[en] The theory of the free-electron laser dynamics operating in a storage ring is reconsidered within the framework of an analytical treatment. It is pointed out that the dynamical behaviour can be characterized by the round trip evolution of self-reproducing optical field configurations (the supermodes) which allow the understanding of the laser spectral and spatial features. Simple expressions for the threshold gain and for the system efficiency are also derived

[en] Fe-sheathed MgB₂ wires doped with C and TiC nanoparticles in the formula MgB_2-xC_x+yTiC(x = 0, 0.05, 0.1, 0.15, 0.2, and y = 0, 2.5 wt.%, 5 wt.%) were investigated. X-ray diffraction patterns indicate that the core materials in the wires contain small amount of Fe₂B and MgO impurity phases, and the peaks shift with the variation of doping amount. It is found that the critical temperature T_c decreases with the increase of doping amount. Strong in-field current carrying capability enhancement was observed on MgB_1.95C_0.05+2.5 wt.% TiC.

[en] Impact hammers are important components of impact crushers, and are often shortlived due to the high-impact nature of their use. Wear-resistant alloys are welded to the surface of impact hammers to prolong their service life. In this paper, a simulation model of the rotor and impact hammers in impact crushers was designed to utilize the Discrete Element Method (DEM). The wear-resistant alloy on each impact hammer was divided into twenty-two action regions. The load distribution on each alloy block is affected by the structural and manufacturing parameters of the impact crusher. The wear distribution of the impact hammer was measured by shape morphology according to relative impact crushers. The results demonstrated that the real measurements of wear distribution on the impact hammer were similar to simulated load distribution measurements on the same surface. The study of load distribution of impact hammers by DEM established a theoretical foundation on which to base the optimal design of impact crushers. (paper)

[en] Ni based alloys have received considerable attention as the substrates for HTS coated conductors due to improved mechanical properties and reduced magnetization. Powder metallurgy is one of the promising processes for the fabrication of long alloy textured substrates. In this paper, Ni-3 at.% W alloy substrates were prepared by using high purity metal powders as starting materials. The Ni and 3 at.% W powder mixture was high energy ball milled for different periods, isostatically pressed, sintered, rolled and texture annealed. The high energy ball milling process made the powders mix uniformly and the grain sizes decrease significantly, which led to higher boundary energy and residual strain energy. The longer ball milling period resulted in a finer grain size and sharper texture in the substrate, which were confirmed by EBSD and SEM analysis. SEM and AFM observations indicate the surface of textured Ni-3 at.% W substrates is smooth and the roughness value (R_rms) is about 1.126 nm, which is suitable for deposition of buffer layers

[en] To produce ionospheric plasma environments at ground level is essential to get information not only for the development of CubeSat-class spacecraft but also for the design of ionospheric plasma instruments and to confirm their performance. In this paper, we describe the principle of plasma generation and characteristics of the back-diffusion plasma source, which can produce in-lab plasma similar to the Earth’s ionosphere, E and F regions, conditions of electron and ion temperature and density. The ion and electron energy distributions of the plasma generated by a back-diffusion source are measured by means of a cleaned Langmuir probe and gridded particle energy analyzers. The ion motion in front of the source is investigated by a hard-sphere collision model in SIMION software and the simulation results are comparable with the findings of our experiment. Furthermore, plasma densities and ion temperatures at different positions in front of the source are also demonstrated. The back-diffusion source has been accommodated for ionospheric plasma productions in several Asian institutes. The plasma characteristics of the source shown in this paper will benefit space research groups in the development of space plasma instruments. (paper)

[en] Ni and Ni-based alloys have received considerable attention as the substrates for HTS coated conductors. A critical step in the successful fabrication of coated conductor composites on metal substrates is to produce cube texture by mechanical deformation using the rolling assisted biaxial textured substrate (RABiTS) approach. In this paper, we investigated the effects of mechanical deformation and heat treatment on the growth of texture in nickel and nickel-tungsten alloys with the objective of understanding mechanisms of mechanical texturing in coated conductor substrates. The results show that the sharpest cube texture is obtained by cold rolling nickel and nickel tungsten alloys in passes of less than 5% deformation followed by annealing at high temperature

[en] Two 1.3m-long X-band accelerating structures were made to study the fabrication of the structure for the main linac of linear collider. One of the structures is being high-power tested to confirm the basic high field performance of such a full-scale structure. Various experimental instrumentations were carefully prepared; recording the RF pulses as the break down occurs, recording the timing, position and strength of X-rays along the structure, measuring dark current towards upstream and downstream along the beam axis, etc. Using these monitoring devices, the process of conditioning for the structure until reaching the specified field level or beyond is being studied. In the present paper are described those instruments and a preliminary conditioning result up to a power level of 1 MW. (author)

[en] Melt-textured YBCO superconductors are capable of carrying higher current densities than comparable copper conductors, and can therefore be used in electromechanical devices requiring high power densities. The advantage of textured YBCO superconductors is most pronounced in large systems such as electromagnetic launchers for aircraft carriers. In general, an electromagnetic launcher consists of a series of stationary pulsed electromagnets (the primary), which attract and/or repel a carriage carrying one or more magnets (the secondary). Several possibilities exist for the incorporation of HTSs into EM launchers, with the most direct being upgrading the magnets in the secondary to melt-textured YBCO. A system was developed to study propulsive force in a coaxial-type launcher. Results from this study are presented and their implications for launcher development discussed. A second type of launcher was also studied, with a power supply integrated into the launcher primary, so that the primary serves as a superconducting magnetic energy storage system. A method of optimizing energy conversion in a system of this type has been found. The time dependence of the magnetic field in this type of launcher is presented

[en] SrTiO₃ buffer layers have been deposited on rolled Ni substrates using metal organic deposition (MOD) for HTS-coated conductors. The MOD process is based on the formation of the SrTiO₃ layer coated on the surface of a Ni substrate using dip-coating as well as spin-coating techniques from a solution-based precursor, which is prepared by dissolving strontium acetate and titanium (IV) butoxide in acetic acid and methanol. The films were annealed at 950 deg. C for 2 h under 5% H₂-Ar gas flow. X-ray diffraction (XRD) shows that the buffer layers on the Ni tape are highly oriented. The pole figure indicates a single cube-on-cube texture in addition to SEM and AFM observations revealing a continuous, dense, smooth and crack-free microstructure for the coated buffer. These results offer the potential of further manufacturing coated conductors with high current density

[en] There are several motivations for increasing the diameter of melt textured single domain discs. The maximum magnetic field produced by a trapped field magnet is proportional to the radius of the sample. Furthermore, the availability of trapped field magnets with large diameter could enable their use in applications that have traditionally been considered to require wound electromagnets, such as beam bending magnets for particle accelerators and electric propulsion. We have investigated the possibility of using large area epitaxial growth instead of the conventional point nucleation growth mechanism. This process involves the use of large Y123 seeds for the purpose of increasing the maximum achievable Y123 single domain size. The hot seeding technique using large Y-123 seeds was employed to seed Y-123 samples. Trapped field measurements indicate that single domain samples were indeed grown by this technique. Microstructural evaluation indicates that growth can be characterized by a rapid nucleation followed by the usual peritectic grain growth which occurs when large seeds are used. Critical temperature measurements show that no local T_c suppression occurs in the vicinity of the seed. This work supports the suggestion of using an iterative method for increasing the size of Y-123 single domains that can be grown