122890200
Core-level and valence-band study using angle-integrated photoemission on LaFeAsO(0.9)F(0.1)
Using angle-integrated photoemission spectroscopy we have probed the novel LaFeAsO{sub 0.9}F{sub 0.1} superconductor over a wide range of photon energies and temperatures. We have provided a full characterization of the orbital character of the valence-band (VB) density of states (DOS) and of the magnitude of the d-p hybridization energy. Finally, we have identified two characteristic temperatures: 90 K where a pseudogap-like feature appears to close and 120 K where a sudden change in the DOS near E{sub F} occurs. We associate these phenomena with the spin density wave magnetic ordering and the structural transition seen in the parent compound, respectively. These results suggest the important role of electron correlation, spin physics, and structural distortion in the physics of Fe-based superconductors.
25110773
Planning of insertion devices for the 3-GeV Taiwan Photon Source
The Taiwan photon source (TPS) is a 3-GeV storage ring with 24 straight sections for installation of insertion devices (ID), radio-frequency cavities (RF) and electron- beam injection. Most insertion devices are in-vacuum undulators to produce intense X-rays with a brilliance up to 1times1021 photons s-1 mrad-2 mm-2 per 0.1% bw. A superconducting wiggler is also necessary to provide higher energy in the medium-energy range of the TPS. The APPLE II elliptically polarized undulator and a long- period undulator provide a source with circular and any linear polarization and the VUV source. Projects to investigate a superconducting undulator and a cryogenic permanent-magnet undulator are launched for energies in a range 1.5-25 keV.
120445064
Superconducting wiggler with semi-cold beam duct at Taiwan light source
Abstract A 3.2 T superconducting wiggler with a periodic length of 6 cm and 32 poles was designed and fabricated as an X-ray source. The beam duct of this magnet is a semi-cold, ultra-high vacuum chamber that consists of an aluminum and stainless steel taper. The number of poles in this magnet design is even, to minimize the integral strengths of the multipole components. Two measurement systems—involving room-temperature and cryogenic Hall probes—were set up to measure the field of the superconducting wiggler. A cryogenic plant that supplied liquid helium and nitrogen to the superconducting wiggler has already been established. The performance of magnet construction is good and the commissioning of the superconducting wiggler in the storage ring has been successful. No trim coil compensation on the magnet is required to adjust the electron beam orbit. Furthermore, the electron beams exhibit no loss and remain highly stable after the superconducting wiggler has been quenched.
36542122
Construction and Performance of Superconducting Magnets for Synchrotron Radiation
Two superconducting magnets, one wavelength shifter with a field of 6 T and one wiggler with a field of 3.2 T, were constructed and routinely operated at Taiwan Light Source to generate synchrotron X-rays. Additionally, three short multipole wigglers with the same field of 3.1 T are under construction and will be installed in the three achromatic short straight sections. A warm beam duct with an inner gap of 20 mm and a 1.5 W GM type cryo-cooler were used in the wavelength shifter to achieve cryogen-free operation. For the 3.2 T wiggler, a cold beam duct with an inner gap of 11 mm was kept at 100 K temperature and no trim coil compensation is necessary for its operation. Meanwhile, no beam loss was observed when it was quenched. The design concept, magnetic field quality, and the commissioning results of these magnets will be presented.
55667448
SUPERCONDUCTING UNDULATOR WITH VARIABLY POLARIZED LIGHT
This study investigates planar in-vacuo superconducting elliptically polarized undulators with periodic length of 5 cm (SEPU5) producing linearly and circularly polarized infrared rays or x-rays source. The vertically wound racetrack coil is chosen for the coil and pole fabrication of the SEPU5. When the up and down magnetic pole arrays with alternative directions rotated wires in the horizontal plane, an elliptical field radiates elliptically polarized light in the electron storage ring, the free electron laser (FEL), and the energy recovery linac (ERL) facilities. Meanwhile, an un-rotated wire magnet array is constructed together with the rotated wire magnet array on the same undulator is used to switch the linear polarization in horizontal and vertical, as well as the right- and left-circular polarization radiation. This investigation describes the main factors of the planar and helical undulator design for FEL and the concepts concerning the magnet array structures of the superconducting undulators.
30348524
Design of mechanical structure and cryostat for IASW superconducting wiggler at NSRRC
An in-achromatic superconducting wiggler (IASW) was successfully constructed and installed at the Taiwan Light Source (TLS) in January 2006. The cryostat with a 30 L liquid nitrogen aluminum reservoir shielding surrounds the helium vessel, which comprises the cold mass and 100 L liquid helium. The helium vessel is suspended by eight suspension links, which are thermally intercepted at 80 K and can be adjusted by applying tension, such that the center of the cold mass does not move during cooled to 4.2 K. A three-layered stainless tube was designed to prevent the transfer port from freezing and the steam- electricity separation system is designed to supply electricity and return the helium gas to prevent freezing of the power feedthrough.
118628184
Model-independent analysis for determining mass splittings of heavy baryons
We study the hyperfine mass differences of heavy hadrons in the heavy quark effect theory. The effects of one-gluon exchange interaction are considered for the heavy mesons and baryons. Based on the known experimental data, we predict the masses of some heavy baryons in a model-independent way.
11335733
Charge radii of light and heavy mesons
Abstract. We calculate the electromagnetic (EM) form factors of the pseudoscalar mesons in the light-front framework. Specifically, these form factors are directly extracted from the relevant matrix elements, instead of choosing the Breit frame. The results show that the charge radius of the meson is related to both the first and second longitudinal momentum square derivatives of the momentum distribution function. The static properties of the EM form factors and the heavy quark symmetry of the charge radii are checked analytically in the heavy quark limit. In addition, we use the Gaussian-type wavefunction to obtain the numerical results.
2656324
Radiative leptonic decays of heavy mesons in heavy quark limit
We study the radiative leptonic decays of heavy mesons within the covariant light-front model. Using this model, both the form factors FV and FA have the same form when the heavy quark limit is taken. In addition, the relation between the form factor FV and the decay constant of a heavy meson FH is obtained. The hadronic parameter β can be determined by the parameters appearing in the wave function of the heavy meson. We find that the value of β is not only quite smaller than the one in the non-relativistic case, but also insensitive to the value of the light quark mass mq. These results mean that the relativistic effects are very important in this work. We also obtain that the branching ratio of B→lνlγ is about (1.40–1.67)×10-6, in agreement with the general estimates in the literature.
118480874
Study of quark distribution amplitudes of 1S and 2S heavy quarkonium states
In this paper, the quark distribution amplitudes of 1S and 2S heavy quarkonium states are studied in terms of Gaussian-type wave functions. The transverse momenta p⊥ integrals of the formulae for the decay constant are performed analytically. Then the quark distribution amplitudes are obtained. In addition, the ξ-moments are also calculated. After fixing the relevant parameters appearing in the quark distribution amplitude, the curves of the quark distribution amplitude for 1S and 2S heavy quarkonium states are plotted. Finally, the numerical results of this approach are compared with the other theoretical predictions.
6982155
Neutrino-photon scattering and its crossed processes in a background magnetic field
Abstract We study the neutrino-photon processes such as γγ→ν ν , νγ → νγ , and ν ν →γγ in a background magnetic field smaller than the critical magnetic field B c ≡ m e 2 / e . Using Schwinger's formalism, we extract leading magnetic-field contributions to the above processes. Our result is valid throughout the kinematic regime where both neutrino and photon energies are significantly smaller than m W . We briefly discuss the astrophysical implications of our result.