119256536
Polarization switching demonstration using crossed-planar undulators in a seeded free-electron laser
Polarization switching of light sources is required over a wide spectral range to investigate the symmetry of matter. In this paper, we report the first experimental demonstration of the crossed-planar undulators technique at a seeded free-electron laser, which holds great promise for the full control and fast switching of the polarization of short-wavelength radiation. In the experiment, the polarization state of the coherent radiation at the secondharmonic of the seed laser is switched successfully. The experimental results confirm the theory and pave the way for applying the crossed-planar undulators technique for seeded x-ray free-electron lasers.
117846823
Chemical Constraints on the Oxygen Abundances in Jupiter and Saturn
We perform a comparative analysis of the chemical kinetics of CO and $\rm PH_3$ in Jupiter and Saturn to assess the full set of constraints available on the troposphere water abundance in the two giant planets. For carbon monoxide we employ both a widely used CO kinetic scheme from Yung et al, and a newly identified CO chemical scheme from Visscher and Moses. For $\rm PH_3$ chemical scheme, we use the same chemical scheme as in Visscher and Fegley. Yung's chemical scheme for CO yields a water enrichment of 0.95 - 23.0 times solar abundance on Jupiter, and an upper limit of 14.0 for Saturn. Visscher's chemical scheme in contrast produces a water enrichment of 0.24 - 2.6 times solar abundance in Jupiter, and for Saturn an upper limit for water enrichment of 8.0. From this scheme, which takes advantage of the most up-to-date kinetics, we preclude high water enrichments on Jupiter and Saturn, and show that the kinetics approach yields Jovian bulk abundance in which values of C/O elevated relative to solar are admissible. Our result is consistent with recent reinterpretation of Galileo Probe data in which Jupiter formed in a water-depleted portion of the protoplanetary disk (Mousis et al).
118693453
Nonintersecting Brownian motions on the unit circle. Part I: noncritical cases
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.
1122949
Considerations on Beam Quality Control in MIT X-Ray FEL
The x-ray FEL at MIT[1] is one example of a design for a new generation linac-based light source. Such a new machine requires very high quality electron beams. Besides the usual requirements on beam parameters such as emittance, energy spread, peak current, there are new challenges emerging in the design studies, e.g., the arrival timing of electron beam must reach precision below tens of femtoseconds level to ensure the laser seed overlaps the desired sections of electron bunch in the multiple-stage HGHG process. In this paper we report the progress on design optimization towards high quality and low sensitivity beams.
119534509
Measurement of the average local energy spread of electron beam via coherent harmonic generation
The local energy spread of electron beam is a very important parameter for high-gain free-electron lasers (FELs), especially the seeded FELs. Highly accurate measurement of the extremely small local energy spread is rather challenging. In this paper, a simple method to accurately measure the average local energy spread based on the coherent harmonic generation is proposed. A one-dimensional analytical estimation is given to show the principle of this method, and three-dimensional simulation codes have been used to verify the theory. This method has been demonstrated on the Shanghai deep ultraviolet FEL, and the results show that the average local energy spread is about only 1.2 keV at the exit of the 136 MeV linac, which agrees well with the numerical simulations.
8730506
High current, large aperture, low HOM, single crystal Nb 2.85GHz superconducting cavity
There is an increasing demand for high beam current, high radio-frequency (RF) power S-band cavities in existing and new accelerator projects, such as for a study of future electron-ion collider (eRHIC) and a very brilliant, broadband, teraherz coherent synchrotron radiation source (CRS). To achieve this goal, the RF cavities must be upgraded to a gap voltage of 1.5 MV in a limited space available in the machine with a high gradient superconducting cavity. At the present time there are no cavities and accessories designed to support the high beam currents of up to 10-100 mA and at the same time provide a high gap voltage at such a high S-band frequency. AMAC proposed a high current, large aperture, low HOM, single crystal Nb 2.85 GHz superconducting cavity with high RF power coupler and HOM absorber device.
119215029
Generating polarization controllable FELs at Dalian coherent light source
The property of the FEL polarization is of great importance to the user community. FEL pulses with ultra-high intensity and flexible polarization control ability will absolutely open up new scientific realms. In this paper, several polarizationcontrolapproachesare presentedto investigate the great potential on Dalian coherent light source, which is a government-approvednovel FEL user facility with the capability of wavelength continuously tunable in the EUV regime of 50 − 150 nm. The numerical simulations show that both circularly polarized FELs with highly modulating frequencyand 100 μJ levelpulse energycouldbe generated at Dalian coherent light source.
118275882
Longitudinal Beam Dynamics with Space Charge in an FEL Driver Accelerator
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.
92986025
COMMISSIONING OF THE SSRF BOOSTER
The SSRF Booster, designed to accelerate the electrons from 150MeV to 3.5GeV, is a FODO structure synchrotron with 180m circumference and 2Hz repetition rate. The commissioning of the SSRF booster from the LTB transfer line started on Sept. 30th evening, 2007, the first turns of beam in the booster was obtained in 20 hours. With about 60 hours effective commissioning effort, the electrons were accelerated to 3.5GeV on October 5th morning, 2007. And then the first 3.5GeV beam was extracted to BTS transfer line on October 30th, 2007. In this paper, the SSRF booster is introduced and its commissioning results are presented. INTRODUCTION Shanghai Synchrotron Radiation Facility (SSRF) is a 3rd generation light source, which consists of a 150MeV LINAC, a full energy booster synchrotron and a 20-DBA storage ring. It will provide 4nm·rad nature emittance electron beam at 3.5GeV [1][2]. SSRF booster is used to accelerate the electron beam from 150MeV to 3.5GeV. It is composed with 2 super periods, 28 standard FODO cells and 180m circumferences. The curvature radius of dipole is 14.515m, which can reduce the eddy currents effectively during the energy ramping. There are also eight 2.9m straight sections, which used for the installation of injection, extraction and radio frequency systems [3]. BOOSTER PARAMETERS Fig.1 shows layout of one standard booster cell. Fig.2 shows lattice functions in one quarter of the ring. Figure1: Layout of one standard booster cell. Figure 2: Twiss parameters of SSRF booster synchrotron. (One fourth of the ring is shown.). There are two modes, single bunch and multi bunch, designed for booster commissioning, which can satisfy both the accumulative rate and the top-up injection requirements of the storage ring. The main parameters of the booster are shown in Table 1. Table 1: Main Parameters of the Booster Parameters Value Energy range (GeV) 0.15~3.5 Single bunch 2 Current (mA) Multi bunch 15 Repetition rate (Hz) 2 Cell length (m) 6.4286 Length of long straight (m) 2.904 RF frequency (MHz) 499.654 Harmonic number 300 Nature emittance (nm·rad) 104 Tune, νH /νV 8.181/5.229 Natural chromaticity, ξH/ξV -9.91/-7.45 Nature energy spread 7.799×10 Momentum compaction, αP 0.01849 Damping time, τH,V,L (ms) 4.77/4.60/2.26 Longitudinal tune, νs 0.019 Bunch length (mm) 21.4 0 5 10 15 20 25 30 35 40 45 -5 0 5 10 15 20 25 30 s [m] β x ,y [m ] Twiss Parameters 0 5 10 15 20 25 30 35 40 45 0 0.2 0.4 0.6 0.8 1