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High gradient experiments on NLCTA accelerator structures
This paper presents new results of high-gradient studies performed on a 1.8 m traveling-wave accelerator section with detuned high-order deflecting modes. This structure was designed initially for studies of detuned structures and will be installed in the Next Linear Collider Test Accelerator (NLCTA). The paper describes the test set-up in the Accelerator Structure Test Area (ASTA) including electron gun, prebuncher, pre-accelerator, spectrometer, Faraday cups, 200 MW SLED-II power compression system, Magic-T type phase shifters and attenuators. Rf processing, detailed dark current analysis, radiation problems, and beam acceleration measurements are discussed
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.
Detrended fluctuation analysis as a statistical tool to monitor the climate
Detrended fluctuation analysis is used to investigate power law relationship
between the monthly averages of the maximum daily temperatures for different
locations in the western US. On the map created by the power law exponents, we
can distinguish different geographical regions with different power law
exponents. When the power law exponents obtained from the detrended fluctuation
analysis are plotted versus the standard deviation of the temperature
fluctuations, we observe different data points belonging to the different
climates, hence indicating that by observing the long-time trends in the
fluctuations of temperature we can distinguish between different climates.Comment: 8 pages, 4 figures, submitted to JSTA
Spectral Phase Control of Interfering Chirped Pulses for High-Energy Narrowband Terahertz Generation
Highly-efficient optical generation of narrowband terahertz (THz) radiation
enables unexplored technologies and sciences from compact electron acceleration
to charge manipulation in solids. State-of-the-art conversion efficiencies are
currently achieved using difference-frequency generation (DFG) driven by
temporal beating of chirped pulses but remain, however, far lower than desired
or predicted. Here we show that high-order spectral phase fundamentally limits
the efficiency of narrowband DFG using chirped-pulse beating and resolve this
limitation by introducing a novel technique based on tuning the relative
spectral phase of the pulses. For optical terahertz generation, we demonstrate
a 13-fold enhancement in conversion efficiency for 1%-bandwidth, 0.361 THz
pulses, yielding a record energy of 0.6 mJ and exceeding previous
optically-generated energies by over an order of magnitude. Our results prove
the feasibility of millijoule-scale applications like terahertz-based electron
accelerators and light sources and solve the long-standing problem of temporal
irregularities in the pulse trains generated by interfering chirped pulses.Comment: 25 pages, 5 figures, updated to the state before review at Nature
Communications (updated the affiliations, title, some content, methods, etc.
Improved limits on nuebar emission from mu+ decay
We investigated mu+ decays at rest produced at the ISIS beam stop target.
Lepton flavor (LF) conservation has been tested by searching for \nueb via the
detection reaction p(\nueb,e+)n. No \nueb signal from LF violating mu+ decays
was identified. We extract upper limits of the branching ratio for the LF
violating decay mu+ -> e+ \nueb \nu compared to the Standard Model (SM) mu+ ->
e+ nue numub decay: BR < 0.9(1.7)x10^{-3} (90%CL) depending on the spectral
distribution of \nueb characterized by the Michel parameter rho=0.75 (0.0).
These results improve earlier limits by one order of magnitude and restrict
extensions of the SM in which \nueb emission from mu+ decay is allowed with
considerable strength. The decay \mupdeb as source for the \nueb signal
observed in the LSND experiment can be excluded.Comment: 10 pages, including 1 figure, 1 tabl
Uncertain Climate Policy and the Green Paradox
Unintended consequences of announcing a climate policy well in advance of its implementation have been studied in a variety of situations. We show that a phenomenon akin to the so-called “Green-Paradox” holds also when the policy implementation date is uncertain. Governments are compelled, by international and domestic pressure, to demonstrate an intention to reduce greenhouse gas emissions. Taking actual steps, such as imposing a carbon tax on fossil energy, is a different matter altogether and depends on a host of political considerations. As a result, economic agents often consider the policy implementation date to be uncertain. We show that in the interim period between the policy announcement and its actual implementation the emission of green-house gases increases vis-à -vis business-as-usual
CLASH: z ~ 6 young galaxy candidate quintuply lensed by the frontier field cluster RXC J2248.7-4431
We present a quintuply lensed z ~ 6 candidate discovered in the field of the
galaxy cluster RXC J2248.7-4431 (z ~ 0.348) targeted within the Cluster Lensing
and Supernova survey with Hubble (CLASH) and selected in the deep HST Frontier
Fields survey. Thanks to the CLASH 16-band HST imaging, we identify the
quintuply lensed z ~ 6 candidate as an optical dropout in the inner region of
the cluster, the brightest image having magAB=24.81+-0.02 in the f105w filter.
We perform a detailed photometric analysis to verify its high-z and lensed
nature. We get as photometric redshift z_phot ~ 5.9, and given the extended
nature and NIR colours of the lensed images, we rule out low-z early type and
galactic star contaminants. We perform a strong lensing analysis of the
cluster, using 13 families of multiple lensed images identified in the HST
images. Our final best model predicts the high-z quintuply lensed system with a
position accuracy of 0.8''. The magnifications of the five images are between
2.2 and 8.3, which leads to a delensed UV luminosity of L_1600 ~ 0.5L*_1600 at
z=6. We also estimate the UV slope from the observed NIR colours, finding a
steep beta=-2.89+-0.38. We use singular and composite stellar population SEDs
to fit the photometry of the hiz candidate, and we conclude that it is a young
(age <300 Myr) galaxy with mass of M ~ 10^8Msol, subsolar metallicity
(Z<0.2Zsol) and low dust content (AV ~ 0.2-0.4).Comment: 21 pages, 13 figures, 6 tables, submitted to MNRAS on 11 Aug 2013,
accepted on 23 Nov 201
Soft X-Ray Projection Lithography Using a 1-1 Ring Field Optical-System
An iridium-coated Offner 1:1 ring field camera has been used to carry out projection lithography using 42 nm light from an undulator in the vacuum ultra violet storage ring at Brookhaven National Laboratory. Near-diffraction-limited resolution has been obtained showing features as small as 0.2-mu-m within a 2 mm x 0.25 mm image field. Images of both transmission and reflection masks have been obtained. The impact of source coherence on imagery has been investigated. Hydrocarbon contamination problems experienced in this photon energy range have been investigated and possible solutions are suggested
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