228 research outputs found
To the positive miscut influence on the crystal collimation efficiency
The paper concerns the crystal based collimation suggested to upgrade the
Large Hadron Collider collimation system. The issue of collimation efficiency
dependence on the muscut angle characterizing nonparallelity of the channeling
planes and crystal surface is mainly addressed. It is shown for the first time
that even the preferable positive miscut could severely deteriorate the
channeling collimation efficiency in the crystal collimation UA9 experiment. We
demonstrate that the positive miscut influence can increase the nuclear
reaction rate in the perfectly aligned crystal collimator by a factor of 4.5.
We also discuss the possible miscut influence on the future LHC crystal
collimation system performance as well as suggest simple estimates for the beam
diffusion step, average impact parameter of particle collisions with the
collimator and angular divergence of the colliding particle beam portion.Comment: 14 pages, 9 figure
CRYSTAL Simulation Code and New Coherent Effects in Bent Crystal at the LHC
The LHC crystal-based collimation system is mainly addressed. A CRYSTAL
simulation code for particle tracking in crystals is introduced. Its essence
consists in both adequate and fast sampling of proton trajectories in crystals
which is crucial for both correct description of experiments and quantitative
prediction of new effects. The H8 single-pass experiment at the CERN SPS as
well as 7 TeV proton deflection by a bent crystal at the LHC are simulated. We
predict the existence of dechanneling peaks corresponding to the planar
channeling oscillations as well as describe the possibility of their
observation at high energies, specifically in the LHC crystal-assisted
collimation experiment planned on 2015. An effect of excess over the amorphous
level of ionization losses in the channeling mode was also found for the LHC
energy. In addition, the LHC crystal-based collimation system is simulated as
well as its possible improved layouts with application of a crystal with the
cut and multiple volume reflection in one bent crystal.Comment: The results of this paper were presented on the 6th International
Conference "Charged & Neutral Particles Channeling Phenomena - Channeling
2014" organized by the Italian National Institute for Nuclear Physics (INFN)
and the European Organization for Nuclear Research (CERN) held in Capri
(Capri-Naples, Italy) on October 5-10, 201
Planar channeling and quasichanneling oscillations in a bent crystal
Particles passing through a crystal under planar channeling experience
transverse oscillations in their motion. As channeled particles approach the
atomic planes of a crystal, they are likely to be dechanneled. This effect was
used in ion-beam analysis with MeV energy. We studied this effect in a bent
crystal for positive and negative particles within a wide range of energies in
sight of application of such crystals at accelerators. We found the conditions
for the appearance or not of channeling oscillations. Indeed a new kind of
oscillations, strictly related to the motion of over-barrier particles, i.e.
quasichanneling particles, has been predicted. Such oscillations, named planar
quasichanneling oscillations, possess a different nature than channeling
oscillations. Through computer simulation, we studied this effect and provided
a theoretical interpretation for them. We show that channeling oscillations can
be observed only for positive particles while quasichanneling oscillations can
exist for particles with either sign. The conditions for experimental
observation of channeling and quasichanneling oscillations at existing
accelerators with available crystal has been found and optimized.Comment: 25 pages, 11 figure
simulation code for modeling of coherent effects of radiation generation in oriented crystals
We present the crystalrad simulation code, combining all the features of the crystal simulation code for simulations of charged particles trajectories in a bent crystal and the radcharm++ code for calculation of the radiation spectrum. The crystalrad code is based on Monte Carlo simulations of trajectories in the planar and axial electric field either in a straight, bent, or periodically bent crystal taking into account multiple and single Coulomb scattering on nuclei and electrons, nuclear scattering and ionization energy losses. The trajectories simulated are used for calculation of radiation spectra by the Baier-Katkov method. We compare our simulations with experimental data taken at MAMI (MAinzer MIkrotron) as well as give an example for a possible future study with sub-GeV electrons interacting with Si bent crystals
The miscut angle influence on the future LHC crystal based collimation system
The paper concerns the future LHC crystal based collimation system. The dependence of collimation efficiency on the muscut angle characterizing nonparallelity of the channeling planes and crystal surface is mainly addressed. We demonstrate that even the preferable positive miscut can increase the nuclear reaction rate in the perfectly aligned crystal collimator by a factor of 4.5 in the UA9 experiment. We also discuss the possible miscut influence on the future LHC crystal collimation system suggesting simple estimates for the beam diffusion step, average impact parameter of particle collisions with the collimator and angular divergence of the colliding particle beam portion.Для будущей системы коллимации ускорителя LHC при помощи кристаллов обсуждается зависимость эффективности коллимации от миската угла, характеризующегося непараллельностью кристаллических плоскостей и поверхности кристалла. Показано, что даже предпочтительный положительный мискат может увеличить число ядерных реакций в идеально ориентированном кристаллическом коллиматоре в 4,5 раза в эксперименте UA9. Для исследования возможного влияния миската на будущую систему коллимации БАКа предложены простые оценки диффузионного шага пучка, среднего прицельного параметра падения частицы на коллиматор и угловой расходимости падающего пучка.Для майбутньої системи колімації прискорювача LHC за допомогою кристалів обговорюється залежність ефективності колімації від міскату кута, що характеризується непаралельністю кристалічних площин і поверхні кристала. Показано, що навіть кращий позитивний міскат може збільшити число ядерних реакцій в ідеально орієнтованому кристалічному коліматорі в 4,5 рази в експерименті UA9. Для дослідження можливого впливу міскату на майбутню систему колімації LHC запропоновані прості оцінки дифузійного кроку пучка, середнього прицільного параметра падіння частинки на коліматор і кутової розбіжності падаючого пучка
Relaxation of axially confined 400 GeV/c protons to planar channeling in a bent crystal
An investigation on the mechanism of relaxation
of axially confined 400 GeV/c protons to planar channeling
in a bent crystal was carried out at the extracted line H8 from
CERN Super Proton Synchrotron. The experimental results
were critically compared to computer simulations, showing
a good agreement. We identified a necessary condition for
the exploitation of axial confinement or its relaxation for
particle beam manipulation in high-energy accelerators. We
introduce the idea of using a short bent crystal, aligned with
one of its main axis to the beam direction, as a beam steerer
or a beam splitter with adjustable intensity in the field of particle
accelerators. In particular, in the latter case, a complete
relaxation from axial confinement to planar channeling takes
place, resulting in beam splitting into the two strongest skew
planar channels.An investigation on the mechanism of relaxation of axially confined 400 GeV/c protons to planar channeling in a bent crystal was carried out at the extracted line H8 from CERN Super Proton Synchrotron. The experimental results were critically compared to computer simulations, showing a good agreement. We identified a necessary condition for the exploitation of axial confinement or its relaxation for particle beam manipulation in high-energy accelerators. We introduce the idea of using a short bent crystal, aligned with one of its main axis to the beam direction, as a beam steerer or a beam splitter with adjustable intensity in the field of particle accelerators. In particular, in the latter case, a complete relaxation from axial confinement to planar channeling takes place, resulting in beam splitting into the two strongest skew planar channels
Verification of Photometric Parallaxes with Gaia DR2 Data
Results of comparison of Gaia DR2 parallaxes with data derived from a
combined analysis of 2MASS (Two Micron All-Sky Survey), SDSS (Sloan Digital Sky
Survey), GALEX (Galaxy Evolution Explorer), and UKIDSS (UKIRT Infrared Deep Sky
Survey) surveys in four selected high-latitude sky areas are
presented. It is shown that multicolor photometric data from large modern
surveys can be used for parameterization of stars closer than 4400 pc and
brighter than , including estimation of parallax and
interstellar extinction value. However, the stellar luminosity class should be
properly determined.Comment: 11 pages, 5 figure
Novae Ejecta as Colliding Shells
Following on our initial absorption-line analysis of fifteen novae spectra we
present additional evidence for the existence of two distinct components of
novae ejecta having different origins. As argued in Paper I one component is
the rapidly expanding gas ejected from the outer layers of the white dwarf by
the outburst. The second component is pre-existing outer, more slowly expanding
circumbinary gas that represents ejecta from the secondary star or accretion
disk. We present measurements of the emission-line widths that show them to be
significantly narrower than the broad P Cygni profiles that immediately precede
them. The emission profiles of novae in the nebular phase are distinctly
rectangular, i.e., strongly suggestive of emission from a relatively thin,
roughly spherical shell. We thus interpret novae spectral evolution in terms of
the collision between the two components of ejecta, which converts the early
absorption spectrum to an emission-line spectrum within weeks of the outburst.
The narrow emission widths require the outer circumbinary gas to be much more
massive than the white dwarf ejecta, thereby slowing the latter's expansion
upon collision. The presence of a large reservoir of circumbinary gas at the
time of outburst is suggestive that novae outbursts may sometime be triggered
by collapse of gas onto the white dwarf, as occurs for dwarf novae, rather than
steady mass transfer through the inner Lagrangian point.Comment: 12 pages, 3 figures; Revised manuscript; Accepted for publication in
Astrophysics & Space Scienc
- …