Characterisation of the PXIE Allison-type emittance scanner D׳Arcy, R.; Alvarez, M.; Gaynier, J. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
04/2016, Letnik:
815, Številka:
C
Journal Article
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An Allison-type emittance scanner has been designed for PXIE at FNAL with the goal of providing fast and accurate phase space reconstruction. The device has been modified from previous LBNL/SNS ...designs to operate in both pulsed and DC modes with the addition of water-cooled front slits. Extensive calibration techniques and error analysis allowed confinement of uncertainty to the <5% level (with known caveats). With a 16-bit, 1MHz electronics scheme the device is able to analyse a pulse with a resolution of 1μs, allowing for analysis of neutralisation effects. This paper describes a detailed breakdown of the R&D, as well as post-run analysis techniques.
We propose and demonstrate a nonintrusive diagnostic technique for measuring longitudinal bunch profiles of an operational high-power hydrogen ion (H−) beam in the Spallation Neutron Source (SNS) ...linear accelerator at Oak Ridge National Laboratory (ORNL). The technique consists of a laser wire formed by a picosecond pulsed laser beam and a virtual slit created by controlling the magnetic field of the electron detector. The virtual slit eliminates the influence of the transverse beam profile and size on the longitudinal bunch profile measurement. The effectiveness of the diagnostics is investigated first in numerical simulations followed by experimental demonstrations performed on the neutron production (1.4 MW on target)H−beam at the SNS superconducting linac. The results from the present measurement method are verified by an independent measurement approach.
We perform a comparison of different approaches to star-galaxy classification using the broad-band photometric data from Year 1 of the Dark Energy Survey.
We present the results of a search for gravitationally lensed giant arcs conducted on a sample of 825 SDSS galaxy clusters. Both a visual inspection of the images and an automated search were ...performed, and no arcs were found. This result is used to set an upper limit on the arc probability per cluster. We present selection functions for our survey, in the form of arc detection efficiency curves plotted as functions of arc parameters, for both the visual inspection and the automated search. The selection function is such that we are sensitive only to long, high surface brightness arcs with g-band surface brightness mu sub(g) less than or equal to 24.8 and length-to-width ratio l/w greater than or equal to 10. Our upper limits on the arc probability are compatible with previous arc searches. Finally, we report on a serendipitous discovery of a giant arc in the SDSS data, known inside the SDSS Collaboration as Hall's arc.
ABSTRACT
We present a blind time-delay cosmographic analysis for the lens system DES J0408−5354. This system is extraordinary for the presence of two sets of multiple images at different redshifts, ...which provide the opportunity to obtain more information at the cost of increased modelling complexity with respect to previously analysed systems. We perform detailed modelling of the mass distribution for this lens system using three band Hubble Space Telescope imaging. We combine the measured time delays, line-of-sight central velocity dispersion of the deflector, and statistically constrained external convergence with our lens models to estimate two cosmological distances. We measure the ‘effective’ time-delay distance corresponding to the redshifts of the deflector and the lensed quasar $D_{\Delta t}^{\rm eff}=$$3382_{-115}^{+146}$ Mpc and the angular diameter distance to the deflector Dd = $1711_{-280}^{+376}$ Mpc, with covariance between the two distances. From these constraints on the cosmological distances, we infer the Hubble constant H0= $74.2_{-3.0}^{+2.7}$ km s−1 Mpc−1 assuming a flat ΛCDM cosmology and a uniform prior for Ωm as $\Omega _{\rm m} \sim \mathcal {U}(0.05, 0.5)$. This measurement gives the most precise constraint on H0 to date from a single lens. Our measurement is consistent with that obtained from the previous sample of six lenses analysed by the H0 Lenses in COSMOGRAIL’s Wellspring (H0LiCOW) collaboration. It is also consistent with measurements of H0 based on the local distance ladder, reinforcing the tension with the inference from early Universe probes, for example, with 2.2σ discrepancy from the cosmic microwave background measurement.
After 30 years of operation, the Cockcroft-Walton based injector at the Fermi National Accelerator Laboratory has been replaced by a new beam line including a dimpled magnetron 35 keV source in ...combination with a 750 keV four-rod radio frequency quadrupole (RFQ). The new injector is followed by the existing drift tube linac. Prior to installation, a test beam line was built which included the magnetron source and the four-rod RFQ with a number of beam measurement instrumentation. The first beam test with the RFQ showed an output energy deviation greater than 2.5%. Other problems also showed up which led to investigations of the output energy, power consumption and transmission properties using rf simulations which were complemented with additional beam measurements. The sources of this deviation and the mechanical modifications of the RFQ to solve this matter will be presented in this paper. Meanwhile, the nominal output energy of 750 keV has been confirmed and the new injector with the four-rod RFQ is in full operation.
ABSTRACT
Determining the distribution of redshifts of galaxies observed by wide-field photometric experiments like the Dark Energy Survey (DES) is an essential component to mapping the matter density ...field with gravitational lensing. In this work we describe the methods used to assign individual weak lensing source galaxies from the DES Year 3 Weak Lensing Source Catalogue to four tomographic bins and to estimate the redshift distributions in these bins. As the first application of these methods to data, we validate that the assumptions made apply to the DES Y3 weak lensing source galaxies and develop a full treatment of systematic uncertainties. Our method consists of combining information from three independent likelihood functions: self-organizing map p(z) (sompz), a method for constraining redshifts from galaxy photometry; clustering redshifts (WZ), constraints on redshifts from cross-correlations of galaxy density functions; and shear ratios (SRs), which provide constraints on redshifts from the ratios of the galaxy-shear correlation functions at small scales. Finally, we describe how these independent probes are combined to yield an ensemble of redshift distributions encapsulating our full uncertainty. We calibrate redshifts with combined effective uncertainties of σ〈z〉 ∼ 0.01 on the mean redshift in each tomographic bin.
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