J. Uythoven

Protection of the CERN Large Hadron Collider

TheLargeHadronCollider(LHC)atCERNwillcollidetwocounter- rotating proton beams, each with an energy of 7TeV. The energy stored in the superconducting magnet system will exceed 10GJ, and each beam has a stored energy of 362MJ which could cause major damage to accelerator equipment in the case of uncontrolled beam loss. Safe operation of the LHC will therefore rely on a complex system for equipment protection. The systems for protection of the superconducting magnets in case of quench must be fully operational before powering the magnets. For safe injection of the 450GeV beam into the LHC, beam absorbers must be in their correct positions and specific procedures must be applied. Requirements for safe operation throughout the cycle necessitate early detection of failures within the equipment, and active monitoring of the beam with fast and reliable beam instrumentation, mainly beam loss monitors (BLM). When operating with circulating beams, the time constant for beam loss after a failureextendsfrom ≈mstoafewminutes—failuresmustbedetectedsufficiently early and transmitted to the beam interlock system that triggers a beam dump. It is essential that the beams are properly extracted on to the dump blocks at the end of a fill and in case of emergency, since the beam dump blocks are the only elements of the LHC that can withstand the impact of the full beam.

Improvements to power couplers for the LEP2 superconducting cavities

Power couplers for the 352 MHz LEP2 superconducting RF cavities have been plagued by vacuum and electron outbursts which are attributed to multipacting. Processing of these couplers has been a lengthy operation which was often needed again after high power running even if only for a relatively short time. We report here on recent progress made in improved production methods of coupler parts and special treatment of surfaces, as well as practical tests and simulations of geometrical coupler modifications.

Reliability Assessment of the LHC Machine Protection System

A large number of complex systems will be involved in ensuring a safe operation of the CERN Large Hadron Collider, such as beam dumping and collimation, beam loss and position monitors, quench protection, powering interlock and beam interlock system. The latter will monitor the status of all other systems and trigger the beam abort if necessary. While the overall system is expected to provide an extremely high level of protection, none of the involved components should unduly impede machine operation by creating physically unfounded dump requests or beam inhibit signals. This paper investigates the resulting trade-off between safety and availability and provides quantitative results for the most critical protection elements.

Commissioning of the LHC Beam Transfer Line TI 8

The first of the two LHC transfer lines was commissioned in autumn 2004. Beam reached an absorber block located some 2.5 km downstream of the SPS extraction point at the first shot, without the need of any threading. The hardware preparation and commissioning phase will be summarised, followed by a description of the beam tests and their results regarding optics and other line parameters, including the experience gained with beam instrumentation, the control system and the machine protection equipment.

Designing and building a collimation system for the high-intensity LHC beam

The Large Hadron Collider (LHC) will collide proton beams at 14 TeV c.m. with unprecedented stored intensities. The transverse energy density in the beam will be about three orders of magnitude larger than previously handled in the Tevatron or in HERA, if compared at the locations of the betatron collimators. In particular, the population in the beam halo is much above the quench level of the superconducting magnets. Two LHC insertions are dedicated to collimation with the design goals of preventing magnet quenches in regular operation and preventing damage to accelerator components in case of irregular beam loss. We discuss the challenges for designing and building a collimation system that withstands the high power LHC beam and provides the required high cleaning efficiency. Plans for future work are outlined.

Beam Stability of the LHC Beam Transfer Line TI 8

Injection of beam into the LHC at 450 GeV/c proceeds over two 2.7 km long transfer lines from the SPS. The small aperture of the LHC at injection imposes tight constraints on the stability of the beam transfer. The first transfer line TI 8 was commissioned in the fall of 2004 with low intensity beam. Since the beam position monitor signal fluctuations were dominated by noise with low intensity beam, the beam stability could not be obtained from a simple comparison of consecutive trajectories. Instead model independent analysis (MIA) techniques as well as scraping on collimators were used to estimate the intrinsic stability of the transfer line. This paper presents the analysis methods and the resulting stability estimates.

UFOs in the LHC after LS1

UFOs (“Unidentified Falling Objects”) are potentially a major luminosity limitation for nominal LHC operation. With large-scale increases of the BLM thresholds, their impact on LHC availability was mitigated in the second half of 2011. For higher beam energy and lower magnet quench limits, the problem is expected to be considerably worse, though. Therefore, in 2011, the diagnostics for UFO events were significantly improved, dedicated experiments and measurements in the LHC and in the laboratory were made and complemented by FLUKA simulations and theoretical studies. In this paper, the state of knowledge is summarized and extrapolations for LHC operation after LS1 are presented. Mitigation strategies are proposed and related tests and measures for 2012 are specified.

LHC machine protection

For nominal beam parameters at 7 TeV/c each of the two LHC proton beams has a stored energy of 362 MJ threatening to damage accelerator equipment in case of uncontrolled beam loss. The energy stored in the magnet system at 7 TeV/c will exceed 10 GJ. In order to avoid damage of accelerator equipment, complex machine protection systems are required. Magnet protection and powering interlock systems must be operational already before commissioning the magnet powering system. Beam operation, throughout the operational cycle from injection to colliding beams, requires fully operational protection systems, including beam interlock systems, beam dumping system, beam instrumentation (mainly beam loss monitors) as well as collimators and beam absorbers. Details of LHC machine protection have been presented on several occasions and the systems involved in protection are well documented. This paper gives an overview of LHC machine protection, discusses the progress with the implementation and presents first results from the commissioning of some systems.

Reliability Analysis of the LHC Beam Dumping System

The design of the Beam Dumping System of the Large Hadron Collider at CERN is aimed at ensuring a safe beam extraction and deposition under all circumstances. The system includes redundancy and continuous surveillance for most of its parts. Extensive diagnostics after each beam dumping action will be performed to reduce the risk of a faulty operation upon the subsequent dump trigger. Calculations of the system’s safety and availability are presented for the beam dumping kickers and septa magnets.

LHC beam dumping system: extraction channel layout and acceptance

The LHC beam dumping system must safely abort the LHC beams under all conditions, including those resulting from abnormal behaviour of machine elements or subsystems of the beam dumping system itself. The extraction channels must provide sufficient aperture both for the circulating and extracted beams, over the whole energy range and under various beam parameters. These requirements impose tight constraints on the tolerances of various extraction channel components, and also on the allowed range of beam positions in the region of these components. Operation of the beam dumping system under various fault states has been considered, and the resulting apertures calculated. After describing briefly the beam dumping system and the extraction channel geometry, the various assumptions made in the analysis are presented, before deriving tolerance limits for the relevant equipment and beam parameters.