Strain Effect in MgB2/Stainless Steel Superconducting Tape

The influence of mechanical strain on the critical current (Ic) is investigated for MgB2/stainless steel (SUS316) superconducting tapes. The tapes are fabricated by using 'powder in tube' method and deformation process without any heat treatment. The tensile axial strain along tape length is successfully induced to the sample by using a U-shape holder made of stainless steel (SUS304). Two samples are examined at 4.2 K in 5 T (B is applied perpendicular to the tape surface). While the initial Ic at zero external strain state (Ic0) varies (30.4 and 33.3 A), normalized Ic (Ic/Ic0) vs. external strain relations fall on the same curve. Linear increase of Ic is observed from zero external strain state to 0.5% strain (107% of Ic0). Rapid and large degradation occurs at the strain exceeding 0.4-0.5%. High durability against stress can be expected for MgB2/stainless steel superconducting tapes.Comment: 3 pages including 2 figures, submitted to Physica

Effect of aromatic hydrocarbon addition on in situ powder-in-tube processed MgB2 tapes

We fabricated in situ powder-in-tube processed MgB2/Fe tapes using aromatic hydrocarbon of benzene, naphthalene, and thiophene as additives, and investigated the superconducting properties. We found that these aromatic hydrocarbons were very effective for increasing the Jc values. The Jc values of 20mol% benzene-added tapes reached 130A/mm2 at 4.2K and 10T. This value was almost comparable to that of 10mol% SiC-added tapes and about four times higher than that of tapes with no additions. Microstructure analyses suggest that this Jc enhancement is due to both the substitution of carbon for boron in MgB2 and the smaller MgB2 grain size.Comment: 6 pages, 4 figure

Pulsed UCN production using a Doppler shifter at J-PARC

We have constructed a Doppler-shifter-type pulsed ultra-cold neutron (UCN) source at the Materials and Life Science Experiment Facility (MLF) of the Japan Proton Accelerator Research Complex (J-PARC). Very-cold neutrons (VCNs) with 136-$\mathrm{m/s}$ velocity in a neutron beam supplied by a pulsed neutron source are decelerated by reflection on a m=10 wide-band multilayer mirror, yielding pulsed UCN. The mirror is fixed to the tip of a 2,000-rpm rotating arm moving with 68-$\mathrm{m/s}$ velocity in the same direction as the VCN. The repetition frequency of the pulsed UCN is $8.33~\mathrm{Hz}$ and the time width of the pulse at production is $4.4~\mathrm{ms}$. In order to increase the UCN flux, a supermirror guide, wide-band monochromatic mirrors, focus guides, and a UCN extraction guide have been newly installed or improved. The $1~\mathrm{MW}$-equivalent count rate of the output neutrons with longitudinal wavelengths longer than $58~\mathrm{nm}$ is $1.6 \times 10^{2}~\mathrm{cps}$, while that of the true UCNs is $80~\mathrm{cps}$. The spatial density at production is $1.4~\mathrm{UCN/cm^{3}}$. This new UCN source enables us to research and develop apparatuses necessary for the investigation of the neutron electric dipole moment (nEDM).Comment: 32 pages, 15 fugures. A grammatical error was fixe

Towards a high-resolution TOF-MIEZE spectrometer with very cold neutrons

We report the first experimental test of TOF-MIEZE technique using very cold neutrons (VCNs) towards high-resolution quasi-elastic neutron scattering spectroscopy. TOF-MIEZE is a type of neutron resonance spin echo spectroscopy with a combination of the time-of-flight (TOF) method and modulation of intensity by zero effort (MIEZE). A compact MIEZE instrument was constructed at the VCN beam port at the High Flux Reactor at the Institut Laue Langevin. By accumulating individual oscillations of raw data, we observed a TOF-MIEZE signal with an effective frequency of 50 kHz in a wavelength band of 4–6 nm. The signal contrasts were 0.59 ± 0.04 and 0.29 ± 0.03 for wavelengths of 4 nm and 6 nm, respectively. The Fourier time was estimated to be 70 ns with 6 nm VCNs in the experimental set-up

Relation of n-value to critical current in bent-damaged Bi2223 composite tape

AbstractThe relation of n-value to critical current of bent-damaged (Bi,Pb)2Sr2Ca2Cu3O10+δ (Bi2223) composite tape was studied experimentally and analytically. The experimental results showed that, under bending strain, the n-value decreased rather slightly with decreasing critical current in comparison with the data obtained under applied tensile strain. The experimentally observed slight decrease in n-value with critical current under bending strain, and the measured changes in critical current and n-value with increasing bending strain, were described satisfactorily by the presented damage evolution model that correlates the extent of damage to variation of bending strain-induced tensile strain in the core along the thickness direction

Theoretical demonstration of highly efficient cw THz generation by using composite photonic-structure elements

We theoretically propose one-dimensional composite photonic structures for high-resolution THz spectroanalysis. We compare the performance of two GaAs/AlAs composite photonic-structure devices, one with usual 1/4-wavelength layers of distributed Bragg reflectors (DBRs), and the other with the designed DBRs. The device with designed DBRs shows the optical-to-terahertz conversion efficiency up to 10^-5 and wide frequency tunability ranging from sub-THz to 3 THz. We found that the composite photonic structure allows us to control photonic modes with a high degree of freedom by flexible structure designs. This device achieve a cw THz source with a highly narrow bandwidth operating at room temperature

Experimental Signature of Medium Modifications for rho and omega Mesons in the 12 GeV p + A Reactions

The invariant mass spectra of e+e- pairs produced in 12-GeV proton-induced nuclear reactions are measured at the KEK Proton-Synchrotron. On the low-mass side of the omega meson peak, a significant enhancement over the known hadronic sources has been observed. The mass spectra, including the excess, are well reproduced by a model that takes into account the density dependence of the vector meson mass modification, as theoretically predicted.Comment: 4 pages, 3 figures, Version accepted for Physical Review Lette