A simple method for the determination of the structure of ultrashort relativistic electron bunches

In this paper we propose a new method for measurements of the longitudinal profile of 100 femtosecond electron bunches for X-ray Free Electron Lasers (XFELs). The method is simply the combination of two well-known techniques, which where not previously combined to our knowledge. We use seed 10-ps 1047 nm quantum laser to produce exact optical replica of ultrafast electron bunches. The replica is generated in apparatus which consists of an input undulator (energy modulator), and the short output undulator (radiator) separated by a dispersion section. The radiation in the output undulator is excited by the electron bunch modulated at the optical wavelength and rapidly reaches 100 MW-level peak power. We then use the now-standard method of ultrashort laser pulse-shape measurement, a tandem combination of autocorrelator and spectrum (FROG -- frequency resolved optical gating). The FROG trace of the optical replica of electron bunch gives accurate and rapid electron bunch shape measurements in a way similar to a femtosecond oscilloscope. Real-time single-shot measurements of the electron bunch structure could provide significant information about physical mechanisms responsible for generation ultrashort electron bunches in bunch compressors. The big advantage of proposed technique is that it can be used to determine the slice energy spread and emittance in multishot measurements. It is possible to measure bunch structure completely, that is to measure peak current, energy spread and transverse emittance as a function of time. We illustrate with numerical examples the potential of the proposed method for electron beam diagnostics at the European X-ray FEL.Comment: 41 pages, 18 figure

Squeezed light generated by a microcavity laser

Includes bibliographical references (page 3326).Photon-number fluctuations 1.3 dB below the semiclassical shot-noise limit are observed in the output of a semiconductor microcavity laser. Although the laser oscillates in a single longitudinal mode, photon-number squeezed light is realized through nonclassical correlations between two orthogonally polarized, transverse laser modes

Emittance growth of a short electron bunch in circular motion

A short electron bunch undergoing circular motion produces space-charge forces that do not decrease with increasing bunch energy, unlike those induced by straight-line motion. These energy-independent forces can be separated into a noninertial space-charge force and a coherent synchrotron radiation force. These forces result in an energy spread in the bunch, and can lead to a potentially large emittance growth. These effects can take place in both (1) bunch compression systems used to increase the peak current and (2) the wiggler itself Numerical estimates of the emittance growth in a wiggler for a 1-ps long, 1-mm radius, 1-nC electron bunch can be as large as 0.1 {pi} mm mrad per wiggle period; the energy spread can grow as much as 30 keV per wiggle period. These types of beam quality degradation may become significant for future, short-wavelength free-electron lasers requiring high-brightness electron beams, especially for self-amplified spontaneous emission operation

Preliminary injector, accelerator, and beamline design for rf-linac-driven XUV free-electron lasers

The proposed Los Alamos National Laboratory XUV free-electron laser (FEL) facility requires exceptional beam quality at high peak currents. Although the beam quality needed for a demonstration machine lasing at 50 nm is not far from what can be expected with extensions of present linacs to higher energy, conventional injector technology will not meet the requirements needed for lasing at 12 or 4 nm. We have conceived a preliminary injector and accelerator design that will meet these requirements. Using the Los Alamos photoelectric injector, it appears that normalized 90% emittances of 24 ..pi.. dot mm dot mrad can be attained in a relatively straightforward manner, and emittances down to 4 ..pi.. doe mm dot mrad are possible. Beamline simulations have been performed with the particle-pushing code PARMELA, using particle-dump inputs from the particle-in-cell code ISIS. The latter models the photoelectric gun up to the range between 0.75 and 1 MeV. Designs including electron guns with Pierce geometries have also been studied. Using an injector with a large planar-cathode Pierce gun seems to satisfy the 50-nm lasing requirements. In addition, other beamline questions have been studied. Beamline bends have been designed that are achromatic and nearly isochronous. The threshold for cumulative beam breakup and the emittance growth caused by transverse resistive-wall beam instability have been calculated. Finally, we discuss the advantages and disadvantages of building a straight-line machine versus a recycling machine, including recycling instability current levels. 11 refs., 16 figs

Childhood intermittent and persistent rhinitis prevalence and climate and vegetation: A global ecologic analysis

Background: The effect of climate change and its effects on vegetation growth, and consequently on rhinitis,are uncertain.Objective: To examine between- and within-country associations of climate measures and the normalizeddifference vegetation index with intermittent and persistent rhinitis symptoms in a global context.Methods: Questionnaire data from 6- to 7-year-olds and 13- to 14-year-olds were collected in phase 3 of theInternational Study of Asthma and Allergies in Childhood. Associations of intermittent (>1 symptom reportbut not for 2 consecutive months) and persistent (symptoms for -2 consecutive months) rhinitis symptomprevalences with temperature, precipitation, vapor pressure, and the normalized difference vegetation indexwere assessed in linear mixed-effects regression models adjusted for gross national income and populationdensity. The mean difference in prevalence per 100 children (with 95% confidence intervals [CIs]) perinterquartile range increase of exposure is reported.Results: The country-level intermittent symptom prevalence was associated with several country-levelclimatic measures, including the country-level mean monthly temperature (6.09-C; 95% CI, 2.06e10.11-C per 10.4-C), precipitation (3.10 mm; 95% CI, 0.46e5.73 mm; per 67.0 mm), and vapor pressure(6.21 hPa; 95% CI, 2.17e10.24 hPa; per 10.4 hPa) among 13- to 14-year-olds (222 center in 94 countries).The center-level persistent symptom prevalence was positively associated with several center-level climaticmeasures. Associations with climate were also found for the 6- to 7-year-olds (132 center in 57countries).Conclusion: Several between- and within-country spatial associations between climatic factors and intermittentand persistent rhinitis symptom prevalences were observed. These results provide suggestive evidencethat climate (and future changes in climate) may influence rhinitis symptom prevalence

Estren promotes androgen phenotypes in primary lymphoid organs and submandibular glands

BACKGROUND: Estrogens and androgens have extensive effects on the immune system, for example they suppress both T and B lymphopoiesis in thymus and bone marrow. Submandibular glands are sexually dimorphic in rodents, resulting in larger granular convoluted tubules in males compared to females. The aim of the present experiments was to investigate the estrogenic and androgenic effects of 4-estren-3α,17β-diol (estren) on thymus, bone marrow and submandibular glands, and compare the effects to those of 17β-estradiol (E2) and 5α-dihydrotestosterone (DHT), respectively. Estrogen receptors (ERs) were blocked by treatment of mice with the ER-antagonist ICI 182,780; also, knock-out mice lacking one or both ERs were used. RESULTS: As expected, the presence of functional ERs was mandatory for all the effects of E2. Similar to DHT-treatment, estren-treatment resulted in decreased thymus weight, as well as decreased frequency of bone marrow B cells. Treatment with estren or DHT also resulted in a shift in submandibular glands towards an androgen phenotype. All the effects of estren and DHT were independent of ERs. CONCLUSION: Our study is the first to show that estren has similar effects as the androgen DHT on lymphopoiesis in thymus and bone marrow, and on submandibular glands, and that these effects are independent of estrogen receptors. This supports the hypothesis of estren being able to signal through the androgen receptor

CoSyR: a novel beam dynamics code for the modeling of synchrotron radiation effects

The self-consistent nonlinear dynamics of a relativistic charged particle beam interacting with its complete self-fields is a fundamental problem underpinning many of the accelerator design issues in high brightness beam applications, as well as the development of advanced accelerators. Particularly, synchrotron radiation induced effects in a magnetic dispersive beamline element can lead to collective beam instabilities and emittance growth. A novel beam dynamic code is developed based on a Lagrangian method for the calculation of the particles' radiation near-fields using wavefront/wavelet meshes via the Green's function of the Maxwell equations. These fields are then interpolated onto a moving mesh for dynamic update of the beam. This method allows radiation co-propagation and self-consistent interaction with the beam in the simulation at greatly reduced numerical errors. Multiple levels of parallelisms are inherent in this method and implemented in our code CoSyR to enable at-scale simulations of nonlinear beam dynamics on modern computing platforms using MPI, multi-threading, and GPUs. CoSyR has been used to evaluate the transverse and longitudinal coherent radiation effects on the beam and to investigate beam optics designs proposed for mitigation of beam brightness degradation in a magnetic bunch compressor. In this paper, the design of CoSyR, as well as the benchmark with other coherent synchrotron radiation models, are described and discussed.Comment: 17 pages, 14 figure