119222591
Simulation studies on laser pulse stability for Dalian coherent light source
Dalian Coherent Light Source will use a 300 MeV LINAC to produce fully coherent photon pulses in the wavelength range between 150-50 nm by high gain harmonic generation free electron laser (FEL) scheme. To generate stable FEL pulses, a stringent tolerance budget is required for the LINAC output parameters, such as the mean beam energy stability, electron bunch arrival time jitter, peak current variation and the transverse beam position offset. In order to provide guidance for the design of the Dalian Coherent Light Source, in this paper, the sensitivity of FEL pulse energy fluctuation to various error sources of the electron bunch was performed using intensive start-to-end FEL simulations.
26749894
Compensating the electron beam energy spread by the natural transverse gradient of laser undulator in all-optical x-ray light sources.
All-optical ideas provide a potential to dramatically cut off the size and cost of x-ray light sources to the university-laboratory scale, with the combination of the laser-plasma accelerator and the laser undulator. However, the large longitudinal energy spread of the electron beam from laser-plasma accelerator may hinder the way to high brightness of these all-optical light sources. In this paper, the beam energy spread effect is proposed to be significantly compensated by the natural transverse gradient of a laser undulator when properly transverse-dispersing the electron beam. Theoretical analysis and numerical simulations on conventional laser-Compton scattering sources and high-gain all-optical x-ray free-electron lasers with the electron beams from laser-plasma accelerators are presented.
73648727
Polarization control proposal for Shanghai deep ultraviolet free electron laser
In this paper, a fully coherent radiation option with controllable polarization is proposed for the Shanghai deep ultraviolet free electron laser (FEL) test facility. Intensive start-to-end simulation suggests that the two crossed planar undulators which generate the horizontal and vertical linear polarized FEL, should be placed as close as possible for avoiding the polarization performance degradation of the final combined FEL radiation. With the existence of the phase-shifter between the two crossed radiators. Fourier-Transform-Limited output radiation with 100 nJ order pulse energy, 5 Ps full pulse length and circular polarization degree above 90% could be achieved. (C) 2012 Elsevier B.V. All rights reserved.
118693453
Nonintersecting Brownian motions on the unit circle. Part I: noncritical cases
119272921
Single-shot measurement of free-electron laser polarization at SDUV-FEL
In this paper, a division-of-amplitude photopolarimeter (DOAP) for measuring the polarization state of a free-electron laser (FEL) pulse is described. The incident FEL beam is divided into four separate beams, and four Stokes parameters can be measured in a single-shot. In the crossed-planar undulators experiment at the Shanghai deep ultraviolet FEL test facility, this DOAP instrument constructed in house responsed accurately and timely while the polarization-state of fully coherent FEL pulses were switched, which is helpful for confirming the crossed-planar undulators technique for short-wavelength FELs.
119212313
FEL Polarization Control Studies on Dalian Coherent Light Source
The polarization switch of a free-electron laser (FEL) is of great importance to the user scientific community. In this paper, we investigate the generation of controllable polarization FEL from two well-known approaches for Dalian coherent light source, i.e., crossed planar undulator and elliptical permanent undulator. In order to perform a fair comparative study, a one-dimensional time-dependent FEL code has been developed, in which the imperfection effects of an elliptical permanent undulator are taken into account. Comprehensive simulation results indicate that the residual beam energy chirp and the intrinsic FEL gain may contribute to the degradation of the polarization performance for the crossed planar undulator. And the elliptical permanent undulator is not very sensitive to the undulator errors and beam imperfections. Meanwhile, with proper configurations of the main planar undulators and additional elliptical permanent undulator section, circular polarized FEL with pulse energy exceeds 100 μJ could be achieved at Dalian coherent light source.
118902003
Tau/charm Factory collider design at BEPC
Main goals and parameters of the design of the Beijing tau‐charm factory (τcF) are presented. Three schemes, the standard, the monochromator and the crossing angle scheme, are implemented into one versatile lattice. In addition, a beam polarization scheme is discussed. Some systems of the factory are briefly described.
124156903
Dynamical Symmetry Breaking for Weinberg–Salam Model and Restoration at Finite Temperature
In this paper, we utilize Nambu-Jona-Lasinio (NJL) mechanism to discuss the dynamical symmetry breaking for Weinberg-Salam model. In the NJL mechanism the symmetry breaking not only is determined by the potential of scalar field but also has important relation with condensate of the fermion pair . We find that the coefficient of quadric term of scalar field can still cause symmetry breaking by virtue of , and the vacuum expected value of scalar field obeys , i.e., the order parameter which causes phase transition is the condensate of fermion pair . We also discuss the restoration problem of gauge symmetry breaking by the NJL mechanism at high temperatures.
119090605
Choice of heavy baryon currents in QCD sum rules
In this paper we investigate the effects due to the mixing of two interpolating currents for ground state baryons within the framework of Heavy Quark Effective Theory using the QCD sum rule approach. Both two-point and three-point sum rules, thus the mass, coupling constant and Isgur-Wise function sum rules are considered. It is interesting to contrast those results with each other. Based on the Isgur-Wise functions obtained in this paper, we also analyze the effects of current mixing to Lambda-type and and Sigma-type semi-leptonic decays Lambda_b-->Lambda_c\ell\bar\nu, \Sigma_b-->\Sigma_c\ell\bar\nu and \Sigma_b-->\Sigma^*_c\ell\bar\nu. Decay widths corresponding to various mixing parameters are obtained and can be compared to the experimental data.
18360781
FERMI@ELETTRA: A SEEDED FEL FACILITY FOR EUV AND SOFT X- RAYS
We describe the conceptual design and major performance parameters for the FERMI@Elettra Free Electron Laser (FEL) project funded for construction at Sincrotrone Trieste, Italy. This user facility complements the existing storage ring light source at Sincrotrone Trieste, and will be the first facility to be based on seeded harmonic cascade FELs. Seeded FELs provide high peak power pulses, with controlled temporal duration of the coherent output allowing tailored x-ray output for time domain explorations with short pulses of 100 fs or less, and high resolution with output bandwidths of the order of meV. The facility uses the existing 1.2 GeV S-band linac, driven by electron beam from a new highbrightness RF photocathode gun, and will provide tunable output over a range from ~100 nm to ~10 nm, and APPLE undulator radiators allow control of x-ray polarization. Initially, two FEL cascades are planned, a single-stage harmonic generation to operate over ~100 nm to ~40 nm, and a two-stage cascade operating from ~40 nm to ~10 nm or shorter wavelengh, each with spatially and temporally coherent output, and peak power in the GW range.
2277847
OPTIMIZATION AND MODELING OF THE ACCELERATOR FOR THE FERMI @ ELETTRA FEL
Design studies are in progress to use the existing FERMI{at}Elettra linear accelerator for a seeded harmonic cascade free-electron laser (FEL) facility [1]. This accelerator will be upgraded to 1.2 GeV and equipped with a low-emittance RF photocathode gun, laser heater, two bunch compressors, and a beam delivery system. We present an optimization study of all the components downstream of the gun, aimed at achieving the high peak current, low energy spread and low emittance electron beam necessary for the FEL. Various operational scenarios are discussed. Results of accelerator simulations including effects of space charge, coherent synchrotron radiation and wakefields are reported.