122 research outputs found
Direct genotyping of low abundance Vibrio choleracells from a natural river sample by whole-genome enrichment and sequencing
No full textProgress In Transverse Feedbacks and Related Diagnostics for Hadron Machines
No full textToday Hadron Accelerators with high intensity and high brightness beams increasingly rely on transverse feedback systems for the control of instabilities and the preservation of the transverse emittance. With particular emphasis, but not limited to, the CERN Hadron Accelerator Chain, the progress made in recent years, and the performances achieved are reviewed. Hadron colliders such as the LHC represent a particular challenge as they ask for low noise electronic systems in these feedbacks for acceptable emittance growth. Achievements of the LHC transverse feedback system used for damping injection oscillations and to provide stability throughout the cycle are summarized. This includes its use for abort gap and injection cleaning as well as transverse blow-up for diagnostics purposes. Beyond systems already in operation, advances in technology and modern digital signal processing with increasingly higher digitization rates have made systems conceivable to cure intra-bunch motion. With its capabilities to both acquire beam oscillations and to actively excite motion, transverse feedback systems have a large variety of applications for beam diagnostics purposes
Analysis of bunch by bunch oscillations with bunch trains at injection into LHC at 25 ns bunch spacing
No full textAn MD on August 26, 2011 was dedicated to injection studies of bunch trains with 25 ns spacing and nominal intensity of approximately 1×10(11) protons per bunch. Due to an electrical glitch, the MD was stopped after two attempts of injecting a train of 48 bunches for beam 2. Both injections were aborted after less than 0.1 s. In particular, the first attempt with transverse damper on was dumped after 1000 turns while the second attempt with transverse damper off was dumped after 500 turns only. In this note, an analysis of the bunch by bunch oscillation data recorded with the post-mortem system from the transverse damper is presented. The presented data clearly shows the presence of instabilities that affect mainly the second half of the batch. This is compatible with what would be expected qualitatively in the presence of the electron cloud effect
Gain measurements of the LHC transverse feedback system at 3.5 TeV beam energy
No full textThe damping time of the LHC transverse damper has been determined as a function of the electronic gain setting for a non-colliding bunch at 3.5 TeV. The beam was kicked by the Q-kickers and the oscillation of the bunch recorded turn-by-turn using the damper pick-ups. The damping time is calculated from a fit to the measured data. The obtained values serve as a reference to provide a normalization to the programmed gain function as has been implemented in 2011
LHC Hump observations with ion beams
No full textWe report the observations of the spectra of the ion bunches in the LHC during December 2010 using the LHC damper acquisition board as observation device in order to investigate the so-called "hump" noise signal
Grazing pressure by a bacterivorous flagellate reverses the relative abundance of comamonas acidovorans PX54 and vibrio strain CB5 in chemostat cocultures
No full textPerformance of the LHC Transverse Damper with Bunch Trains
No full textIn 2012 the LHC was operated for Physics with bunch trains at 50 ns spacing. Tests have been performed with the nominal design bunch spacing of 25 ns. The transverse damper has been an essential element to provide beam stability for the multi-bunch beam with up to 1380 bunches used at 50 ns spacing. We report on the experience gained with 50 ns spacing and the improvements in the signal pro- cessing tested for the future 25 ns operation. The increase in bandwidth required for 25 ns spacing constituted a particular challenge. The response of the system was carefully measured and the results used to digitally pre-distort the drive signal to compensate for a drop in gain of the power system for higher frequencies. The bunch-by-bunch data collected from the feedback signal path provided valuable information during the 2012 Physics run that can be further explored for beam diagnostics purposes and instability analysis in the future. Performance estimates are given for the 7 TeV run planned for 2015, at 25 ns bunch spacing
Simulation of Transient Beam-Feedback Interaction and Application to Extraction of CNGS Beam from the SPS
No full textFor present and future high energy proton accelerators, such as the LHC, transverse feedback systems play an essential role in supplying the physics experiments with high intensity beams at low emittances. We developed a simulation model to study the interaction between beam and transverse feedback system in detail, bunch-by-bunch and turn-by-turn, considering the real technical implementation of the latter. A numerical model is used as the non linear behaviour (saturation) and limited bandwidth of the feedback system, as well as the transient nature at injection and extraction, complicates the analysis. The model is applied to the practical case of the CNGS beam in the SPS accelerator. This beam will be ejected from the SPS in two batches causing residual oscillations by kicker ripples on the second batch. This second batch continues to circulate for 2167 turns after the first batch has been extracted and oscillations are planned to be damped by the feedback system. The model can be extended to examine transient effects at injection (LHC), and coupled bunch instability effects can be included
" What you get" — Transverse damper
No full textThe transverse damper (ADT) operation in 2012 was very smooth, routinely switching between different modes and operating the feedback during the entire LHC cycle. We present the new features developed and commissioned in 2012, the selective blow-up, gain gating within the turn and increased bandwidth operation. Several methods were proposed and tested concerning the ADT vs. BBQ cohabitation in order to find the best compromise for machine operation. Performance scaling from 4 TeV to 6.5 TeV, potential limitations at high energy as well as the consolidation and upgrade activities for the long shutdown starting in 2013 (LSl) will also be presented
Benchmarking headtail with electron cloud instabilities observed in the LHC
No full textAfter a successful scrubbing run in the beginning of 2011, the LHC can be presently operated with high intensity proton beams with 50 ns bunch spacing. However, strong electron cloud effects were observed during machine studies with the nominal beam with 25 ns bunch spacing. In particular, fast transverse instabilities were observed when attempting to inject trains of 48 bunches into the LHC for the first time. An analysis of the turn-by-turn bunch-bybunch data from the transverse damper pick-ups during these injection studies is presented, showing a clear signature of the electron cloud effect. These experimental observations are reproduced using numerical simulations: the electron distribution before each bunch passage is generated with PyECLOUD and used as input for a set of HEADTAIL simulations. This paper describes the simulation method as well as the sensitivity of the results to the initial conditions for the electron build-up. The potential of this type of simulations and their clear limitations on the other hand are discussed.After a successful scrubbing run in the beginning of 2011, the LHC can be presently operated with high intensity proton beams with 50 ns bunch spacing. However, strong electron cloud effects were observed during machine studies with the nominal beam with 25 ns bunch spacing. In particular, fast transverse instabilities were observed when attempting to inject trains of 48 bunches into the LHC for the first time. An analysis of the turn-by-turn bunch-bybunch data from the transverse damper pick-ups during these injection studies is presented, showing a clear signature of the electron cloud effect. These experimental observations are reproduced using numerical simulations: the electron distribution before each bunch passage is generated with PyECLOUD and used as input for a set of HEADTAIL simulations. This paper describes the simulation method as well as the sensitivity of the results to the initial conditions for the electron build-up. The potential of this type of simulations and their clear limitations on the other hand are discussed
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