[en] It is well known that the electron beam emittance can be lowered by keeping positive dispersion in the insertion straight section of an otherwise double bend achromat lattice. But the fact that the beam size at the straight section is not simply determined by the emittance any more has made the scheme suspicious. There was even a claim that the minimum electron beam size in the straight section remains unchanged regardless of the dispersion. It is shown in this article that the electron beam size can really be decreased by the positive dispersion of the straight section. It is also shown that the minimum of σ²/β of the dispersive straight section is 0.64 of that of the minimum double bend achromat lattice

[en] The central property of the self-amplified spontaneous emission (SASE) free-electron laser (FEL) is its longitudinal and transverse coherence. It is possible to show by a simple three-dimensional time-dependent simulation that both the longitudinal and transverse coherence are maximal at the linear regime endpoint, not at the saturation point where the SASE microbunching saturates. (author)

[en] Effects of vibrations in a storage ring are described. For convenience, vibrational sources are categorized as internal and external sources depending on their locations. Internal sources are likely to cause a random vibration of magnets, and their effects on the motion of a circulating beam are described well by the conventional closed orbit amplification factor. External sources cause all or some magnets to vibrate in a coherent manner, and their effect on the beam motion requires separate treatment. In this paper, we discuss the effects of both internal and external vibrational sources on the motion of a stored beam in a storage ring. The results are applied to the Pohang Light Source (PLS) 2 GeV storage ring, currently under construction in Pohang, Korea. Some recent measurement results of the PLS storage ring floor vibration are also presented. (author)

[en] This paper describes the simulation of the global orbit feedback system using the singular value decomposition (SVD) method, the error minimization method, and the neural network method. Instead of facing unacceptable correction result raised occasionally in the SVD method, we choose the error minimization method for the global orbit feedback. This method provides minimum orbit errors while avoiding unacceptable corrections, and keeps the orbit within the dynamic aperture of the storage ring. We simulate the Pohang Light Source (PLS) storage ring using the Methodical Accelerator Design (MAD) code that generates the orbit distortions for the error minimization method and the learning data set for neural network method. In order to compare the effectiveness of the neural network method with others, a neural network is trained by the learning algorithm using the learning data set. The global response matrix with a minimum error and the trained neural network are used to the global orbit feedback system. The simulation shows that a selection of beam position monitors (BPMs) is very sensitive in the reduction of rms orbit distortions, and the random choice gives better results than any other cases. (author)

[en] The positive effect of the dispersive straight section to improve the brightness in the third-generation light source with a triple bend lattice is discussed. In order to evaluate the brightness performance of a non-achromat case, used is σx2/βx used is at the insertion straight center that reduces to the usual beam emittance in the achromat case. The derived minimum of σx2/βx in the non-achromat case is smaller than the minimum emittance of the achromat case, just as it happens in the double bend lattice

[en] Derived are simple and accurate formulas breaking down a measured beam lifetime into its partial lifetimes of Touschek and beam-gas scattering. They are useful as practical means, because the existing formulas for the two partial lifetimes often fail to give numerically accurate numbers due to the lack of accurate information of necessary parameters. However, the new formulas need only the measured data of beam lifetime and are as accurate as the lifetime measurement. Also derived is the polarization dependence of the beam lifetime, which can be used to estimate the degree of polarization

[en] In this paper we report the infrared to visible upconversion luminescence properties of Er"3"+/Yb"3"+ co-doped BaMoO_4 nanocrystals synthesized via microwave assisted sol–gel processing route. Structural, morphological and upconversion luminescence properties were investigated by X-ray diffraction (XRD), Transmission Electron Microscopy (TEM), UV–vis diffuse reflectance spectroscopy (UV–vis DRS) and Upconversion Photoluminescence spectra analysis. Results revealed that the oval shaped BaMoO_4 nanocrystals ranging in size from 40 to 60 nm having tetragonal scheelite crystal structure were obtained by sol–gel route. The infrared to visible upconversion luminescence has been investigated in Er"3"+/Yb"3"+ co-doped in BaMoO_4with different Yb"3"+ concentrations. Intense green upconversion emissions around 528, 550 nm, and red emission at 657 nm corresponding to the "2H_1_1_/_2, "4S_3_/_2, and "4F_9_/_2 transitions, respectively to the "4I_1_5_/_2 ground state were observed when excited by CW laser radiation at 980 nm. The green emissions were greatly enhanced after the addition of sensitizer (Yb"3"+ ions). The effect of Yb"3"+ on the upconversion luminescence intensity was analyzed and explained in terms of the energy transfer process based. The reported work establishes the understanding of molybdates as an alternative host material for upconversion luminescence. - Graphical abstract: Infrared to visible upconversion luminescence of Er"3"+/Yb"3"+ co-doped BaMoO_4 nanocrystals. - Highlights: • Nanocrystals were synthesized by microwave assisted sol–gel processing route. • Strong green emissions were observed in Er"3"+/Yb"3"+ co-doped BaMoO_4 nanocrystals. • Provides an insight on Upconversion luminescence properties of oxides host materials