123166326
Electron transport theory in gases: must it be so difficult?
Abstract This article reviews recent progress in both experimental and kinetic theoretical determination of charged particle transport coefficients in electric and magnetic fields in the context of wire gas chamber detectors. The “Magboltz” code of Biagi [13] is discussed. It is pointed out that there is really no alternative to the accurate “multiterm theory” of Ness [3–5] if high precision is required, but this may not be readily accessible to the nonspecialist because of its mathematical complexity. On the other hand, “momentum transfer” theory provides relatively simple expressions for transport coefficients and has an accuracy of the order of 10%. We focus on this simplified theory in the bulk of the paper, discussing some previous results and giving new formulas. In order to illustrate the utility of the method, we have performed numerical calculations in several cases of relevance to wire gas chambers.
124862478
BUNCH COMPRESSION MONITOR
The longitudinal charge distribution in the electron bunches has a strong impact on the lasing process in a Free-Electron Laser based on the principle of Self Amplified Spontaneous Emission of radiation. For the ultraviolet and soft X ray FEL FLASH at DESY, structures in the range of ten to hundred micrometers play a crucial role. The investigation of the longitudinal charge distribution in the electron bunches on a bunch-by-bunch basis is an important issue for optimizing the bunch compression and improving the performance of the machine. This paper introduces a new tool for longitudinal diagnostics based on THz spectroscopy of coherent radiation. A novel spectrometer has been designed which permits to analyze the radiation of single electron bunches in a broad spectral range and with high resolution. Preliminary measurements with this spectrometer are presented. A strong variation of the CTR intensity in the 40 μm regime is observed when the off-crest phase in the accelerating cavities preceding the first magnetic bunch compressor is changed in small steps. This variation in the CTR intensity is found to be correlated with a similar variation in the pulse energy of the FEL light. Hence the THz spectrometer appears to be a very sensitive device for controlling the parameters of the bunch compression scheme.
119297111
HATSouth: A Global Network of Fully Automated Identical Wide-Field Telescopes*
HATSouth is the world's first network of automated and homogeneous telescopes that is capable of year-round 24 hr monitoring of positions over an entire hemisphere of the sky. The primary scientific goal of the network is to discover and characterize a large number of transiting extrasolar planets, reaching out to long periods and down to small planetary radii. HATSouth achieves this by monitoring extended areas on the sky, deriving high precision light curves for a large number of stars, searching for the signature of planetary transits, and confirming planetary candidates with larger telescopes. HATSouth employs six telescope units spread over three prime locations with large longitude separation in the southern hemisphere (Las Campanas Observatory, Chile; HESS site, Namibia; Siding Spring Observatory, Australia). Each of the HATSouth units holds four 0.18 m diameter f/2.8 focal ratio telescope tubes on a common mount producing an 8.2° × 8.2° field of view on the sky, imaged using four 4 K × 4 K CCD cameras and Sloan r filters, to give a pixel scale of 3.7'' pixel-1. The HATSouth network is capable of continuously monitoring 128 square arc degrees at celestial positions moderately close to the anti-solar direction. We present the technical details of the network, summarize operations, and present detailed weather statistics for the three sites. Robust operations have meant that on average each of the six HATSouth units has conducted observations on ~500 nights over a 2 years time period, yielding a total of more than 1 million science frames at a 4 minute integration time and observing ~10.65 hr day-1 on average. We describe the scheme of our data transfer and reduction from raw pixel images to trend-filtered light curves and transiting planet candidates. Photometric precision reaches ~6 mmag at 4 minute cadence for the brightest non-saturated stars at r ≈ 10.5. We present detailed transit recovery simulations to determine the expected yield of transiting planets from HATSouth. We highlight the advantages of networked operations, namely, a threefold increase in the expected number of detected planets, as compared to all telescopes operating from the same site.
123101687
Luminosity determination at HERA-B
Abstract A detailed description of an original method used to measure the luminosity accumulated by the HERA-B experiment for a data sample taken during the 2002–2003 HERA running period is reported. We show that, with this method, a total luminosity measurement can be achieved with a typical precision, including overall systematic uncertainties, at a level of 5% or better. We also report evidence for the detection of δ -rays generated in the target and comment on the possible use of such delta rays to measure luminosity.
55568152
Ultrabroadband terahertz source and beamline based on coherent transition radiation
Coherent transition radiation (CTR) in the THz regime is an important diagnostic tool for analyzing the temporal structure of the ultrashort electron bunches needed in ultraviolet and x-ray free-electron lasers. It is also a powerful source of such radiation, covering an exceptionally broad frequency range from about 200 GHz to 100 THz. At the soft x-ray free-electron laser FLASH we have installed a beam transport channel for transition radiation (TR) with the intention to guide a large fraction of the radiation to a laboratory outside the accelerator tunnel. The radiation is produced on a screen inside the ultrahigh vacuum beam pipe of the linac, coupled out through a diamond window and transported to the laboratory through an evacuated tube equipped with five focusing and four plane mirrors. The design of the beamline has been based on a thorough analysis of the generation of TR on metallic screens of limited size. The optical propagation of the radiation has been computed taking into account the effects of near-field (Fresnel) diffraction. The theoretical description of the TR source is presented in the first part of the paper, while the design principles and the technical layout of the beamline are described in the second part. First experimental results demonstrate that the CTR beamline covers the specified frequency range and preserves the narrow time structure of CTR pulses emitted by short electron bunches.
119881774
Anisotropic low energy electron collision cross sections for methane derived from transport coefficients
Based on a comprehensive set of transport parameters of electrons in methane derived from single electron spectra in the range of field 0.01-15 Td the authors determined a set of elastic and inelastic scattering cross sections up to 3 eV. The necessity to include anisotropic elastic scattering in a Boltzmann analysis of methane is demonstrated. In addition the drift velocity in a mixture of methane with helium was used to enhance the reliability of the derived cross sections. The low energy part of the cross sections for elastic scattering is subject to a MERT analysis and is compared with total cross section data from single scattering experiments.
2664921
Test Station for the CARIOCA FE-chip of the LHCb Muon Detector
This document describes the hardware and the software of a Front-End Electronics Test Station developed to test and characterize the Front-End ASIC for the LHCb Muon chambers. This ASIC, an 8-channel amplifier, shaper and discriminator with baseline restoration, processes read-out signals generated by Multi-Wire Proportional and GEM chambers located in a high radiation environment. It is almost entirely analog. In total, an amount of about 25000 chips will be produced in both the engineering and production runs. They will require individual testing, before final assembly on printed circuit boards. The test system we present has the following features: variable and bipolar charge injection, custom read-out, rate and time measuring circuitry, power consumption control, data analysis and statistical tools. The system is controlled by a LabVIEW based program. We present the results of about 3000 tests of ASIC produced in the engineering run.
2076811
Formation of the Black Hole in Nova Scorpii
Israelian and coworkers showed that the stellar companion of the black hole binary Nova Sco is polluted with material ejected in the supernova that accompanied the formation of the black hole primary. Here we systematically investigate the implications of these observations for the black hole formation process. Using a variety of supernova models, including standard as well as hypernova models (for different helium star masses, explosion energies, and explosion geometries) and a simple model for the evolution of the binary and the pollution of the secondary, we show that most of the observed abundance anomalies can be explained for a large range of model parameters (apart from the abundance of Ti). The best models are obtained for He star masses of 10-16M☉, where spherical hypernova models are generally favored over standard supernova ones. Aspherical hypernova models also produce acceptable fits, provided there is extensive lateral mixing. All models require substantial fallback and that the fallback material either reached the orbit of the secondary or was mixed efficiently with material that escaped. The black hole therefore formed in a two-step process, where the initial mass of the collapsed remnant was increased substantially by matter that fell back after the initial collapse. This may help to explain the high observed space velocity of Nova Sco either because of a neutrino-induced kick (if a neutron star was formed first) or by asymmetric mass ejection in an asymmetric supernova explosion.
119247980
Measurement of the track reconstruction efficiency at LHCb
The determination of track reconstruction efficiencies at LHCb using J/psi -> mu(+)mu(-) decays is presented. Efficiencies above 95% are found for the data taking periods in 2010, 2011, and 2012. The ratio of the track reconstruction efficiency of muons in data and simulation is compatible with unity and measured with an uncertainty of 0.8% for data taking in 2010, and at a precision of 0.4% for data taking in 2011 and 2012. For hadrons an additional 1.4% uncertainty due to material interactions is assumed. This result is crucial for accurate cross section and branching fraction measurements in LHCb.
31218324
First results of an aging test of a full scale MWPC prototype for the LHCb muon system
Abstract Aging studies for a multi-wire proportional chamber of the LHCb muon system have been performed using the CERN Gamma Irradiation Facility. The irradiated four-gap chamber corresponds to a full-size prototype with 1500 cm 2 sensitive area and has been operated with an Ar/CO 2 /CF 4 (40:50:10) gas mixture. A linear charge of ∼0.25 C/cm for 100 m anode wire length has been accumulated over a period of 6 months, which corresponds to the charge collected in 5 LHCb years. The observed aging effects do not prohibit the use of these chambers in the LHCb experiment.
41480563
Production and quality control of MWPC for the LHCb muon system at CERN
This work describes the production and quality control of the multi-wire proportional chamber for the LHCb muon detection system. The European Laboratory of Particle Physics (CERN) is in charge of the production of 134 chambers for the inner regions of the five Muon Stations. These chambers have demanding requirements on rate capability (>100 kHz/cm2) and efficiency (>99%) in a short time window (20 ns), on overall response uniformity which has to be better than 30%, and on the aging properties. The technical design of the chambers is briefly presented, and the production line is described together with the quality assurance and quality control programs. This includes fabrication of the panels; wire winding, gluing, and soldering; gap uniformity control; pitch and wire tension measurement; gas leak tests; high-voltage training; and tests under intense radiation. An original method developed for gas gain uniformity measurements is described in detail, and the obtained results are shown