14 research outputs found
Comparison of LHC beam loss maps using the transverse damper blow up and tune resonance crossing methods
The LHC collimator settings are qualified regularly via
beam loss maps. In this procedure, the beam is artificially excited to create abnormal loss rates. The transverse
damper blow up and tune resonance crossing methods are
used to increase the betatron amplitude of particles and verify the efficiency of the collimation cleaning and the collimator hierarchy. This paper presents a quantitative comparison of the methods, based on measurements done at
different phases of the LHC machine cycle. The analysis
is done using Beam Loss Monitor (BLM) with integration
times of 1.3 s and 80 ms. The use of the faster BLM data to
study the time evolution of the losses in IR3 and IR7 during
off-momentum loss maps is also presented.peer-reviewe
Collimator impedance measurements in the LHC
The collimation system of the LHC is one of the largest impedance contributors of the machine, in particular for its imaginary part. To evaluate the collimator impedance and its evolution with integrated luminosity, several measurement campaigns were performed along the year 2012, in which collimator jaws were moved back-and-forth leading to significant tune shifts for a nominal intensity bunch in the machine. These observations are compared to the results from HEADTAIL simulations with the impedance model in its current state of development.Asian Committee for Future Accelerators (ACFA),American Physical Society Division of Physics of Beams (APS-DPB),Chinese Academy of Sciences (CAS),European Physical Society Accelerator Group (EPS-AG).peer-reviewe
Lifetime analysis at high intensity colliders applied to the LHC
The beam lifetime is one of the main parameters to define the performance of a collider. In a super-conducting
machine like the LHC, the lifetime determines the intensity
reach for a given collimation cleaning. The beam lifetime
can be calculated from the direct measurement of beam current. However, due to the noise in the beam current signal
only an average lifetime over several seconds can be calculated. We propose here an alternative method, which uses
the signal of the beam loss monitors in the vicinity of the
primary collimators to get the instantaneous beam lifetime
at the collimators. In this paper we compare the lifetime
from the two methods and investigate the minimum lifetime over the LHC cycle for all the physics fills in 2011
and 2012. These data provide a reference for estimates of
performance reach from collimator cleaning.peer-reviewe
Cleaning inefficiency of the LHC collimation system during the energy ramp : simulations and measurements
The cleaning inefficiency of the LHC collimation system for the operational scenarios in 2010-12 has already
been studied in detail at injection and top energy (450 GeV
and 4 TeV respectively). In this paper, results are presented
for the cleaning inefficiency at intermediate energies, simulated using the SixTrack code. The first comparisons with
measured provoked losses are discussed. This study helps
in benchmarking the energy dependence of the simulated
inefficiency and is thus important for the extrapolation to
future operation at higher energies.peer-reviewe
Simulations and measurements of beam losses on LHC collimators during beam abort failures
One of the main purposes of tracking simulations for
collimation studies is to produce loss maps along the
LHC ring, in order to identify the level of local beam
losses during nominal and abnormal operation scenarios.
The SixTrack program is the standard tracking tool used
at CERN to perform these studies.
Recently, it was expanded in order to evaluate the
proton load on different collimators in case of fast beam
failures. Simulations are compared with beam
measurements at 4 TeV. Combined failures are assumed
which provide worst-case scenarios of the load on
tungsten tertiary collimators.peer-reviewe
Experience with high-intensity beam scraping and tail populations at the Large Hadron Collider
The population of beam tails at the Large Hadron Collider (LHC) is a source of concern for the operation at
higher beam energies and intensities when even small fractions of the beam could represent a potential danger is case
of slow or fast losses, e.g. caused by orbit transients or
by collimator movements. Different studies have been performed using the technique of collimator scans to probe
the beam tail population in different conditions. The experience accumulated during the operation at 3.5 TeV and
4 TeV is reviewed.peer-reviewe
Simulations and measurements of beam losses on LHC collimators during beam abort failures
One of the main purposes of tracking simulations for
collimation studies is to produce loss maps along the
LHC ring, in order to identify the level of local beam
losses during nominal and abnormal operation scenarios.
The SixTrack program is the standard tracking tool used
at CERN to perform these studies.
Recently, it was expanded in order to evaluate the
proton load on different collimators in case of fast beam
failures. Simulations are compared with beam
measurements at 4 TeV. Combined failures are assumed
which provide worst-case scenarios of the load on
tungsten tertiary collimators.peer-reviewe
High energy beam impact tests on a LHC tertiary collimator at CERN HiRadMat facility
The correct functioning of the collimation system is crucial to safely operate the LHC. The requirements to handle high intensity beams can be demanding. In this respect, investigating the consequences of LHC particle beams hitting tertiary collimators (TCTs) in the experimental regions is a fundamental issue for machine protection. An experimental test was designed to investigate the robustness and effects of beam accidents on a fully assembled collimator, based on accident scenarios in the LHC. This experiment, carried out at the CERN HiRadMat (High Irradiation to Materials) facility, involved 440 GeV beam impacts of different intensities on the jaws of a horizontal TCT. This paper presents the experimental setup and the preliminary results obtained together with some first outcomes from visual inspection.peer-reviewe
Operating the LHC off-momentum for p-pb collisions
The first high-luminosity p-Pb run at the LHC took place in January-February 2013 at 4 Z TeV energy per beam. The RF frequency difference of proton and Pb is about 60 Hz for equal magnetic rigidities at that energy, which means that beams move to slightly off-momentum, non-central, orbits during physics when frequencies are locked together. The resulting optical perturbations ("beta-beating") restrict the available aperture and required a special correction. This was also the first operation of the LHC with low beta function in all four experiments and it required a specific collimation set up. Predictions from offline calculations of beta-beating correction are compared with measurements during the optics commissioning and collimator set-up.Asian Committee for Future Accelerators (ACFA),American Physical Society Division of Physics of Beams (APS-DPB),Chinese Academy of Sciences (CAS),European Physical Society Accelerator Group (EPS-AG)peer-reviewe
Simulations and measurements of cleaning with 100 MJ beams in the LHC
The CERN Large Hadron Collider is routinely storing proton beam intensities of more than 100 MJ, which puts extraordinary demands on the control of beam losses to avoid quenches of the superconducting magnets. Therefore, a detailed understanding of the LHC beam cleaning is required. We present tracking and shower simulations of the LHC's multi-stage collimation system and compare with measured beam losses, which allow us to conclude on the predictive power of the simulations.Asian Committee for Future Accelerators (ACFA),American Physical Society Division of Physics of Beams (APS-DPB),Chinese Academy of Sciences (CAS),European Physical Society Accelerator Group (EPS-AG)peer-reviewe