In atmospheric and environmental sciences, optical spectrometers are used for the measurements of greenhouse gas mole fractions and the isotopic composition of water vapor or greenhouse gases. The ...large sample cell volumes (tens of milliliters to several liters) in commercially available spectrometers constrain the usefulness of such instruments for applications that are limited in sample size and/or need to track fast variations in the sample stream. In an effort to make spectrometers more suitable for sample-limited applications, we developed a low-volume analyzer capable of measuring mole fractions of methane and carbon monoxide based on a commercial cavity ring-down spectrometer. The instrument has a small sample cell (9.6 ml) and can selectively be operated at a sample cell pressure of 140, 45, or 20 Torr (effective internal volume of 1.8, 0.57, and 0.25 ml). We present the new sample cell design and the flow path configuration, which are optimized for small sample sizes. To quantify the spectrometer’s usefulness for sample-limited applications, we determine the renewal rate of sample molecules within the low-volume spectrometer. Furthermore, we show that the performance of the low-volume spectrometer matches the performance of the standard commercial analyzers by investigating linearity, precision, and instrumental drift.
X-shooter is the first 2nd generation instrument of the ESO Very Large Telescope(VLT). It is a very efficient, single-target, intermediate-resolution spectrograph that was installed at the Cassegrain ...focus of UT2 in 2009. The instrument covers, in a single exposure, the spectral range from 300 to 2500 nm. It is designed to maximize the sensitivity in this spectral range through dichroic splitting in three arms with optimized optics, coatings, dispersive elements and detectors. It operates at intermediate spectral resolution (R~4,000 - 17,000, depending on wavelength and slit width) with fixed echelle spectral format (prism cross-dispersers) in the three arms. It includes a 1.8"x4" Integral Field Unit as an alternative to the 11" long slits. A dedicated data reduction package delivers fully calibrated two-dimensional and extracted spectra over the full wavelength range. We describe the main characteristics of the instrument and present its performance as measured during commissioning, science verification and the first months of science operations.
When an ultrarelativistic electron traverses two closely spaced foils, a radiation spectrum ‘resonance’ appears, arising from the photon formation length extending from one foil, across the gap and ...into the second foil. Several theoretical approaches yield quite different answers to the spectral location of this ‘resonance’, and we have therefore in the CERN NA63 collaboration addressed the question experimentally with a 178 GeV electron beam. The experimental technique used – where a variable gap separates two thin gold foils – allows for a direct measurement of a length that is closely related to the distance over which the photon formation takes place. These are the first measurements to observe the gap dependence of the energy of the ‘resonance’ in the radiation spectrum from a structured target on a truly macroscopic scale up to 0.5 mm. The results are compared with the theory of Baier and Katkov, with both the modified and unmodified theories of Blankenbecler as well as with a naïve, straightforward expectation. Surprisingly, the experiment shows a clear preference for the two latter, comparatively unsophisticated, approaches.
A prototype of a luminometer, designed for a future
e
+
e
-
collider detector, and consisting at present of a four-plane module, was tested in the CERN PS accelerator T9 beam. The objective of this ...beam test was to demonstrate a multi-plane tungsten/silicon operation, to study the development of the electromagnetic shower and to compare it with MC simulations. The Molière radius has been determined to be 24.0 ± 0.6 (stat.) ± 1.5 (syst.) mm using a parametrization of the shower shape. Very good agreement was found between data and a detailed Geant4 simulation.
Eur. Phys. J. C 78 (2018) 135 A prototype of a luminometer, designed for a future e+e- collider detector,
and consisting at present of a four-plane module, was tested in the CERN PS
accelerator T9 ...beam. The objective of this beam test was to demonstrate a
multi-plane tungsten/silicon operation, to study the development of the
electromagnetic shower and to compare it with MC simulations. The Moli\`ere
radius has been determined to be 24.0 +/- 0.6 (stat.) +/- 1.5 (syst.) mm using
a parametrization of the shower shape. Very good agreement was found between
data and a detailed Geant4 simulation.
A prototype of a luminometer, designed for a future e+e- collider detector, and consisting at present of a four-plane module, was tested in the CERN PS accelerator T9 beam. The objective of this beam ...test was to demonstrate a multi-plane tungsten/silicon operation, to study the development of the electromagnetic shower and to compare it with MC simulations. The Molière radius has been determined to be 24.0 +/- 0.6 (stat.) +/- 1.5 (syst.) mm using a parametrization of the shower shape. Very good agreement was found between data and a detailed Geant4 simulation.
A prototype of a luminometer, designed for a future $e^+ e^−$ collider detector, and consisting at present of a four-plane module, was tested in the CERN PS accelerator T9 beam. The objective of this ...beam test was to demonstrate a multi-plane tungsten/silicon operation, to study the development of the electromagnetic shower and to compare it with MC simulations. The Molière radius has been determined to be 24.0 ± 0.6 (stat.) ± 1.5 (syst.) mm using a parametrization of the shower shape. Very good agreement was found between data and a detailed Geant4 simulation.
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