2,850 research outputs found
Simulation of Beam-Beam Effects and Tevatron Experience
Effects of electromagnetic interactions of colliding bunches in the Tevatron
had a variety of manifestations in beam dynamics presenting vast opportunities
for development of simulation models and tools. In this paper the computer code
for simulation of weak-strong beam-beam effects in hadron colliders is
described. We report the collider operational experience relevant to beam-beam
interactions, explain major effects limiting the collider performance and
compare results of observations and measurements with simulations.Comment: 23 pages, 17 figure
Wavelength Dependent PSFs and their impact on Weak Lensing Measurements
We measure and model the wavelength dependence of the PSF in the Hyper
Suprime-Cam (HSC) Subaru Strategic Program (SSP) survey. We find that PSF
chromaticity is present in that redder stars appear smaller than bluer stars in
the and -bands at the 1-2 per cent level and in the and
-bands at the 0.1-0.2 per cent level. From the color dependence of the PSF,
we fit a model between the monochromatic PSF trace radius, , and wavelength
of the form . We find values of between -0.2
and -0.5, depending on the epoch and filter. This is consistent with the
expectations of a turbulent atmosphere with an outer scale length of m, indicating that the atmosphere is dominating the chromaticity. We
find evidence in the best seeing data that the optical system and detector also
contribute some wavelength dependence. Meyers and Burchat (2015) showed that
must be measured to an accuracy of not to dominate the
systematic error budget of the Large Synoptic Survey Telescope (LSST) weak
lensing (WL) survey. Using simple image simulations, we find that can be
inferred with this accuracy in the and -bands for all positions in the
LSST field of view, assuming a stellar density of 1 star arcmin and that
the optical PSF can be accurately modeled. Therefore, it is possible to correct
for most, if not all, of the bias that the wavelength-dependent PSF will
introduce into an LSST-like WL survey.Comment: 14 pages, 10 figures. Submitted to MNRAS. Comments welcom
Symmetric achromatic low-beta collider interaction region design concept
We present a new symmetry-based concept for an achromatic low-beta collider
interaction region design. A specially-designed symmetric Chromaticity
Compensation Block (CCB) induces an angle spread in the passing beam such that
it cancels the chromatic kick of the final focusing quadrupoles. Two such CCBs
placed symmetrically around an interaction point allow simultaneous
compensation of the 1st-order chromaticities and chromatic beam smear at the IP
without inducing significant 2nd-order aberrations to the particle trajectory.
We first develop an analytic description of this approach and explicitly
formulate 2nd-order aberration compensation conditions at the interaction
point. The concept is next applied to develop an interaction region design for
the ion collider ring of an electron-ion collider. We numerically evaluate
performance of the design in terms of momentum acceptance and dynamic aperture.
The advantages of the new concept are illustrated by comparing it to the
conventional distributed-sextupole chromaticity compensation scheme.Comment: 12 pages, 17 figures, to be submitted to Phys. Rev. ST Accel. Beam
Analytical considerations for linear and nonlinear optimization of the TME cells. Application to the CLIC pre-damping rings
The theoretical minimum emittance cells are the optimal configurations for
achieving the absolute minimum emittance, if specific optics constraints are
satisfied at the middle of the cell's dipole. Linear lattice design options
based on an analytical approach for the theoretical minimum emittance cells are
presented in this paper. In particular the parametrization of the quadrupole
strengths and optics functions with respect to the emittance and drift lengths
is derived. A multi-parametric space can be then created with all the cell
parameters, from which one can chose any of them to be optimized. An
application of this approach are finally presented for the linear and
non-linear optimization of the CLIC Pre-damping rings.Comment: Submitted for publication in Physical Review Special Topics -
Accelerators and Beam
Digital Color Imaging
This paper surveys current technology and research in the area of digital
color imaging. In order to establish the background and lay down terminology,
fundamental concepts of color perception and measurement are first presented
us-ing vector-space notation and terminology. Present-day color recording and
reproduction systems are reviewed along with the common mathematical models
used for representing these devices. Algorithms for processing color images for
display and communication are surveyed, and a forecast of research trends is
attempted. An extensive bibliography is provided
White Organic Light-Emitting Diodes with fine chromaticity tuning via ultrathin layer position shifting
Non-doped white organic light-emitting diodes using an ultrathin
yellow-emitting layer of rubrene (5,6,11,12-tetraphenylnaphtacene) inserted on
either side of the interface between a hole-transporting NPB
(4,4'-bis[N-(1-naphtyl)-N-phenylamino]biphenyl) layer and a blue-emitting DPVBi
(4,4'-bis(2,2'-diphenylvinyl)-1,1'-biphenyl) layer are described. Both the
thickness and the position of the rubrene layer allow fine chromaticity tuning
from deep-blue to pure-yellow via bright-white with CIE coordinates (x= 0.33,
y= 0.32), a external quantum efficiency of 1.9%, and a color rendering index of
70. Such a structure also provides an accurate sensing tool to measure the
exciton diffusion length in both DPVBi and NPB (8.7 and 4.9 nm respectively)
White organic light-emitting diodes with an ultra-thin premixed emitting layer
We described an approach to achieve fine color control of fluorescent White
Organic Light-Emitting Diodes (OLED), based on an Ultra-thin Premixed emitting
Layer (UPL). The UPL consists of a mixture of two dyes (red-emitting
4-di(4'-tert-butylbiphenyl-4-yl)amino-4'-dicyanovinylbenzene or fvin and
green-emitting 4-di(4'-tert-butylbiphenyl-4-yl)aminobenzaldehyde or fcho)
premixed in a single evaporation cell: since these two molecules have
comparable structures and similar melting temperatures, a blend can be
evaporated, giving rise to thin films of identical and reproducible composition
compared to those of the pre-mixture. The principle of fine color tuning is
demonstrated by evaporating a 1-nm-thick layer of this blend within the
hole-transport layer (4,4'-bis[N-(1-naphtyl)-N-phenylamino]biphenyl
(\alpha-NPB)) of a standard fluorescent OLED structure. Upon playing on the
position of the UPL inside the hole-transport layer, as well as on the premix
composition, two independent parameters are available to finely control the
emitted color. Combined with blue emission from the heterojunction, white light
with Commission Internationale de l'Eclairage 1931 color coordinates (0.34,
0.34) was obtained, with excellent color stability with the injected current.
The spectrum reveals that the fcho material does not emit light due to
efficient energy transfer to the red-emitting fvin compound but plays the role
of a host matrix for fvin, allowing for a very precise adjustment of the red
dopant amount in the device
Damping rate limitations for transverse dampers in large hadron colliders
The paper focuses on two issues important for design and operation of
bunch-by-bunch transverse damper in a very large hadron collider, where fast
damping is required to suppress beam instabilities and noise induced emittance
growth. The first issue is associated with kick variation along a bunch which
affects the damping of head-tail modes. The second issue is associated with
affect of damper noise on the instability threshold
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