27,518 research outputs found
The ALICE TPC, a large 3-dimensional tracking device with fast readout for ultra-high multiplicity events
The design, construction, and commissioning of the ALICE Time-Projection
Chamber (TPC) is described. It is the main device for pattern recognition,
tracking, and identification of charged particles in the ALICE experiment at
the CERN LHC. The TPC is cylindrical in shape with a volume close to 90 m^3 and
is operated in a 0.5 T solenoidal magnetic field parallel to its axis.
In this paper we describe in detail the design considerations for this
detector for operation in the extreme multiplicity environment of central
Pb--Pb collisions at LHC energy. The implementation of the resulting
requirements into hardware (field cage, read-out chambers, electronics),
infrastructure (gas and cooling system, laser-calibration system), and software
led to many technical innovations which are described along with a presentation
of all the major components of the detector, as currently realized. We also
report on the performance achieved after completion of the first round of
stand-alone calibration runs and demonstrate results close to those specified
in the TPC Technical Design Report.Comment: 55 pages, 82 figure
An optical fiber based interferometer to measure velocity profiles in sheared complex fluids
We describe an optical fiber based interferometer to measure velocity
profiles in sheared complex fluids using Dynamic Light Scattering (DLS). After
a review of the theoretical problem of DLS under shear, a detailed description
of the setup is given. We outline the various experimental difficulties induced
by refraction when using a Couette cell. We also show that homodyne DLS is not
well suited to measure quantitative velocity profiles in narrow-gap Couette
geometries. On the other hand, the heterodyne technique allows us to determine
the velocity field inside the gap of a Couette cell. All the technical features
of the setup, namely its spatial resolution (--m) and its
temporal resolution ( s per point, min per profile) are
discussed, as well as the calibration procedure with a Newtonian fluid. As
briefly shown on oil-in-water emulsions, such a setup permits one to record
both velocity profiles and rheological data simultaneouslyComment: 13 pages, 16 figures, Submitted to Eur. Phys. J. A
CMS Central Hadron Calorimeter
We present a description of the CMS central hadron calorimeter. We describe
the production of the 1996 CMS hadron testbeam module. We show the results of
the quality control tests of the testbeam module. We present some results of
the 1995 CMS hadron testbeam.Comment: 7 pages, 11 Figures, corresponding author: H. Budd, [email protected]
The Fringe Detection Laser Metrology for the GRAVITY Interferometer at the VLTI
Interferometric measurements of optical path length differences of stars over
large baselines can deliver extremely accurate astrometric data. The
interferometer GRAVITY will simultaneously measure two objects in the field of
view of the Very Large Telescope Interferometer (VLTI) of the European Southern
Observatory (ESO) and determine their angular separation to a precision of 10
micro arcseconds in only 5 minutes. To perform the astrometric measurement with
such a high accuracy, the differential path length through the VLTI and the
instrument has to be measured (and tracked since Earth's rotation will
permanently change it) by a laser metrology to an even higher level of accuracy
(corresponding to 1 nm in 3 minutes). Usually, heterodyne differential path
techniques are used for nanometer precision measurements, but with these
methods it is difficult to track the full beam size and to follow the light
path up to the primary mirror of the telescope. Here, we present the
preliminary design of a differential path metrology system, developed within
the GRAVITY project. It measures the instrumental differential path over the
full pupil size and up to the entrance pupil location. The differential phase
is measured by detecting the laser fringe pattern both on the telescopes'
secondary mirrors as well as after reflection at the primary mirror. Based on
our proposed design we evaluate the phase measurement accuracy based on a full
budget of possible statistical and systematic errors. We show that this
metrology design fulfills the high precision requirement of GRAVITY.Comment: Proc. SPIE in pres
A Step-by-step Guide to the Realisation of Advanced Optical Tweezers
Since the pioneering work of Arthur Ashkin, optical tweezers have become an
indispensable tool for contactless manipulation of micro- and nanoparticles.
Nowadays optical tweezers are employed in a myriad of applications
demonstrating the importance of these tools. While the basic principle of
optical tweezers is the use of a strongly focused laser beam to trap and
manipulate particles, ever more complex experimental set-ups are required in
order to perform novel and challenging experiments. With this article, we
provide a detailed step- by-step guide for the construction of advanced optical
manipulation systems. First, we explain how to build a single-beam optical
tweezers on a home-made microscope and how to calibrate it. Improving on this
design, we realize a holographic optical tweezers, which can manipulate
independently multiple particles and generate more sophisticated wavefronts
such as Laguerre-Gaussian beams. Finally, we explain how to implement a speckle
optical tweezers, which permit one to employ random speckle light fields for
deterministic optical manipulation.Comment: 29 pages, 7 figure
Analytical and experimental investigations of low level acceleration measurement techniques
Construction techniques for accelerometer with low level threshold sensitivit
Joint Elastic Side-Scattering Lidar and Raman Lidar Measurements of Aerosol Optical Properties in South East Colorado
We describe an experiment, located in south-east Colorado, USA, that measured
aerosol optical depth profiles using two Lidar techniques. Two independent
detectors measured scattered light from a vertical UV laser beam. One detector,
located at the laser site, measured light via the inelastic Raman
backscattering process. This is a common method used in atmospheric science for
measuring aerosol optical depth profiles. The other detector, located
approximately 40km distant, viewed the laser beam from the side. This detector
featured a 3.5m2 mirror and measured elastically scattered light in a bistatic
Lidar configuration following the method used at the Pierre Auger cosmic ray
observatory. The goal of this experiment was to assess and improve methods to
measure atmospheric clarity, specifically aerosol optical depth profiles, for
cosmic ray UV fluorescence detectors that use the atmosphere as a giant
calorimeter. The experiment collected data from September 2010 to July 2011
under varying conditions of aerosol loading. We describe the instruments and
techniques and compare the aerosol optical depth profiles measured by the Raman
and bistatic Lidar detectors.Comment: 34 pages, 16 figure
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