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.
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).
119232861
Phase-merging enhanced harmonic generation free-electron laser
Together with one of its variants, the recently proposed phase-merging enhanced harmonic generation (PEHG) free-electron laser (FEL) is systematically studied in this paper. Different from a standard high-gain harmonic generation scheme, a transverse gradient undulator is employed to introduce a phase-merging effect into the transversely dispersed electron beam in PEHG. The analytical theory of the phase-merging effect and the physical mechanism behind the phenomenon are presented. Using a representative set of beam parameters, intensive start-to-end simulations for soft x-ray FEL generation are given to illustrate the performance of PEHG. Moreover, some practical issues that may affect the performance of PEHG are also discussed.
17541739
Threshold error rates for the toric and surface codes
The surface code scheme for quantum computation features a 2d array of nearest-neighbor coupled qubits yet claims a threshold error rate approaching 1% (NJoP 9:199, 2007). This result was obtained for the toric code, from which the surface code is derived, and surpasses all other known codes restricted to 2d nearest-neighbor architectures by several orders of magnitude. We describe in detail an error correction procedure for the toric and surface codes, which is based on polynomial-time graph matching techniques and is efficiently implementable as the classical feed-forward processing step in a real quantum computer. By direct simulation of this error correction scheme, we determine the threshold error rates for the two codes (differing only in their boundary conditions) for both ideal and non-ideal syndrome extraction scenarios. We verify that the toric code has an asymptotic threshold of p = 15.5% under ideal syndrome extraction, and p = 7.8 10^-3 for the non-ideal case, in agreement with prior work. Simulations of the surface code indicate that the threshold is close to that of the toric code.
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.
18270897
Beam Physics Highlights of the FERMI@ELETTRA Project
The electron beam dynamics in the Fermi Linac has been studied in the framework of the design of a singlepass free electron laser (FEL) based on a seeded harmonic cascade. The wakefields of some accelerating sections represent a challenge for the preservation of a small beam emittance and for achieving a small final energy spread. Various analytical techniques and tracking codes have been employed in order to minimize the quadratic and the cubic energy chirps in the longitudinal phase space, since they may cause a degradation of the fel bandwidth. As for the transverse motion, the beam breakup (BBU) instability has been recognized as the main source of emittance dilution; the simulations show the validity of local and non-local correction methods in order to counteract the typical “banana” shape distortion of the beam caused by the instability.
1202782
DESIGN OPTIMIZATIONS OF X-RAY FEL FACILITY AT MIT
In recent years, a number of short wavelength FEL experiments have demonstrated key technologies and obtained good agreement between experiment and theory. 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 quality such as emittance, energy spread, peak current, etc., there are new challenges emerging in the design studies, e.g., the precise arrival timing of electron beam at lower tens of femtoseconds level to ensure the laser seed overlap 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. INTRODUCTIONS The proposed MIT x-ray laser incorporates design features that take advantage of many recent developments. It blends proven technologies into a powerful new instrument that combines the high power, coherence, and ultrashort timescale probe of a laser with the energy reach and spatial resolution of synchrotron x-rays. It is a primary goal to integrate the instruments and experimental methods from the laser and synchrotron radiation communities at the earliest stages of design. Integrated high-harmonic generation laser technology will seed the electron beam and generate photon beams with high longitudinal coherence and pulse lengths significantly below 100 femtoseconds, perhaps below 1 femtosecond. The FEL itself will use the high gain harmonic generation (HGHG) method to produce multiple harmonics of the tunable input seed. The output radiation has the full longitudinal and transverse coherence and stability of the seed laser, providing substantial improvement over performance based solely on SASE. A sketch of linac layout is shown in Figure 1. The major components are the superconducting electron linac of length ~300 m, plus undulator tunnels and experimental halls. The production of x-ray laser pulse begins with generation of the electron beam in the RF photoinjector. The photoelectrons are produced by a conventional laser striking the photocathode contained in a high field RF cavity, producing 200 pC to 1 nC pulses that are about 10 to 25 picoseconds long. The superconducting linac will accelerate electron beam to up to 4 GeV energy. At about 200 MeV and 900 MeV, the beam enters the first and second magnetic chicane, which compress the pulse length to between 100 to 1000 femtoseconds and increase the bunch current from a few tens of amps to a few thousand amps.
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.