The generation of strong periodic magnetic fields with short periodic lengths is very attractive for accelerator-based compact high-power future light sources. We have developed a new type of ...undulator using HTS bulk material to overcome the field strength limitation due to the maximum energy product ( BH ) max of permanent magnets and the engineering current density of superconducting wires. REBCO bulk is the most attractive material for realizing high-field undulators because of its extremely high J c at low temperatures. However, REBCO bulk requires a melt growth process with seed crystals to produce a single-domain superconducting bulk, and this process tends to introduce batch-to-batch variations in J c . As a result, it is difficult to precisely control the peak-to-peak magnetic field fluctuations of the periodic magnetic field. Therefore, we focused on MgB 2 , which does not show weakly linked electromagnetic behavior, and thus does not require a melt growth process with seed crystals. In this study, we demonstrated for the first time in the world the generation of a periodic magnetic field using MgB 2 bulk arrays and confirmed that the peak-to-peak fluctuations are smaller than those of REBCO bulk.
Hexagonal boron nitride (h-BN) epitaxial films were successfully grown on (0
0
0
1) sapphire substrate by metalorganic vapor phase epitaxy (MOVPE). BN films were grown using triethylboron and ammonia ...(NH
3) at various V/III ratios ranging from 210 to 2100. BN films grown at high V/III ratios above 1280 showed two X-ray diffraction (XRD) peaks, one from the (0
0
0
2) plane and the other from the (0
0
0
4) plane of h-BN, and exhibited a clear peak at 1366
cm
−1 of the first h-BN Raman mode as well. In contrast, XRD revealed that structures in BN films grown at low V/III ratios below 640 were turbostratic. These results indicate that the structure of the BN film grown on sapphire substrate by MOVPE strongly depends on the V/III ratio and that the BN growth under a high V/III ratio could lead to the growth of (0
0
0
1) h-BN epitaxial films on (0
0
0
1) sapphire substrates.
Electric railways have several problems due to electrical resistance of feeder lines such as a transmission loss and a voltage drop. In order to solve these problems, we have been developing ...superconducting feeder cable, which enables zero-resistance power transmission. Now we have been able to obtain government approval to conduct commercial operation using superconducting cables. It has been begun the commercial operations on passengers using superconducting cable for railway. One of the challenges of the superconducting feeder cable is its joining technique. To introduce superconducting feeder cable between substations, it is required to join superconducting feeder cable to each other at a railway site. First, we conducted an internal observation of the superconducting solder joint using X-ray CT and evaluated the state of the joint. It was found that joining under pressure is effective in reducing joint resistance. Therefore, we performed simple pressure joining using a tweezers-type soldering iron so that it could be performed at railway sites, and evaluated the current characteristics. Joining using this method yielded a low joint resistance on the order of 10 −11 Ω·m 2 , and was found to be effective for joining at railway sites. These results give standards of the joining of superconducting feeder cable.
A very important part of an HTS cable design is the optimization of its parameters to get the highest possible current-carrying capacity and stability. One of the possible ways to achieve it is the ...use of so-called longitudinal magnetic field effect. It is known that in magnetic fields that are parallel to a transport current, most of the superconductors, both low and high critical temperature ones, demonstrate the increase of the critical current. This effect was predicted for HTS theoretically and proved experimentally in our recent works. Although the longitudinal magnetic field effect can be used to increase the efficiency of both DC and AC HTS cables, their optimization methods should be different. In this paper, we present different optimization methods for DC and AC power cables with consideration of the longitudinal magnetic field effect, that can help to obtain the higher current-carrying capacity for DC cables and higher stability for AC power cables, i.e., lower AC loss. Two calculation methods of magnetic field in the cables are presented: analytical and with FEM model. Comparison of results of optimization DC and AC cables are presented and discussed. We also present the results of measurements and calculations of AC losses in DC cable.
Hexagonal boron nitride grown by MOVPE Kobayashi, Y.; Akasaka, T.; Makimoto, T.
Journal of crystal growth,
11/2008, Letnik:
310, Številka:
23
Journal Article, Conference Proceeding
Recenzirano
Hexagonal boron nitride (h-BN) has a potential for optical device applications in the deep ultraviolet spectral region. For several decades, only amorphous and turbostratic boron nitride (BN) films ...had been grown by chemical vapor deposition and metalorganic vapor phase epitaxy. By introducing flow-rate modulation epitaxy (FME), which enables us to reduce parasitic reactions and lower the optimal growth temperature, we have succeeded in growing single-phase h-BN epitaxial films on nearly lattice-matched (1
1
1) Ni substrates. The h-BN epitaxial films exhibit near-band-gap ultraviolet luminescence at a wavelength of 227
nm in cathodoluminescence at room temperature. The combination of FME and the lattice-matched substrate paves the way for the epitaxial growth of high-quality h-BN.
Since the 1970's the effect of the increase of the critical current of superconductors in the longitudinal external magnetic field has been known. The critical current density of a Nb-Ti wire at low ...longitudinal magnetic fields demonstrated several times the larger value compared with that in a transverse magnetic field. The same phenomenon has been observed for 2G HTS tapes. It is natural to try to use this phenomenon to increase the critical current in DC HTS power cables. In this paper, we present the analysis of feasibility to use the longitudinal magnetic field effect to increase critical currents in practical HTS power cables. The experimental model of the HTS DC cable has been developed, produced, and tested in liquid nitrogen. The increase of the critical current observed when the longitudinal magnetic field generated. This increase coincides with the calculations.
PDF
