6,700 research outputs found
Theory of Dispersed Fixed-Delay Interferometry for Radial Velocity Exoplanet Searches
The dispersed fixed-delay interferometer (DFDI) represents a new instrument
concept for high-precision radial velocity (RV) surveys for extrasolar planets.
A combination of Michelson interferometer and medium-resolution spectrograph,
it has the potential for performing multi-object surveys, where most previous
RV techniques have been limited to observing only one target at a time. Because
of the large sample of extrasolar planets needed to better understand planetary
formation, evolution, and prevalence, this new technique represents a logical
next step in instrumentation for RV extrasolar planet searches, and has been
proven with the single-object Exoplanet Tracker (ET) at Kitt Peak National
Observatory, and the multi-object W. M. Keck/MARVELS Exoplanet Tracker at
Apache Point Observatory. The development of the ET instruments has
necessitated fleshing out a detailed understanding of the physical principles
of the DFDI technique. Here we summarize the fundamental theoretical material
needed to understand the technique and provide an overview of the physics
underlying the instrument's working. We also derive some useful analytical
formulae that can be used to estimate the level of various sources of error
generic to the technique, such as photon shot noise when using a fiducial
reference spectrum, contamination by secondary spectra (e.g., crowded sources,
spectroscopic binaries, or moonlight contamination), residual interferometer
comb, and reference cross-talk error. Following this, we show that the use of a
traditional gas absorption fiducial reference with a DFDI can incur significant
systematic errors that must be taken into account at the precision levels
required to detect extrasolar planets.Comment: 58 pages, 11 figures, 1 table, 3 appendices. Accepted for publication
in ApJS. Minor typographical corrections; update to acknowledgment
Front-end Multiplexing - applied to SQUID multiplexing : Athena X-IFU and QUBIC experiments
As we have seen for digital camera market and a sensor resolution increasing
to "megapixels", all the scientific and high-tech imagers (whatever the wave
length - from radio to X-ray range) tends also to always increases the pixels
number. So the constraints on front-end signals transmission increase too. An
almost unavoidable solution to simplify integration of large arrays of pixels
is front-end multiplexing. Moreover, "simple" and "efficient" techniques allow
integration of read-out multiplexers in the focal plane itself. For instance,
CCD (Charge Coupled Device) technology has boost number of pixels in digital
camera. Indeed, this is exactly a planar technology which integrates both the
sensors and a front-end multiplexed readout. In this context, front-end
multiplexing techniques will be discussed for a better understanding of their
advantages and their limits. Finally, the cases of astronomical instruments in
the millimeter and in the X-ray ranges using SQUID (Superconducting QUantum
Interference Device) will be described
Basics of RF electronics
RF electronics deals with the generation, acquisition and manipulation of
high-frequency signals. In particle accelerators signals of this kind are
abundant, especially in the RF and beam diagnostics systems. In modern machines
the complexity of the electronics assemblies dedicated to RF manipulation, beam
diagnostics, and feedbacks is continuously increasing, following the demands
for improvement of accelerator performance. However, these systems, and in
particular their front-ends and back-ends, still rely on well-established basic
hardware components and techniques, while down-converted and acquired signals
are digitally processed exploiting the rapidly growing computational capability
offered by the available technology. This lecture reviews the operational
principles of the basic building blocks used for the treatment of
high-frequency signals. Devices such as mixers, phase and amplitude detectors,
modulators, filters, switches, directional couplers, oscillators, amplifiers,
attenuators, and others are described in terms of equivalent circuits,
scattering matrices, transfer functions; typical performance of commercially
available models is presented. Owing to the breadth of the subject, this review
is necessarily synthetic and non-exhaustive. Readers interested in the
architecture of complete systems making use of the described components and
devoted to generation and manipulation of the signals driving RF power plants
and cavities may refer to the CAS lectures on Low-Level RF.Comment: 36 pages, contribution to the CAS - CERN Accelerator School:
Specialised Course on RF for Accelerators; 8 - 17 Jun 2010, Ebeltoft, Denmar
Probing supernova shock waves and neutrino flavor transitions in next-generation water-Cherenkov detectors
Several current projects aim at building a large water-Cherenkov detector,
with a fiducial volume about 20 times larger than in the current
Super-Kamiokande experiment. These projects include the Underground nucleon
decay and Neutrino Observatory (UNO) in the Henderson Mine (Colorado), the
Hyper-Kamiokande (HK) detector in the Tochibora Mine (Japan), and the MEgaton
class PHYSics (MEMPHYS) detector in the Frejus site (Europe). We study the
physics potential of a reference next-generation detector (0.4 Mton of fiducial
mass) in providing information on supernova neutrino flavor transitions with
unprecedented statistics. After discussing the ingredients of our calculations,
we compute neutrino event rates from inverse beta decay (), elastic scattering on electrons, and scattering on oxygen, with emphasis on
their time spectra, which may encode combined information on neutrino
oscillation parameters and on supernova forward (and possibly reverse) shock
waves. In particular, we show that an appropriate ratio of low-to-high energy
events can faithfully monitor the time evolution of the neutrino crossing
probability along the shock-wave profile. We also discuss some background
issues related to the detection of supernova relic neutrinos, with and without
the addition of gadolinium.Comment: Revised version (27 pages, 13 eps figures), to appear in JCAP.
Includes revised numerical estimates and figures. In particular: calculations
of inverse beta decay event rates improved by using the differential cross
section by Vissani and Strumia (astro-ph/0302055); supernova relic neutrino
flux calculations updated by using recent GALEX Mission data
(astro-ph/0411424) on the star formation rate (SFR). References added.
Conclusions unchange
Comparison of direct and heterodyne detection optical intersatellite communication links
The performance of direct and heterodyne detection optical intersatellite communication links are evaluated and compared. It is shown that the performance of optical links is very sensitive to the pointing and tracking errors at the transmitter and receiver. In the presence of random pointing and tracking errors, optimal antenna gains exist that will minimize the required transmitter power. In addition to limiting the antenna gains, random pointing and tracking errors also impose a power penalty in the link budget. This power penalty is between 1.6 to 3 dB for a direct detection QPPM link, and 3 to 5 dB for a heterodyne QFSK system. For the heterodyne systems, the carrier phase noise presents another major factor of performance degradation that must be considered. In contrast, the loss due to synchronization error is small. The link budgets for direct and heterodyne detection systems are evaluated. It is shown that, for systems with large pointing and tracking errors, the link budget is dominated by the spatial tracking error, and the direct detection system shows a superior performance because it is less sensitive to the spatial tracking error. On the other hand, for systems with small pointing and tracking jitters, the antenna gains are in general limited by the launch cost, and suboptimal antenna gains are often used in practice. In which case, the heterodyne system has a slightly higher power margin because of higher receiver sensitivity
Infrastructure for Detector Research and Development towards the International Linear Collider
The EUDET-project was launched to create an infrastructure for developing and
testing new and advanced detector technologies to be used at a future linear
collider. The aim was to make possible experimentation and analysis of data for
institutes, which otherwise could not be realized due to lack of resources. The
infrastructure comprised an analysis and software network, and instrumentation
infrastructures for tracking detectors as well as for calorimetry.Comment: 54 pages, 48 picture
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