Investigation of a 2-Colour Undulator FEL Using Puffin

Initial studies of a 2-colour FEL amplifier using one monoenergetic electron beam are presented. The interaction is modelled using the unaveraged, broadband FEL code Puffin. A series of undulator modules are tuned to generate two resonant frequencies along the FEL interaction and a self-consistent 2-colour FEL interaction at widely spaced non-harmonic wavelengths at 1nm and 2.4nm is demonstrated.Comment: Submitted to The 35th International Free-Electron Laser Conference, Manhattan, New York (2013

Microbial reduction of iron and porewater biogeochemistry in acidic peatlands

International audienceTemporal drying of upper soil layers of acidic methanogenic peatlands might divert the flow of reductants from CH4 formation to other electron-accepting processes due to a renewal of alternative electron acceptors. In this study, we evaluated the in situ relevance of Fe(III)-reducing microbial activities in peatlands of a forested catchment that differed in their hydrology. Intermittent seeps reduced sequentially nitrate, Fe(III), and sulfate during periods of water saturation. Due to the acidic soil conditions, released Fe(II) was transported with the groundwater flow and accumulated as Fe(III) in upper soil layers of a lowland fen apparently due to oxidation. Microbial Fe(III) reduction in the upper soil layer accounted for 26.7 and 71.6% of the anaerobic organic carbon mineralization in the intermittent seep and the lowland fen, respectively. In an upland fen not receiving exogenous Fe, Fe(III) reduction contributed only to 6.7%. Fe(II) and acetate accumulated in deeper porewater of the lowland fen with maximum concentrations of 7 and 3 mM, respectively. Both supplemental glucose and acetate stimulated the reduction of Fe(III) indicating that fermentative, incomplete, and complete oxidizers were involved in Fe(II) formation in the acidic fen. Amplification of DNA yielded PCR products specific for Acidiphilium-, Geobacter-, and Geothrix-, but not for Shewanella- or Anaeroromyxobacter-related sequences. Porewater biogeochemistry observed during a 3-year-period suggests that increased drought periods and subsequent intensive rainfalls due to global climate change will further favor Fe(III) and sulfate as alternative electron acceptors due to the storage of their reduced compounds in the soil

Design considerations for table-top, laser-based VUV and X-ray free electron lasers

A recent breakthrough in laser-plasma accelerators, based upon ultrashort high-intensity lasers, demonstrated the generation of quasi-monoenergetic GeV-electrons. With future Petawatt lasers ultra-high beam currents of ~100 kA in ~10 fs can be expected, allowing for drastic reduction in the undulator length of free-electron-lasers (FELs). We present a discussion of the key aspects of a table-top FEL design, including energy loss and chirps induced by space-charge and wakefields. These effects become important for an optimized table-top FEL operation. A first proof-of-principle VUV case is considered as well as a table-top X-ray-FEL which may open a brilliant light source also for new ways in clinical diagnostics.Comment: 6 pages, 4 figures; accepted for publication in Appl. Phys.

Doors

Staunch sentries of decision gloating and imposing tempting and untrustworthy. ~excerpt from poe

Jack in the Box

Behold the bloodless puppet rising out a cheap quadrangular man-hole. Fluorescent mandarin hair forming a deceptive heart around alabaster skin, framing his daisy petal eyes, his pink colossal nose, and boomerang mouth. ~excerpt from poe

Si-compatible candidates for high-K dielectrics with the Pbnm perovskite structure

We analyze both experimentally (where possible) and theoretically from first-principles the dielectric tensor components and crystal structure of five classes of Pbnm perovskites. All of these materials are believed to be stable on silicon and are therefore promising candidates for high-K dielectrics. We also analyze the structure of these materials with various simple models, decompose the lattice contribution to the dielectric tensor into force constant matrix eigenmode contributions, explore a peculiar correlation between structural and dielectric anisotropies in these compounds and give phonon frequencies and infrared activities of those modes that are infrared-active. We find that CaZrO_3, SrZrO_3, LaHoO_3, and LaYO_3 are among the most promising candidates for high-K dielectrics among the compounds we considered.Comment: 17 pages, 9 figures, 4 tables. Supplementary information: http://link.aps.org/supplemental/10.1103/PhysRevB.82.064101 or http://www.physics.rutgers.edu/~sinisa/highk/supp.pd

Beyond the required LISA free-fall performance: new LISA pathfinder results down to 20 μHz

In the months since the publication of the first results, the noise performance of LISA Pathfinder has improved because of reduced Brownian noise due to the continued decrease in pressure around the test masses, from a better correction of noninertial effects, and from a better calibration of the electrostatic force actuation. In addition, the availability of numerous long noise measurement runs, during which no perturbation is purposely applied to the test masses, has allowed the measurement of noise with good statistics down to 20  μHz. The Letter presents the measured differential acceleration noise figure, which is at (1.74±0.05)  fm s^{-2}/sqrt[Hz] above 2 mHz and (6±1)×10  fm s^{-2}/sqrt[Hz] at 20  μHz, and discusses the physical sources for the measured noise. This performance provides an experimental benchmark demonstrating the ability to realize the low-frequency science potential of the LISA mission, recently selected by the European Space Agency

Sub-femto-g free fall for space-based gravitational wave observatories: LISA pathfinder results

We report the first results of the LISA Pathfinder in-flight experiment. The results demonstrate that two free-falling reference test masses, such as those needed for a space-based gravitational wave observatory like LISA, can be put in free fall with a relative acceleration noise with a square root of the power spectral density of 5.2 ± 0.1 fm s−2/√Hz or (0.54 ± 0.01) × 10−15 g/√Hz, with g the standard gravity, for frequencies between 0.7 and 20 mHz. This value is lower than the LISA Pathfinder requirement by more than a factor 5 and within a factor 1.25 of the requirement for the LISA mission, and is compatible with Brownian noise from viscous damping due to the residual gas surrounding the test masses. Above 60 mHz the acceleration noise is dominated by interferometer displacement readout noise at a level of (34.8 ± 0.3) fm/√Hz, about 2 orders of magnitude better than requirements. At f ≤ 0.5 mHz we observe a low-frequency tail that stays below 12 fm s−2/√Hz down to 0.1 mHz. This performance would allow for a space-based gravitational wave observatory with a sensitivity close to what was originally foreseen for LISA

The LISA pathfinder mission

ISA Pathfinder (LPF), the second of the European Space Agency's Small Missions for Advanced Research in Technology (SMART), is a dedicated technology validation mission for future spaceborne gravitational wave detectors, such as the proposed eLISA mission. LISA Pathfinder, and its scientific payload - the LISA Technology Package - will test, in flight, the critical technologies required for low frequency gravitational wave detection: it will put two test masses in a near-perfect gravitational free-fall and control and measure their motion with unprecedented accuracy. This is achieved through technology comprising inertial sensors, high precision laser metrology, drag-free control and an ultra-precise micro-Newton propulsion system. LISA Pathfinder is due to be launched in mid-2015, with first results on the performance of the system being available 6 months thereafter. The paper introduces the LISA Pathfinder mission, followed by an explanation of the physical principles of measurement concept and associated hardware. We then provide a detailed discussion of the LISA Technology Package, including both the inertial sensor and interferometric readout. As we approach the launch of the LISA Pathfinder, the focus of the development is shifting towards the science operations and data analysis - this is described in the final section of the paper