Strand movements in cable-in-conduit conductors

The compression tests with dummy bundles have been performed to investigate the strand movements in cable-in-conduit conductors. The bundle consists of 20 mm long vinyl tubes. The cross section of the bundle is a round-cornered rectangle of 10 mm × 20 mm. Body force was applied in the transverse direction by means of a pressurized argon gas flow at room temperature. Pressure gradient in the bundle produced body force acting on each strand. The strand movements were observed with a CCD camera. Surface pressure was also applied with a piston, and a comparison has been made between two methods. Influence of a sub-bundle structure on the movements is also investigated

Magnetic Field and Force of Helical Coils for Force Free Helical Reactor (FFHR)

The electromagnetic force on a helical coil becomes smaller by decreasing the coil pitch parameter which is the angle of the coil to the toroidal direction. This makes it possible to enlarge the central toroidal field or to simplify the supporting structures of the coil. The plasma minor radius, however, becomes smaller with the pitch parameter, and a higher field is necessary to attain the same plasma performance. Another important item in a helical reactor is the distance between the helical coil and the plasma to gain enough space for blankets. In order to reduce the mass of the coil supports, a lower aspect ratio is advantageous, and an optimum value of the pitch parameter will exist around 1.2 and 1.0 for the helical systems of the pole numbers of 2 and 3, respectively

Numerical Analysis on the He II Heat Transport in Channels with a Porous Spacer

Heat transport characteristics in a pressurized He II channel have been studied, using two-dimensional numerical code that is based on the two fluid model. In general, He II heat transport performance gets worse in a either long or narrow channel [1]. If a porous medium is used as a part of the channel to transfer heat to a next channel, it will be expected to improve the heat transport in the channel. In this study, numerical model was based on the channel formed by two FRP plates in parallel and a spacer was inserted in the middle of the channel to divide into two regions. A heater was placed in one of FRP plate to input heat to the channel. Two kinds of spacers were used in the analysis to compare heat transport characteristics; (l) porous spacer, (2) FRP spacer. The temperature distribution and flow velocity vectors of He II in the channel were calculated with a steady state heat input. According to the calculated results, the temperature increase of He II in the heated channel was suppressed in the case of a porous spacer. In addition, the mass flow induced by the thermo-mechanical effect of He II enhanced heat transport capability. The paper also discusses the He II flows within the channel

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

Design and Performance of Superconducting Magnets for Hybrid Magnets(Part I. Establishment and Tests of Hybrid Magnet System at HFLSM)

Design, construction and performance of three superconducting magnets for the hybrid magnets installed in the High Field Laboratory for Superconducting Materials are described in detail. The compact solenoid, SM-3, without fully cryostable design forms the outer part of the most compact hybrid magnet in the world, HM-3 (32 mm bore, 20 T). Fully cryostable superconducting magnet designed under the Steckly criterion, SM-2, is the outer part of HM-2 (52 mm bore, 23 T), which has been most attractive to many experimentalists. SM-1, the outer part of HM-1 (32/52 mm bore, 31/28 T), with the Williams cryostability criterion is the world largest one of the superconducting magnets which employ Ti-doped Nb_3Sn multifilamentary conductors and can generate more than 12 T

Stable long-term operation of superconducting current-feeder system for the LHD

A superconducting (SC) current-feeder system is used as the current transmission lines for the experimental fusion device, LRD. It consists of nine flexible SC bus lines with total length of 497 m, and nine pairs of gas-cooled current leads. To avoid the propagation of the ice on the leads, the temperature of the terminals had been kept in the range between 5 and 20 degrees C by the heaters. The measured voltage drops of all leads were less than 20 mV. The liquid helium levels of the leads and the sub-cooler tank will equalize by the siphon method. The total time of the coil excitations exceeds 3000 hours. We have demonstrated successfully that the SC current-feeder system was stable and easy to handle, and is useful for the SC experimental fusion device

Analysis on the cryogenic stability and mechanical properties of the LHD helical coils

Transient normal-transitions have been observed in the superconducting helical coils of LHD. Propagation of a normal-zone is analyzed with a numerical simulation code that deals with the magnetic diffusion process in a pure aluminum stabilizer. During excitation tests, a number of spike signals are observed in the balance voltage of the helical coils, which seem to be caused by mechanical disturbances. The spike signals are analyzed by applying pulse height analysis and the mechanical properties of the coil windings are investigated

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

Analysis of the normal transition event of the LHD helical coils

Normal transitions and a subsequent quench were experienced with the pool-cooled helical coils of the Large Helical Device (LHD) during its excitation test. Although the initiated normal zone once started to recover, a disruptive transverse propagation followed and triggered an emergency discharging program. The cryogenic stability of the composite-type superconductor has been studied by sample experiments as well as by numerical calculations. Due to the rather long magnetic diffusion time constant in the pure Al stabilizer, transient stability of the conductor seems to play an important role for driving finite propagation of a normal zone. The cause of the final quench is also discussed from the viewpoint of cooling deterioration due to a possible accumulation of He bubble

Effectiveness of Preradiosurgical Embolization with NBCA for Arteriovenous Malformations - Retrospective Outcome Analysis in a Japanese Registry of 73 Patients (J-REAL study)

PurposeRecent reports have posed doubts about the effect of preradiosurgical embolization in brain arteriovenous malformation (AVM) because it makes the planning of stereotactic radiosurgery (SRS) difficult and has the risk of recanalization out of the target. We investigated whether the performance and quality of embolization may influence the success of SRS based on a retrospective case cohort study.Materials and MethodsSeventy-three patients who underwent embolization followed by SRS between 2003 and 2012 in eight institutes with neurointerventionists were considered. They were divided into the following two groups at 3 years of follow up after the final SRS: “successful occlusion group” (S group), with radiologically complete occlusion of AVM; and “non-successful occlusion group” (N group) with persistent remnant nidus or abnormal vascular networks. Patient background, AVM profile, embolization performance grade and complications were compared in each group. The quality of embolization was evaluated with the new grading system: embolization performance grade (E grade), specializing the achievement of nidus embolization. E grade A was defined as sufficient nidus embolization with more than half of the total number of feeders achieving nidus penetration. E grade B was defined as less than half achievement of nidus embolization, and E grade C was defines as failure to perform nidus embolization.ResultsForty-three patients were included in the S group, and 29 patients were included in the N group. The size and Spetzler-Martin grade of AVM and the rate of diffuse type was higher in the N group without statistical significance. The embolization performance level according to E grade indicated a significantly higher rate of successful embolization with more than 50% of nidus penetration in the S group (P<0.001). This difference was also confirmed in the subanalysis for limited cases, excluding smaller AVMs with complete occlusion with SRS alone (P=0.001).ConclusionThe cause of the unsuccessful result of post-embolization SRS might be the large, diffuse angioarchitecture, but proper embolization with a high rate of nidus penetration to avoid recanalization is more important. Effective embolization is essential to contribute to and promote the effect of radiosurgery