73528276
Temporal characteristics of a SASE FEL
We have performed a single-shot, time-resolved measurement of the output field of a SASE FEL using the frequency-resolved optical gating (FROG) technique. The measurement reveals the phase and the amplitude of the SASE output as functions of time and frequency, hence enables us to perform a full characterization of the SASE FEL output. We examined both the single-shot field evolution as well as the statistics over multiple shots on the phase and intensity evolution.
54683815
The optimization of a DC injector for the Energy Recovery Linac upgrade to APS
An energy recovery linac based light source is a potential revolutionary upgrade to the Advanced Photon Source (APS) at Argonne National Laboratory. The concept relies on several key research areas, one of which is the generation of ultra-low emittance, high-average-current electron beams. In this paper, we present our investigation of a dc-gun-based system for ultra-low emittance bunches in the 20 pC range. A parallel multi-objective numerical optimization is performed in multi-parameter space. Parameters varied include experimentally feasible drive-laser shapes, the DC gun voltage, the thermal energy of the emitted photo-electrons and other electric or magnetic field strengths, RF cavity phase etc. Our goal is to deliver a {approx}10 MeV, 20 pC bunch at the entrance of the linac with an emittance of 0.1 {micro}m or lower, rms bunch length of 2 {approx} 3 ps, and energy spread no larger than 140 keV. We present the machine parameters needed to generate such an injector beam, albeit without a merger.
37310101
DEVELOPMENT AND MEASUREMENT OF STRAIN FREE RF PHOTOINJECTOR VACUUM WINDOWS *
RF photoinjectors produce the highest brightness electron bunches only under nearly ideal illumination by a drive laser [1]. The vacuum window used to introduce the laser beam is an essential element that may potentially degrade the distribution, making it difficult or impossible to know the actual uniformity achieved at the cathode. Because of the necessity to obtain ultrahigh vacuum near the photoinjector, some restrictions are imposed on the fabrication technology available to manufacture distortion-free windows. At the UV wavelengths commonly used for photoinjectors, it is challenging to measure and eliminate degradation caused by vacuum windows. Here, we discuss the initial measurements of a strain-free, coated, UHV window manufactured by Insulator Seal in collaboration with members of Brookhaven and Argonne National Laboratories.
119342728
Deuteron Compton scattering in effective field theory : Spin-dependent cross sections and asymmetries
Polarized Compton scattering on the deuteron is studied in nuclear effective field theory. A set of tensor structures is introduced to define 12 independent Compton amplitudes. The scalar and vector amplitudes are calculated up to next-to-next-to-leading order in low-energy power counting. Significant contribution to the vector amplitudes is found to come from the spin-orbit type of relativistic corrections. A double-helicity-dependent cross section {delta}{sub 1}d{sigma}/d{omega}=(d{sigma}{sub +1-1}-d{sigma}{sub +1+1})/2d{omega} is calculated to the same order, and the effect of the nucleon isoscalar spin-dependent polarizabilities is found to be smaller than the effect of isoscalar spin-independent ones. Contributions of spin-independent polarizabilities are investigated in various asymmetries, one of which has an effect as large as 12% (26%) at the center-of-mass photon energy 30 (50) MeV.
119023320
Sum rules and spin-dependent polarizabilities of the deuteron in effective field theory
We construct sum rules for the forward vector and tensor polarizabilities for any spin-S target and apply them to the spin-1 deuteron. We calculate these polarizabilities of the deuteron to the next-to-leading order in the pionless effective field theory.
119494911
Deuteron Compton scattering in effective field theory and spin-independent nucleon polarizabilities
Abstract Deuteron Compton scattering is calculated to O ( Q 2 ) in pionless effective field theory using a dibaryon approach. The vector amplitude, which was not included in the previous pionless calculations, contributes to the cross section at O ( Q 2 ) and influences significantly the extracted values of nucleon electric polarizability at incident photon energy 49 MeV. We recommend future high precision deuteron Compton scattering experiments being performed at 25–35 MeV photon energy where the nucleon polarizability effects are appreciable and the pionless effective field theory is most reliable. For example, a measurement at 30 MeV with a 3% error will constrain the isoscalar nucleon electric polarizability α 0 with a ∼30% error.
120566938
Direct detection of hot dark matter in the form of active and sterile neutrinos
Both active and sterile sub-eV neutrinos can serve for hot dark matter (DM) in the Universe. We consider the beta-decaying (e.g., 3H) and EC-decaying (e.g., 163Ho) nuclei as the most promising targets to capture hot DM in the laboratory. We calculate the capture rates of relic electron neutrinos and antineutrinos against the corresponding beta decay or electron capture (EC) decay backgrounds in the (3+Ns) flavor mixing scheme. We stress that such direct measurements of hot DM might not be hopeless in the long term.
119183402
Exploring the full parameter space for an interacting dark energy model with recent observations including redshift-space distortions: Application of the parametrized post-Friedmann approach
Dark energy can modify the dynamics of dark matter if there exists a direct interaction between them. Thus a measurement of the structure growth, e.g., redshift-space distortions (RSD), can provide a powerful tool to constrain the interacting dark energy (IDE) models. For the widely studied $Q=3\beta H\rho_{de}$ model, previous works showed that only a very small coupling ($\beta\sim\mathcal{O}(10^{-3})$) can survive in current RSD data. However, all these analyses had to assume $w>-1$ and $\beta>0$ due to the existence of the large-scale instability in the IDE scenario. In our recent work [Phys. Rev. D 90, 063005 (2014)], we successfully solved this large-scale instability problem by establishing a parametrized post-Friedmann (PPF) framework for the IDE scenario. So we, for the first time, have the ability to explore the full parameter space of the IDE models. In this work, we reexamine the observational constraints on the $Q=3\beta H\rho_{de}$ model within the PPF framework. By using the Planck data, the baryon acoustic oscillation data, the JLA sample of supernovae, and the Hubble constant measurement, we get $\beta=-0.010^{+0.037}_{-0.033}$ ($1\sigma$). The fit result becomes $\beta=-0.0148^{+0.0100}_{-0.0089}$ ($1\sigma$) once we further incorporate the RSD data in the analysis. The error of $\beta$ is substantially reduced with the help of the RSD data. Compared with the previous results, our results show that a negative $\beta$ is favored by current observations, and a relatively larger interaction rate is permitted by current RSD data.