11 research outputs found
BEAM SCRAPING FOR LHC INJECTION: HIGH LEVEL APPLICATION DEVELOPMENT
The Large Hadron Collider (LHC) at CERN (European Organization for Nuclear Research) will be the world's most powerful accelerator when it is commissioned during 2008. To operate the LHC, injection of very high intensity beams from the Super Proton Synchrotron (SPS) pre-accelerator is required. With intensities of more than 3 _ 1013 p=cycle, it is essential that there is virtually no beam halo present. Such particles can hit the LHC beam pipe, and may cause magnet quenches due to heating. Fast scrapers have been installed in the SPS to measure and remove any halo before the beam is extracted towards the LHC. Fast scrapers have been chosen because there is too little time available for beam cleaning with large collimators. The scraper hardware has been in place in the SPS ring for several years. A low level computer for controlling the scrapers is also in place. A high level control application was, however, not written at the time. The development of the missing high level control application is the subject of this work. The functional requirements for the application have been established in a report by G. Arduini and H. Burkhardt [2]. The application had to be written in Java to be compatible with the control system in the Cern Control Centre (CCC). Java is chosen due to portability between operating systems and due to the large number of freely available libraries. A working application for high level control has been devel oped and released into the software repository for the CCC computers. The application has been tested and used for two machine studies. Other users interested in using the scrapers for machine studies and commissioning have also tested the application. These tests indicate that the application works as expected, and can be used by operators in the future. Also, they have provided valuable feedback for further improvements of the application
Substrate influence on the plasmonic response of clusters of spherical nanoparticles
The plasmonic response of nanoparticles is exploited in many subfields of
science and engineering to enhance optical signals associated with probes of
nanoscale and subnanoscale entities. We develop a numerical algorithm based on
previous theoretical work that addresses the influence of a substrate on the
plasmonic response of collections of nanoparticles of spherical shape. Our
method is a real space approach within the quasi-static limit that can be
applied to a wide range of structures. We illustrate the role of the substrate
through numerical calculations that explore single nanospheres and nanosphere
dimers fabricated from either a Drude model metal or from silver on dielectric
substrates, and from dielectric spheres on silver substrates.Comment: 12 pages, 13 figure
Beam Scraping to detect and remove Halo in LHC Injection
Fast scrapers are installed in the SPS to detect and remove beam halo before extraction of beams to the LHC, to minimize the probability for quenching of superconducting magnets in the LHC. We shortly describe the current system and then focus on our recent work, which aims at providing a system which can be used as operational tool for standard LHC injection. A new control application was written and tested with the beam. We describe the current status and results and compare these with detailed simulations
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Satellite peaks in the scattering of light from the two-dimensional randomly rough surface of a dielectric film on a planar metal surface.
A nonperturbative, purely numerical, solution of the reduced Rayleigh equation for the scattering of p- and s-polarized light from a dielectric film with a two-dimensional randomly rough surface deposited on a planar metallic substrate, has been carried out. It is found that satellite peaks are present in the angular dependence of the elements of the mean differential reflection coefficient in addition to an enhanced backscattering peak. This result resolves a conflict between the results of earlier approximate theoretical studies of scattering from this system
Numerical studies of the transmission of light through a two-dimensional randomly rough interface
The transmission of polarized light through a two-dimensional randomly rough
interface between two dielectric media has been much less studied, by any
approach, than the reflection of light from such an interface. We have derived
a reduced Rayleigh equation for the transmission amplitudes when p- or
s-polarized light is incident on this type of interface, and have obtained
rigorous, purely numerical, nonperturbative solutions of it. The solutions are
used to calculate the transmissivity and transmittance of the interface, the
mean differential transmission coefficient, and the full angular distribution
of the intensity of the transmitted light. These results are obtained for both
the case where the medium of incidence is the optically less dense medium and
in the case where it is the optically more dense medium. Optical analogues of
Yoneda peaks observed in the scattering of x-rays from metal surfaces are
present in the results obtained in the former case. For p-polarized incident
light we observe Brewster scattering angles, angles at which the diffuse
transmitted intensity is zero in a single-scattering approximation, which
depend on the angle of incidence in contrast to the Brewster angle for
flat-surface reflection.Comment: 23 pages, 15 figure
Near-Field Plasmonics of an Individual Dielectric Nanoparticle above a Metallic Substrate
In this work, we simulate and discuss the local electric-field enhancement in a system of a dielectric nanoparticle placed very near to a metallic substrate. We use finite-element numerical simulations in order to understand the field-enhancement mechanism in this dielectric NP-on-mirror system. Under appropriate excitation conditions, the gap between the particle and the substrate becomes a âhot-spotâ, i.e. a region of intense electromagnetic field. In this work, we also show how the optical properties of the dielectric NP placed on a metallic substrate affect the plasmonic field enhancement in the nano-gap and characterize the confinement in the gap. Our study helps to understand and design systems with dielectric NPs on metallic substrates which can be equally as effective for SERS, fluorescence and non-linear phenomena as conventional all-metal plasmonic structures.<br/