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

An algebraic-geometric construction of ind-varieties of generalized flags

We define the class of admissible linear embeddings of flag varieties. The definition is given in the general language of algebraic geometry. We then prove that an admissible linear embedding of flag varieties has a certain explicit form in terms of linear algebra. This result enables us to show that any direct limit of admissible embeddings of flag varieties is isomorphic to an ind-variety of generalized flags as defined in [DP]. These latter ind-varieties have been introduced in terms of the ind-group SL(\infty) (respectively, O(\infty) or Sp(\infty) for isotropic generalized flags), and the current paper constructs them in purely algebraic-geometric term

Collective oscillations in spatially modulated exciton-polariton condensate arrays

We study collective dynamics of interacting centers of exciton-polariton condensation in presence of spatial inhomogeneity, as modeled by diatomic active oscillator lattices. The mode formalism is developed and employed to derive existence and stability criteria of plane wave solutions. It is demonstrated that $k_0=0$ wave number mode with the binary elementary cell on a diatomic lattice possesses superior existence and stability properties. Decreasing net on-site losses (balance of dissipation and pumping) or conservative nonlinearity favors multistability of modes, while increasing frequency mismatch between adjacent oscillators detriments it. On the other hand, spatial inhomogeneity may recover stability of modes at high nonlinearities. Entering the region where all single-mode solutions are unstable we discover subsequent transitions between localized quasiperiodic, chaotic and global chaotic dynamics in the mode space, as nonlinearity increases. Importantly, the last transition evokes the loss of synchronization. These effects may determine lasing dynamics of interacting exciton-polariton condensation centers.Comment: 9 pages, 3 figure

First CRDS-measurements of water vapour continuum in the 940nm absorption band

Measurements of near-infrared water vapour continuum using continuous wave cavity ring down spectroscopy (cw- CRDS) have been performed at around 10611.6 and 10685:2 cm1. The continuum absorption coefficients for N2- broadening have been determined for two temperatures and wavenumbers. These results represent the first near-IR continuum laboratory data determined within the complex spectral environment in the 940nm water vapour band and are in reasonable agreement with simulations using the semiempirical CKD formulation

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