54590931
MAGNETIC FIELD MEASUREMENT AND FINE-TUNING OF KICKERS
We have demonstrated an algorithm which promisingly can tune the pulse shape of current and magnetic field of kicker systems in-situ. This algorithm includes gap shimming of the ferrite magnets to adjust the pulse width of the excitation current and changing the resistance of the secondary coils to modify the pulse curvatures of each kicker. With the empirical formula derived from the systematic measurement on the magnetic field and the pulse current in laboratory, we can reduce the pulse-shape difference among the kicker magnets in the injection section of the storage ring, with no need to do anything on the pulsers and high voltage power suppliers. This approach can efficiently increase the injection efficiency which is demanding in the top-up injection mode adopted by many new facilities of synchrotron radiation.
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.
55126258
Design and Development of an Elliptically Polarized Undulator of Length 3.5 m for TPS
An elliptically polarized undulator of length 3.5 m and period length 48 mm (EPU48) is designed to fulfil experiments on spin-polarized PES and inelastic scattering at the Taiwan Photon Source (TPS). EPU48 would be used to produce variously polarized light in the soft X-ray spectral domain 0.4-1.5 keV. To achieve efficient mechanical performance and a high quality of photon source, a new manufacturing method by casting is adopted to fabricate a key component of the carriage of the undulator at National Synchrotron Radiation Research Center (NSRRC). We expect this approach to bestow advantages of decreased assembly error, increased rigidity and highly precise properties. Here we describe details of the design of the magnetic circuit and the mechanical design of the EPU48 based on this new concept of engineering construction. INTRODUCTION With electron energy 3 GeV and beam current 500 mA, Taiwan Photon Source (TPS) is a third-generation experimental facility for synchrotron radiation that is undergoing civil-engineering construction. Various insertion devices, including in vacuum undulators (IU), cryogenic permanent magnet undulators (CPMU), elliptically polarized undulators (EPU) and superconducting undulators (SU) that are being considered for installation into the new storage ring in the TPS commission stage, are being discussed and planned so as to equip the machine to produce great brilliance and intense light to fulfil multidisciplinary experimental requirements. For the undulators adopted at TPS, table 1 and figure 1 show the key parameters and spectral performance estimated with Spectra code [1]. Two EPU of Apple-II type providing all polarized modes for radiation in the soft X-ray spectral range will be built internally [2]. To achieve a high quality and a brilliant light source, the demands of a robust and highly precise mechanical carriage become the most significant subject. For the implementation of this device, various aspects include magnetic-force behaviour, the layout of the structural configuration, the assembly and component selection that require thorough consideration. The entire control instrumentation must otherwise be compatible with the EPCIS system. Here we discuss the recent development and design status of two sets of EPU48. Table 1: Specification of Insertion Devices Adopted at TPS Ee /GeV EPU48 IU22 IU22 U50 3 photon energy /keV HP 0.4-1.5 5-20 5-20 0.08-1.5
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.
122018234
Development trends for insertion devices of future synchrotron light sources
The in-vacuum undulator with a permanent magnet at room temperature is a mature technology and is widely used; with a short period length in a medium-energy facility, it can enhance photon brilliance in the hard x-ray region. A cryogenic permanent magnet has been investigated as an in-vacuum undulator; this undulator will become the best prospective device to satisfy the requirements of a photon source with great brilliance in the hard x-ray region. For the further hard x-ray region, a superconducting wiggler can provide great flux with a continuous spectrum, whereas a superconducting undulator will provide great brilliance with a discrete spectrum. High-temperature superconducting wires are highly promising for use in the development of superconducting undulators; unique algorithms for their development with an extremely short period in a small-magnet gap have been devised. Some out-of-vacuum planar undulators with special functions must also be fabricated to enable diverse applications in various light-source facilities. This article describes current and future developments for insertion devices in storage-ring and free-electron-laser facilities and discusses their feasibility for use therein.
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.
16596210
A Consistent treatment for pion form-factors in space - like and time - like regions
We write down some relevant matrix elements for the scattering and decay processes of the pion by considering a quark-meson vertex function. The pion charge and transition form factors $F_\pi$, $F_{\pi\gamma}$, and $F_{\pi\gamma^*}$ are extracted from these matrix elements using a relativistic quark model on the light-front. We found that, the form factors $F_\pi$ and $F_{\pi\gamma}$ in the space-like region agree well with experiment. Furthermore, the branching ratios of all observed decay modes of the neutral pion, that are related to the form factors $F_{\pi\gamma}$ and $F_{\pi\gamma^*}$ in the time-like region, are all consistent with the data as well. Additionally, $F_\pi$ in the time-like region, which deals with the nonvalence contribution, is also discussed.
119482056
Light front approach for heavy pentaquark transitions
Assuming the two diquark structure for the pentaquark state as advocated in the Jaffe-Wilczek model, there exist exotic parity-even anti-sextet and parity-odd triplet heavy pentaquark baryons. The theoretical estimate of charmed and bottom pentaquark masses is quite controversial and it is not clear whether the ground-state heavy pentaquark lies above or below the strong-decay threshold. We study the weak transitions of heavy pentaquark states using the light-front quark model. In the heavy quark limit, heavy-to-heavy pentaquark transition form factors can be expressed in terms of three Isgur-Wise functions: two of them are found to be normalized to unity at zero recoil, while the third one is equal to 1/2 at the maximum momentum transfer, in accordance with the prediction of the large-Nc approach or the quark model. Therefore, the light-front model calculations are consistent with the requirement of heavy quark symmetry. Numerical results for form factors and Isgur-Wise functions are presented. Decay rates of the weak decays Theta_b+ to Theta_c0 pi+ (rho+), Theta_c0 to Theta+ pi- (rho-), Sigma'_{5b}+ to Sigma'_{5c}0 pi+ (rho+) and Sigma'_{5c}0 to N_8+ pi- (rho-) with Theta_Q, 
Sigma'_{5Q} and N_8 being the heavy anti-sextet, heavy triplet and light octet pentaquarks, respectively, are obtained. For weakly decaying Theta_b+ and Theta_c0, the branching ratios of Theta_b+ to Theta_c0 pi+, Theta_c0 to Theta+ pi- are estimated to be at the level of 10^{-3} and a few percents, respectively.
1152504
Weak-field expansion for processes in a homogeneous background magnetic field
The weak-field expansion of the charged fermion propagator under a uniform magnetic field is studied. Starting from Schwinger's proper-time representation, we express the charged fermion propagator as an infinite series corresponding to different Landau levels. This infinite series is then reorganized according to the powers of the external field strength B. For illustration, we apply this expansion to $\stackrel{\ensuremath{\rightarrow}}{\ensuremath{\gamma}}\ensuremath{\nu}\overline{\ensuremath{\nu}}$ and $\stackrel{\ensuremath{\rightarrow}}{\ensuremath{\nu}}\ensuremath{\nu}\ensuremath{\gamma}$ decays, which involve charged fermions in the internal loop. The leading and subleading magnetic-field effects to the above processes are computed.
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.
118632651
Leading-twist light cone distribution amplitudes for p-wave heavy quarkonium states
In this paper, a study of light-cone distribution amplitudes for p-wave heavy quarkonium states are presented. Within the light-front framework, the leading twist light-cone distribution amplitudes, and their relevant decay constants, have some simple relations. These relations can be further simplified when the non-relativistic limit and the wave function as a function of relative momentum |~ κ | are taken into consideration. In addition, the κ⊥ integrations in the equations of LCDAs and ξ-moments can be completed analytically when the Gaussian-type wave function is considered. After fixing the parame- ters that appear in the wave function, the curves and the corresponding decay constants of the LCDAs are plotted and calculated for the charmonium and bottomonium states. The first three non-vanishing ξ-moments of the LCDAs are estimated and are consistent with those of other theoretical approaches.