420 research outputs found
Strong unitary and overlap uncertainty relations: theory and experiment
We derive and experimentally investigate a strong uncertainty relation valid
for any unitary operators, which implies the standard uncertainty relation
as a special case, and which can be written in terms of geometric phases. It is
saturated by every pure state of any -dimensional quantum system, generates
a tight overlap uncertainty relation for the transition probabilities of any
pure states, and gives an upper bound for the out-of-time-order
correlation function. We test these uncertainty relations experimentally for
photonic polarisation qubits, including the minimum uncertainty states of the
overlap uncertainty relation, via interferometric measurements of generalised
geometric phases.Comment: 5 pages of main text, 5 pages of Supplemental Material.
Clarifications added in this updated versio
Maximizing precision in saturation-limited absorption measurements
Quantum fluctuations in the intensity of an optical probe is noise which
limits measurement precision in absorption spectroscopy. Increased probe power
can offer greater precision, however, this strategy is often constrained by
sample saturation. Here, we analyse measurement precision for a generalised
absorption model in which we account for saturation and explore its effect on
both classical and quantum probe performance. We present a classical
probe-sample optimisation strategy to maximise precision and find that optimal
probe powers always fall within the saturation regime. We apply our
optimisation strategy to two examples, high-precision Doppler broadened
thermometry and an absorption spectroscopy measurement of Chlorophyll A. We
derive a limit on the maximum precision gained from using a non-classical probe
and find a strategy capable of saturating this bound. We evaluate
amplitude-squeezed light as a viable experimental probe state and find it
capable of providing precision that reaches to within > 85% of the ultimate
quantum limit with currently available technology.Comment: 12 pages and 5 figure
Multi-turn losses and cleaning
In the LHC all multi-turn losses should occur at the collimators in the cleaning insertions. The cleaning inefficiency
(leakage rate) is the figure of merit to describe the performance. In combination with the quench limit of the superconducting magnets and the instantaneous life time of
the beam this defines the cleaning dependent beam intensity limit of the LHC. In addition, limits can arise from
radiation-induced effects, like radiation damage and radation to electronics. In this paper the used collimator settings, the required setup time, the reliability of collimation
(all multi-turn losses at collimators), and the achieved proton/ion cleaning inefficiency are discussed. Observed and
expected losses are compared. The performance evolution
during the months of operation is reviewed. In addition,
the peak losses during high intensity runs, losses caused
by instabilities, and the resulting beam life times are discussed. Taking the observations into account the intensity
reach with collimation at 3.5 and 4 TeV is reviewed.peer-reviewe
First ion collimation commissioning results at the LHC
First commissioning of the LHC lead ion beams to 1.38 A TeV beam energy was successfully achieved in November 2010. Ion collimation has been predicted to be less efficient than for protons at the LHC, because of the complexity of the physical processes involved: nuclear fragmentation and electromagnetic dissociation in the primary collimators creating fragments with a wide range of Z/A ratios, that are not intercepted by the secondary collimators but lost in the dispersion suppressor sections of the ring. In this article we present first comparisons of measured loss maps with theoretical predictions from simulation runs with the ICOSIM code. An extrapolation to define the ultimate intensity limit for Pb beams is attempted. The scope of possible improvements in collimation efficiency coming from the installation of new collimators in the cold dispersion suppressors and combined betatron and momentum cleaning is also explored.Ministerio de Ciencia e Innovacion - Gobierno de Espana,Ayuntamiento de San Sebastian,Gobierno Vasco,Diputacion Foral de Gipuzkoa,San Sebastian Turismo - Convention Bureaupeer-reviewe
End-of-fill study on collimator tight settings
In 2010 and 2011 the collimation system has been operated with relaxed settings, i.e. with retractions between
different collimator families larger than the nominal settings that provide optimum cleaning. This configuration ensured a sufficient cleaning performance at 3.5 TeV while allowing larger tolerances on orbit control.
Tighter collimator settings were proposed to push the cleaning performance and to allow larger orbit margins
between TCDQ dump protection and tertiary collimators. With the same margins as with the relaxed settings, the β∗ could be reduced. After having verified with beam that the cleaning is improved as expected,
the feasibility of tighter collimator settings must be addressed with high stored intensity. For this purpose, an
end-of-fill study was proposed after a standard physics fill with 1380 bunches nominal bunches at 3.5 TeV, for
a total stored energy of 95 MJ. During this test, primary and secondary collimators were moved to tight settings after about 8 hours of stable physics conditions in all experiments. This note summarises the operational
procedure followed and the results of beam measurements during this study.peer-reviewe
Collimation dependent beam lifetime and loss rates in the LHC
The four primary collimators in each LHC beam define the smallest aperture. Particles with high betatron amplitudes or momentum offsets will therefore hit first a primary collimator. The instantaneous particle loss rate at primary collimators measured by precise beam loss monitors (BLM) is an important measure for the global lifetime of the beams and a major ingredient to identify collimation induced performance limitations in the LHC. These loss rates have been measured during a number of LHC fills, featuring both "good" fills with high luminosity and "bad" fills with beam instabilities. The beam lifetime at the collimators was then calculated from these data for different cases. The results are presented and interpreted within this paper.Ministerio de Ciencia e Innovacion - Gobierno de Espana,Ayuntamiento de San Sebastian,Gobierno Vasco,Diputacion Foral de Gipuzkoa,San Sebastian Turismo - Convention Bureau.peer-reviewe
Halo scrapings with collimators in the LHC
Understanding the population and the shape of the beam halo is important to predict possible intensity limitations due to collimation at 7 TeV. Therefore the population of the beam halo has been measured in horizontal, vertical and skew plane, using the primary collimators of the LHC collimation system. In addition these measurements were used to calibrate the beam loss monitor signals to a particle loss rate at the primary collimators. Within this paper the halo scraping method, the measured halo distribution and the calibration factors are presented and discussed.Ministerio de Ciencia e Innovacion - Gobierno de Espana,Ayuntamiento de San Sebastian,Gobierno Vasco,Diputacion Foral de Gipuzkoa,San Sebastian Turismo - Convention Bureau.peer-reviewe
Testing Beam-Induced Quench Levels of LHC Superconducting Magnets
In the years 2009-2013 the Large Hadron Collider (LHC) has been operated with
the top beam energies of 3.5 TeV and 4 TeV per proton (from 2012) instead of
the nominal 7 TeV. The currents in the superconducting magnets were reduced
accordingly. To date only seventeen beam-induced quenches have occurred; eight
of them during specially designed quench tests, the others during injection.
There has not been a single beam- induced quench during normal collider
operation with stored beam. The conditions, however, are expected to become
much more challenging after the long LHC shutdown. The magnets will be
operating at near nominal currents, and in the presence of high energy and high
intensity beams with a stored energy of up to 362 MJ per beam. In this paper we
summarize our efforts to understand the quench levels of LHC superconducting
magnets. We describe beam-loss events and dedicated experiments with beam, as
well as the simulation methods used to reproduce the observable signals. The
simulated energy deposition in the coils is compared to the quench levels
predicted by electro-thermal models, thus allowing to validate and improve the
models which are used to set beam-dump thresholds on beam-loss monitors for Run
2.Comment: 19 page
The First 1 1/2 Years of TOTEM Roman Pot Operation at LHC
Since the LHC running season 2010, the TOTEM Roman Pots (RPs) are fully
operational and serve for collecting elastic and diffractive proton-proton
scattering data. Like for other moveable devices approaching the high intensity
LHC beams, a reliable and precise control of the RP position is critical to
machine protection. After a review of the RP movement control and position
interlock system, the crucial task of alignment will be discussed.Comment: 3 pages, 6 figures; 2nd International Particle Accelerator Conference
(IPAC 2011), San Sebastian, Spain; contribution MOPO01
Structure and function of the Rad9-binding region of the DNA-damage checkpoint adaptor TopBP1
TopBP1 is a scaffold protein that coordinates activation of the DNA-damage-checkpoint response by coupling binding of the 9-1-1 checkpoint clamp at sites of ssDNA, to activation of the ATR-ATRIP checkpoint kinase complex. We have now determined the crystal structure of the N-terminal region of human TopBP1, revealing an unexpected triple-BRCT domain structure. The arrangement of the BRCT domains differs significantly from previously described tandem BRCT domain structures, and presents two distinct sites for binding phosphopeptides in the second and third BRCT domains. We show that the site in the second but not third BRCT domain in the N-terminus of TopBP1, provides specific interaction with a phosphorylated motif at pSer387 in Rad9, which can be generated by CK2
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