1,720,984 research outputs found
Simulations of RF beam manipulations including intensity effects for CERN PSB and SPS upgrades
Get PDFDuring Long Shutdown 2 (LS2, 2019-2021) all the injectors of the CERN LHC will undergo several upgrades to fulfill the requests of the LHC Injectors Upgrade (LIU) Project. Among them, an increase in luminosity of the LHC beam by a factor of ten and two respectively for proton and ion beams is expected. The upgrades of the CERN PSB, the first synchrotron in the LHC proton injection chain, will be significant. The injection and extraction beam energies will be increased respectively from 50 MeV to 160 MeV kinetic energy (via the new Linac4) and from 1.4 GeV to 2 GeV (using new magnet power supplies). The required beam intensities will be a factor of two higher for High-Luminosity LHC (HL-LHC) beams, and the currently used narrow-band ferrite RF systems will be replaced by broad-band Finemet® cavities. For ion beams instead, a fundamental upgrade will concern the CERN SPS, the LHC injector, where the Low Lever RF functionalities will be considerably enhanced to allow the interleaving of two batches in longitudinal phase space through momentum slip-stacking, aiming at halving the bunch spacing.
In order to predict future longitudinal beam stability and optimize complex RF manipulations both for PSB and SPS, longitudinal macro-particle simulations
have been performed. Concerning the PSB, an accurate impedance model and a careful estimation of the space charge effects were included in simulations. Beam and cavity-based feedbacks were also taken into account. Controlled longitudinal emittance blow-up, currently obtained through phase modulation with a dedicated higher harmonic RF system, was achieved in measurements and simulations for
the first time injecting RF phase noise in the main harmonic cavity, showing some advantages in using this new method. As for the SPS, the slip-stacking dynamics with collective effects has been studied in details aiming at optimizing the numerous parameters present and satisfying the stringent constraints on losses and bunch length at extraction. Beam quality issues were analyzed together with possible remedies. All simulations have been performed with the macro-particle longitudinal beam dynamics CERN BLonD code, after particular efforts have been spent to implement several algorithms for non ultra-relativistic energy machines (like the PSB) and for slip-stacking dynamics in order to easily optimize the large parameter space available. Benchmarks between BLonD, other codes and analytical formulas have been performed to study different approaches for induced voltage calculation and give some guidelines on the pros and cons of each of them
Longitudinal injection schemes for the CERN PS Booster at 160 MeV including space charge effects
No full textImpedance-Induced Beam Instabilities and Damping Mechanisms in Circular Machines – Longitudinal - Simulations
No full textPreparations for upgrading the RF systems of the PS Booster
No full textThe accelerators of the LHC injector chain need to be upgraded to provide the HL-LHC beams. The PS Booster, the first synchrotron in the LHC injection chain, uses three different RF systems (first, second and up to tenth harmonic) in each of its four rings. As part of the LHC Injector Upgrade the current ferrite RF systems will be replaced with broadband Finemet cavities, increasing the flexibility of the RF system. A Finemet test cavity has been installed in Ring 4 to investigate its effect on machine performance, especially beam stability, during extensive experimental studies. Due to large space charge impedance Landau damping is lost through most of the cycle in single harmonic operation, but is recovered when using the second harmonic and controlled longitudinal emittance blow-up. This paper compares beam parameters during acceleration with and without the Finemet test cavity. Comparisons were made using beam measurements and simulations with the BLonD code based on a full PS Booster impedance model. This work, together with simulations of future operation, have provided input for the decision to adopt a fully Finemet RF system
Benchmarking the Beam Longitudinal Dynamics Code BLOND
No full textThe relatively recent Beam Longitudinal Dynamics code BLonD has already been applied to a wide range of studies for all present CERN synchrotrons. Its application area ranges from studies of RF manipulations, over single and multi-bunch interactions with impedance, to the action of feedback loops and RF noise. In this paper, we present benchmarks and comparisons with measurements, theory, or other codes, which have increased greatly the trust in the code. Tests related to bunch-to-bucket transfer, feedback loops, diffusion due to noise injection, as well as collective effects, are presented
CERN PS Booster longitudinal dynamics simulations for the post-LS2 scenario
No full textThe CERN PS Booster is the first synchrotron in the LHC proton injection chain, it currently accelerates particles from 50 MeV to 1.4 GeV kinetic energy. Several upgrades foreseen by the LHC Injectors Upgrade Program will allow the beam to be accelerated from 160 MeV to 2 GeV after Long Shutdown 2 in 2021. The present RF systems will be replaced by a new one, based on Finemet technology. These and other improvements will help to increase the LHC luminosity by a factor of ten. In order to study beam stability in the longitudinal plane simulations have been performed with the CERN BLonD code, using an accurate longitudinal impedance model and a reliable estimation of the longitudinal space charge. Particular attention has been dedicated to the three main features that currently let the beam go stably through the ramp: Double RF operation in bunch-lengthening mode to reduce the transverse space charge tune spread, exploitation of feedback loops to damp dipole oscillations, and controlled longitudinal emittance blow-up. RF phase noise injection has been considered to study if it could complement or substitute the currently used method based on sinusoidal phase modulation
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
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