The LHC machine status, calibration run and commissioning plans

The status of the ongoing LHC installation is reported with some attention given to the long straight sections around the experiments. An overview of the proposed commissioning schedule for 2007 and 2008 presented. This schedule includes a calibration run at the end of 2007 which aims to deliver collisions at 450 GeV beam energy. The details of this run and planned beam conditions are summarised. The full commissioning to 7 TeV will be a challenging exercise and an overview of the plans for 2008 is given. Finally, the beam related issues associated with the LHC upgrade are briefly introduced

Chromaticity decay due to superconducting dipoles on the injection plateau of the Large Hadron Collider

It is well known that in a superconducting accelerator a significant chromaticity drift can be induced by the decay of the sextupolar component of the main dipoles. In this paper we give a brief overview of what was expected for the Large Hadron Collider (LHC) on the grounds of magnetic measurements of individual dipoles carried out during the production. According to this analysis, the decay time constants were of the order of 200 s: since the injection in the LHC starts at least 30 minutes after the magnets are at constant current, the dynamic correction of this effect was not considered to be necessary. The first beam measurements of chromaticity showed significant decay even after a few hours. For this reason, a dynamic correction of decay on the injection plateau was implemented based on beam measurements. This means that during the injection plateau the sextupole correctors are powered with a varying current to cancel out the decay of the dipoles. This strategy has been implemented successfully. A similar phenomenon has been observed for the dependence of the decay amplitude on the powering history of the dipoles: according to magnetic measurements, also in this case time constants are of the order of 200 s and therefore no difference is expected between a one hour or a ten hours flattop. On the other hand, the beam measurements show a significant change of decay for these two conditions. For the moment there is no clue of the origin of these discrepancies. We give a complete overview of the two effects, and the modifications that have been done to the field model parameters to be able to obtain a final chromaticity correction within a few units.peer-reviewe

Hysteresis Effects of MCBX Magnets on the LHC Operation in Collision

The Large Hadron Collider beams are brought into collision by superconducting orbit corrector magnets which generate the parallel separation and crossing angles at the interaction points during the different cycle phases. Unfortunately, the magnetic field errors that result from hysteresis effects in the operation region of these magnets lead to unwanted orbit perturbations. In a previous paper, it has been shown that these effects are within the perturbations coming from beam-beam interactions for the MCBC and the MCBY magnets but are significant in the case of the MCBX magnets. This paper presents a refined model of their field in the frame of the Field Description for the LHC (FiDeL); the results obtained from new magnetic measurements in cold conditions to test the model; the powering mechanism employed to maximize their field reproducibility; and the impact the modelling error is predicted to have on the LHC orbit in phase 1

Hysteresis effects of MCBX magnets on the LHC operation in collision

The Large Hadron Collider beams are brought into collision by superconducting orbit corrector magnets which generate the parallel separation and crossing angles at the interaction points during the different cycle phases. Unfortunately, the magnetic field errors that result from hysteresis effects in the operation region of these magnets lead to unwanted orbit perturbations. In a previous paper, it has been shown that these effects are within the perturbations coming from beam-beam interactions for the MCBC and the MCBY magnets but are significant in the case of the MCBX magnets. This paper presents a refined model of their field in the frame of the Field Description for the LHC (FiDeL); the results obtained from new magnetic measurements in cold conditions to test the model; the powering mechanism employed to maximize their field reproducibility; and the impact the modelling error is predicted to have on the LHC orbit in phase 1.peer-reviewe

Beam Based Optimization Of The Squeeze In The LHC

The betatron squeeze is a critical operational phase for the LHC because it is carried out at top energy, with the maximum stored energy and with reduced aperture mar- gins in the superconduting triplets. A stable operation with minimum beam losses must be achieved in order to ensure a safe and efficient operation. The operational experience at the LHC showed that this is possible. The operation in 2010 is reviewed. In particular, orbit, tune and chromatic- ity measurements are investigated and correlated to beam losses. Different optimizations are then proposed towards a more efficient and robust operation. The improvements obtained for the operation in 2011 are presented

The FiDel model at 7 TeV

After the long shut down of 2013-2014, the LHC energy will be pushed toward 7 TeV. In this range of energy, the main magnets will enter a new regime. For this reason, this paper will present a detailed study of the performance of the FiDeL model that could be critical for the operation in 2015. In particular this paper will study the saturation component and its precision in the model, the errors due to the hysteresis, and an estimate of the dynamic effects for the 7 TeV operation.peer-reviewe

The LHC Sector Test

The proposal to inject beam into a sector of the partially completed LHC is presented. The test will provide an important milestone, force preparation of a number of key systems, and allow a number of critical measurements with beam. The motivation for the test is discussed, along with the proposed beam studies, the radiation issues and the potential impact on ongoing installation. The demands on the various accelerator systems implicated are presented along with the scheduling of the preparatory steps, the test itself and the recovery phase

Commissioning of Ramp and Squeeze at the LHC

The energy ramp and the betatron squeeze at the CERN Large Hadron Collider (LHC) are particularly critical oper- ational phases that involve the manipulation of beams well above the safe limit for damage of accelerator components. In particular, the squeeze is carried out at top energy with reduced quench limit of superconducting magnets and re- duced aperture in the triplet quadrupoles. In 2010, the commissioning of the ramp from 450 GeV to 3.5 TeV and the squeeze to 2 m in all the LHC experiments have been achieved and smoothly became operational. In this paper, the operational challenges associated to these phases are discussed, the commissioning experience with single- and multi-bunch operation is reviewed and the overall perfor- mance is discusse

Genomic Comparison of Indigenous African and Northern European Chickens Reveals Putative Mechanisms of Stress Tolerance Related to Environmental Selection Pressure

Global climate change is increasing the magnitude of environmental stressors, such as temperature, pathogens, and drought, that limit the survivability and sustainability of livestock production. Poultry production and its expansion is dependent upon robust animals that are able to cope with stressors in multiple environments. Understanding the genetic strategies that indigenous, noncommercial breeds have evolved to survive in their environment could help to elucidate molecular mechanisms underlying biological traits of environmental adaptation. We examined poultry from diverse breeds and climates of Africa and Northern Europe for selection signatures that have allowed them to adapt to their indigenous environments. Selection signatures were studied using a combination of population genomic methods that employed FST, integrated haplotype score (iHS), and runs of homozygosity (ROH) procedures. All the analyses indicated differences in environment as a driver of selective pressure in both groups of populations. The analyses revealed unique differences in the genomic regions under selection pressure from the environment for each population. The African chickens showed stronger selection toward stress signaling and angiogenesis, while the Northern European chickens showed more selection pressure toward processes related to energy homeostasis. The results suggest that chromosomes 2 and 27 are the most diverged between populations and the most selected upon within the African (chromosome 27) and Northern European (chromosome 2) birds. Examination of the divergent populations has provided new insight into genes under possible selection related to tolerance of a population’s indigenous environment that may be baselines for examining the genomic contribution to tolerance adaptions