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We present a calculation of the shot noise to be used as initial condition for the electron-beam phase-variables in numerical simulations of the free-electron laser.

We demonstrate analytically and numerically superradiant spiking behavior in the leading and trailing regions of a radiation pulse propagating within a long electron pulse in a single-pass, high-gain free-electron laser (FEL). A single superradiant spike is observed when the radiation pulse is shorter than a cooperation length L,. We show this work may be relevant to the understanding of the spiking behavior in the FEL oscillator, and to possible spiking mechanisms in a perturbed steady-state amplifier.

We report on the analysis of megahertz modulation of electrons as measured by the Shuttle Potential and Return Electron Experiment (SPREE) during dc firing of the shuttle electrodynamic tether system (SETS) fast pulsed electron generator (FPEG). The SPREE and FPEG were flown aboard the space shuttle Atlantis flight STS 46 as part of the Tethered SateRite System (TSS 1) mission. The principal data reported here are from the SPREE multiangular electrostatic analyzers (ESAs) and Space Particle Coprelator Experiment (SPACE). The ESAs, mounted on rotary tables, measured electrons and ions in the energy range from 10 eV to 10 keV over a solid angle of 2•r st. The SPACE is a signal processing system that analyzes the pulse stream from the SPREE ESAs to identify bunching of the electrons and ions produced by coherent wave-particle interactions (WPIs). The SPACE detects modulations in the electron fluxes in frequency range 0-to 10-MHz. This paper concerns 2-to 4-MHz modulations of the electron flux detected by the SPACE when the FPEG was firing in adc mode at pitch angles close to 90 ø. During such operations, FPEG emitted a current of 100 mA at an energy of I keV. For these times, electrons with energies from 10 to 1850 eV were measured by the SPREE. For energies between •10 and 100 eV the electron flux is basically isotropic. At higher energies the flux increases for pitch angles near 90 ø . The electron distribution functions generally decrease monotonically with increasing energy up to 100 eV. At energies > 100 eV the distributions either monotonically decrease or exhibit a peak or plateau at energies near the beam emission energy. Megahertz modulations were observed for electrons with energies from 10 to 1180 eV, on both positive and negative slopes in the distribution function and throughout the 2• sr sampled by the ESAs. The occurrence and strength of the modulations exhibit no clear dependence on the pitch angle at which the electrons are measured. However, they appear to be limited to low parallel velocities (( 3 x 10 • m s -•) where beam-generated waves are in resonance with suprathermal electrons. Paper number 95JA00679. 0148-0227/95/95JA-00679505.00 of the ambient thermal electrons [Hardy et al., 1995]. Since previous observations have shown that Coulomb scattering is a minor contributor to the interaction of the beam with the ambient environment [Wilhelm et al., 1985], wave-particle interactions (WPIs) with fast growth rates must contribute significantly to the production of these effects. In this paper we report evidence for strong WPIs in the form of megahertz modulations of electrons observed in the energy range from 10 eV to 1.2 keV. During previous beam-emission experiments wave sensors have detected both megahertz and kilohertz frequency signals. During Spacelab 1, Mourenas et al. [1989] reported strong waves at the harmonic of the electron tyrofrequency, n fee, closest to the upper hybrid frequency f-!,r. The Echo 7 sounding rocket measured beam-induced wave activity near f, hr at -..4.2 MHz [Ginet and...

Research at modern light sources continues to improve our knowledge of the natural world, from the subtle workings of life to matter under extreme conditions. Free-electron lasers, for instance, have enabled the characterization of biomolecular structures with sub-ångström spatial resolution, and paved the way to controlling the molecular functions. On the other hand, attosecond temporal resolution is necessary to broaden our scope of the ultrafast world. Here we discuss attosecond pulse generation beyond present capabilities. Furthermore, we review three recently proposed methods of generating attosecond x-ray pulses. These novel methods exploit the coherent radiation of microbunched electrons in undulators and the tailoring of the emitted wavefronts. The computed pulse energy outperforms pre-existing technologies by three orders of magnitude. Specifically, our simulations of the proposed Soft X-Ray Laser (SXL) at MAX IV (Lund, Sweden) show that a pulse duration of 50-100 attoseconds and a pulse energy up to 5 microjoules is feasible with the novel methods. In addition, the methods feature pulse shape control, enable the incorporation of orbital angular momentum, and can be used in combination with modern compact free-electron laser setups.

A recombinant strain of Aspergillus niger (B1-D), engineered to produce the marker protein hen egg white lysozyme, was investigated with regard to its susceptibility to "oxidative stress" in submerged culture in bioreactor systems. The culture response to oxidative stress, produced either by addition of exogenous hydrogen peroxide or by high-dissolved oxygen tensions, was examined in terms of the activities of two key defensive enzymes: catalase (CAT) and superoxide dismutase (SOD). Batch cultures in the bioreactor were generally found to have maximum specific activities of CAT and SOD (Umg x protein(-1)) in the stationary/early-decline phase. Continuous addition of H2O2 (16 mmole L(-1) h(-1)), starting in the early exponential phase, induced CAT but did not increase SOD significantly. Gassing an early exponential-phase culture with O2 enriched (25 vol%) air resulted in increased activities of both SOD and CAT relative to control processes gassed continuously with air, while gassing the culture with 25 vol% O2 enriched air throughout the experiment, although inducing a higher base level of enzyme activities, did not increase the maximum SOD activity obtained relative to control processes gassed continuously with air. The profile of the specific activity of SOD (U mg CDW(-1)) appeared to correlate with dissolved oxygen levels in processes where no H2O2 addition occurred. These findings indicate that it is unsound to use the term "oxidative stress" to encompass a stress response produced by addition of a chemical (H2O2) or by elevated dissolved oxygen levels because the response to each might be quite different.

Electron beam quality is paramount for X-ray pulse production in free-electron-lasers (FELs). State-of-the-art linear accelerators (linacs) can deliver multi-GeV electron beams with sufficient quality for hard X-ray-FELs, albeit requiring km-scale setups, whereas plasma-based accelerators can produce multi-GeV electron beams on metre-scale distances, and begin to reach beam qualities sufficient for EUV FELs. Here we show, that electron beams from plasma photocathodes many orders of magnitude brighter than state-of-the-art can be generated in plasma wakefield accelerators (PWFAs), and then extracted, captured, transported and injected into undulators without significant quality loss. These ultrabright, sub-femtosecond electron beams can drive hard X-FELs near the cold beam limit to generate coherent X-ray pulses of attosecond-Angstrom class, reaching saturation after only 10 metres of undulator. This plasma-X-FEL opens pathways for advanced photon science capabilities, such as unperturbed observation of electronic motion inside atoms at their natural time and length scale, and towards higher photon energies.