20,939 research outputs found
Synchro-Betatron Stop-Bands due to a Single Crab Cavity
We analyze the stop-band due to crab cavities for horizontal tunes that are
either close to integers or close to half integers. The latter case is relevant
for today's electron/positron colliders. We compare this stop-band to that
created by dispersion in an accelerating cavity and show that a single typical
crab cavity creates larger stop-bands than a typical dispersion at an
accelerating cavity.
We furthermore analyze whether it is beneficial to place the crab cavity at a
position where the dispersion and its slope vanish. We find that this choice is
worth while if the horizontal tune is close to a half integer, but not if it is
close to an integer. Furthermore we find that stop-bands can be avoided when
the horizontal tune is located at a favorable side of the integer or the half
integer.
While we are here concerned with the installation of a single crab cavity in
a storage ring, we show that the stop-bands can be weakened, although not
eliminated, significantly when two crab cavities per ring are chosen suitably.Comment: 7 pages, 9 figure
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Summary of the impedance working group
The impedance working group concentrated on the LHC design during the workshop. They look at the impedance contributions of liner, beam position monitors, shielded bellows, experimental chambers, superconducting cavities, recombination chambers, space charge, kickers, and the resistive wall. The group concluded that the impedance budgeting and the conceptual designs of the vacuum chamber components looked basically sound. It also noted, not surprisingly, that a large amount of studies are to be carried out further, and it ventured to give a partial list of these studies
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Studying resist stochastics with the multivariate poisson propagation model
Progress in the ultimate performance of extreme ultraviolet resist has arguably decelerated in recent years suggesting an approach to stochastic limits both in photon counts and material parameters. Here we report on the performance of a variety of leading extreme ultraviolet resist both with and without chemical amplification. The measured performance is compared to stochastic modeling results using the Multivariate Poisson Propagation Model. The results show that the best materials are indeed nearing modeled performance limits
Electron Refrigeration in the Tunneling Approach
The qualities of electron refrigeration by means of tunnel junctions between
superconducting and normal--metal electrodes are studied theoretically. A
suitable approximation of the basic expression for the heat current across
those tunnel junctions allows the investigation of several features of the
device such as its optimal bias voltage, its maximal heat current, its optimal
working point, and the maximally gained temperature reduction. Fortunately, the
obtained results can be compared with those of a recent experiment.Comment: 4 pages, 4 Postscript figures, uses eps
Joint Reconstruction of Absorbed Optical Energy Density and Sound Speed Distribution in Photoacoustic Computed Tomography: A numerical Investigation
Photoacoustic computed tomography (PACT) is a rapidly emerging bioimaging
modality that seeks to reconstruct an estimate of the absorbed optical energy
density within an object. Conventional PACT image reconstruction methods assume
a constant speed-of-sound (SOS), which can result in image artifacts when
acoustic aberrations are significant. It has been demonstrated that
incorporating knowledge of an object's SOS distribution into a PACT image
reconstruction method can improve image quality. However, in many cases, the
SOS distribution cannot be accurately and/or conveniently estimated prior to
the PACT experiment. Because variations in the SOS distribution induce
aberrations in the measured photoacoustic wavefields, certain information
regarding an object's SOS distribution is encoded in the PACT measurement data.
Based on this observation, a joint reconstruction (JR) problem has been
proposed in which the SOS distribution is concurrently estimated along with the
sought-after absorbed optical energy density from the photoacoustic measurement
data. A broad understanding of the extent to which the JR problem can be
accurately and reliably solved has not been reported. In this work, a series of
numerical experiments is described that elucidate some important properties of
the JR problem that pertain to its practical feasibility. To accomplish this,
an optimization-based formulation of the JR problem is developed that yields a
non-linear iterative algorithm that alternatingly updates the two image
estimates. Heuristic analytic insights into the reconstruction problem are also
provided. These results confirm the ill-conditioned nature of the joint
reconstruction problem that will present significant challenges for practical
applications.Comment: 13 pages, submitted to IEEE Transactions on Computational Imagin
A tracking algorithm for the stable spin polarization field in storage rings using stroboscopic averaging
Polarized protons have never been accelerated to more than about GeV. To
achieve polarized proton beams in RHIC (250GeV), HERA (820GeV), and the
TEVATRON (900GeV), ideas and techniques new to accelerator physics are needed.
In this publication we will stress an important aspect of very high energy
polarized proton beams, namely the fact that the equilibrium polarization
direction can vary substantially across the beam in the interaction region of a
high energy experiment when no countermeasure is taken. Such a divergence of
the polarization direction would not only diminish the average polarization
available to the particle physics experiment, but it would also make the
polarization involved in each collision analyzed in a detector strongly
dependent on the phase space position of the interacting particle. In order to
analyze and compensate this effect, methods for computing the equilibrium
polarization direction are needed. In this paper we introduce the method of
stroboscopic averaging, which computes this direction in a very efficient way.
Since only tracking data is needed, our method can be implemented easily in
existing spin tracking programs. Several examples demonstrate the importance of
the spin divergence and the applicability of stroboscopic averaging.Comment: 39 page
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