115963731
Development of a highly pixelated direct charge sensor, Topmetal-I, for ionizing radiation imaging
Using industrial standard 0.35{\mu}m CMOS Integrated Circuit process, we realized a highly pixelated sensor that directly collects charge via metal nodes placed on the top of each pixel and forms two dimensional images of charge cloud distribution. The first version, Topmetal-I, features a 64x64 pixel array of 80{\mu}m pitch size. Direct charge calibration reveals an average capacitance of 210fF per pixel. The charge collection noise is near the thermal noise limit. With the readout, individual pixel channels exhibit a most probable equivalent noise charge of 330e-.
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
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.
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.
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.
21579776
Mechanical induced beam motion in SRRC storage ring
It has been observed that the mechanical stability of some magnets had an influence on the closed orbit in the storage ring. In this paper, a mechanical shaker at a low vibration level was applied to the quadrupole magnet. The perturbation of the closed orbit was measured. The thermal induced distortion of magnet supporting structure was discussed. The motion of the BPM and quadrupole magnet were measured. Some examples of mechanical induced beam motion are discussed.
9083411
Improved analysis for the baryon masses to order Lambda(QCD) / m(Q) from QCD sum rules
We use the QCD sum rule approach to calculate the masses of the Lambda_Q and Sigma_Q baryons to the Lambda_{QCD}/m_Q order within the framework of heavy quark effective theory. We compare the direct approach and the covariant approach to this problem. Two forms of currents have been adopted in our calculation and their effects on the results are discussed. Numerical results obtained in both direct and covariant approaches are presented. The splitting between spin 1/2 and 3/2 doublets derived from our calculation is {\Sigma_Q^*}^2-\Sigma_Q^2\simeq 0.35\pm 0.03 GeV^2 which is in good agreement with the experiment.
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.
121216453
Heavy quark effective theory sum rules for higher excited charmed mesons: With a view on D(sJ)(2632)
Mass of the excited (1{sup -},2{sup -}) (2{sup -},3{sup -}) and (2{sup +},3{sup +}) cs states is calculated to the 1/m{sub Q} order within the framework of the heavy quark effective theory using QCD sum rule method. The obtained kinetic energy is comparable to the c-quark mass, thus results in large 1/m{sub Q} correction for the c-quark case. With the sum rules for the chromomagnetic interaction term, the mass splitting for the three doublets is presented. Based on the predicted mass spectrum the exotic D{sub sJ}(2632) state, if really exists, is unlikely to be a conventional orbitally higher excited cs state, although the experimental center lies within the range for the mass of the 1{sup -} meson.
55527280
Electron beam instrumentation techniques using coherent radiation
Much progress has been made on coherent radiation research since coherent synchrotron radiation was first observed in 1989. The use of coherent radiation as a bunch length diagnostic tool has been studied by several groups. In this paper, brief introductions to coherent radiation and far-infrared measurement are given, the progress and status of their beam diagnostic application are reviewed, different techniques are described, and their advantages and limitations are discussed.