnetic fields. The authors tested short samples of pool-cooled 10 kA class superconductors using two kinds of split coils which are different in bore size. The measured recovery currents for the narrow external field are more than twice those for the broad field. It shows that the insufficient spatial distribution of the external field biases the stability measurements of superconductor

Microcystin degradation in sphingopyxis sp. C-1

The microcystin-degrading gene cluster, mlrA-B-C-D, plaies an important role in the degradation process of hepatotoxic microcystins for several bacterial species. However after microcystin is degraded to linear-microcystin by MlrA, it is still unknown about where and by what it is metabolited. In order to clarify it, we disrupted the mlrB gene and mlrC gene in chromosome of microcystin-degrading bacteria, Sphingopyxis sp. C-1. The cells disrupted mlrB gene and mlrC gene accumulated of microcystin-degradation product, linear-microcystin and tetrapeptide, respectively, whereas the cell free extracts of ?mlrB cells detected Adda and ?mlrC cells accumulated tetrapeptide. Moreover, topology analysis of MlrB using the ß-lactamase gene fusion method insisted MlrB is the peripheral protein binding the inner-membrane. These results insist that MlrB degrades the linear microcystin in the periplasmic space and MlrC degrades tetrapeptide in cytoplasm. Thus, in intact cells, MlrC cannot degrade linear-microcystin as being separated in inner-membrane from linear-microcystin while MlrC is capable of degrading the linear-microcystin in cell-free extract

Macrophage centripetal migration drives spontaneous healing process after spinal cord injury.

Traumatic spinal cord injury (SCI) brings numerous inflammatory cells, including macrophages, from the circulating blood to lesions, but pathophysiological impact resulting from spatiotemporal dynamics of macrophages is unknown. Here, we show that macrophages centripetally migrate toward the lesion epicenter after infiltrating into the wide range of spinal cord, depending on the gradient of chemoattractant C5a. However, macrophages lacking interferon regulatory factor 8 (IRF8) cannot migrate toward the epicenter and remain widely scattered in the injured cord with profound axonal loss and little remyelination, resulting in a poor functional outcome after SCI. Time-lapse imaging and P2X/YRs blockade revealed that macrophage migration via IRF8 was caused by purinergic receptors involved in the C5a-directed migration. Conversely, pharmacological promotion of IRF8 activation facilitated macrophage centripetal movement, thereby improving the SCI recovery. Our findings reveal the importance of macrophage centripetal migration via IRF8, providing a novel therapeutic target for central nervous system injury

Lessons learned from twenty-year operation of the Large Helical Device poloidal coils made from cable-in-conduit conductors

The Large Helical Device (LHD) superconducting magnet system consists of two pairs of helical coils and three pairs of poloidal coils. The poloidal coils use cable-in-conduit (CIC) conductors, which have now been adopted in many fusion devices, with forced cooling by supercritical helium. The poloidal coils were first energized with the helical coils on March 27, 1998. Since that time, the coils have experienced 54,600 h of steady cooling, 10,600 h of excitation operation, and nineteen thermal cycles for twenty years. During this period, no superconducting-to-normal transition of the conductors has been observed. The stable operation of the poloidal coils demonstrates that a CIC conductor is suited to large-scale superconducting magnets. The AC loss has remained constant, even though a slight decrease was observed in the early phase of operation. The hydraulic characteristics have been maintained without obstruction over the entire period of steady cooling. The experience gained from twenty years of operation has also provided lessons regarding malfunctions of peripheral equipment

Stability test results on the aluminum stabilized superconductor for the helical coils of LHD

Stability tests have been carried out on short samples of the aluminum/copper stabilized composite-type superconductors developed and used for the pool-cooled helical coils of the Large Helical Device. The waveform of the longitudinal voltage initiated by resistive heaters shows a short-time rise before reaching a final value, which seems to correspond to the diffusion process of transport current into the pure aluminum stabilizer. The propagation velocity has a finite value even for the transport current being lower than the recovery current, and it differs depending on the direction with respect to the transport current

Stability and safety estimates and tests of a superconducting bus-line for large-scale superconducting coils

We have been developing a flexible superconducting bus-line as a unit electrical feeder between large-scale superconducting coils and their power supplies away from the coils. The designed superconducting bus-line consists of a pair of +/- aluminum stabilized NbTi/Cu compacted strand cables and a coaxial four-channel transfer line. A full-scale model of the SC bus-line (20 m long) has been constructed and tested successfully up to 40 kA without a quench under the short-circuit condition. Stability tests were also done by inducing a forced quench with heaters. A minimum propagation current larger than 32.5 kA was confirmed. Thus, the bus-line was cryogenically stabilized at the rated current of 30 kA. We have examined the test results and evaluated the stability and safety margins of this bus-line. The design criteria for a superconducting bus-line are also shown for large-scale superconducting coils with operating current as a parameter

Asymmetrical normal-zone propagation observed in the aluminum-stabilized superconductor for the LHD helical coils

Transient normal-transitions have been observed in the superconducting helical coils of the Large Helical Device (LHD). Stability tests have been performed for an R&D coil as an upgrading program of LHD, and we observed asymmetrical propagation of an initiated normal-zone. In some conditions, a normal-zone propagates only in one direction along the conductor and it hence forms a traveling normal-zone. The Hall electric field generated in the longitudinal direction in the aluminum stabilizer is a plausible candidate to explain the observed asymmetrical normal-zone propagation

Effect of Direction of External Magnetic Field on Minimum Propagation Current of a Composite Conductor for LHD Helical Coils

The conductor for helical coils of the Large Helical Device consists of a Rutherford-type NbTi/Cu cable, a pure aluminum stabilizer, and a copper sheath. The dimensions of the conductor and the stabilizer cross-sections are 18.0 mm × 12.5 mm and 12.4 mm × 5.2 mm, respectively. The measured cold-end recovery current in the magnetic field parallel to the shorter side (B//12.5) is clearly lower than that in the field parallel to the longer side (B//18.0) because of the difference in magnetoresistance by Hall currents. Since the minimum propagation current Imp is important to determine the upper limit of operation current, Imp has been measured for two types of one-turn coil samples, which were bent flatwise (B//18.0) and edgewise (B//12.5) with the inner radius of 0.14 m to extend the length in the uniform background field of the test facility. The measured Imp at B//12.5 is almost the same as that at B//18.0 in spite of the large difference in the steady-state resistance. Imp is considered to be determined by the heat balance before the current diffuses deeply into the stabilizer