Markus Zerlauth

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.

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.

Testing beam-induced quench levels of LHC superconducting magnets

In the years 2009-2013 the Large Hadron Collider (LHC) has been operated with the top beam energies of 3.5 TeV and 4 TeV per proton (from 2012) instead of the nominal 7 TeV. The currents in the superconducting magnets were reduced accordingly. To date only seventeen beam-induced quenches have occurred; eight of them during specially designed quench tests, the others during injection. There has not been a single beam- induced quench during normal collider operation with stored beam. The conditions, however, are expected to become much more challenging after the long LHC shutdown. The magnets will be operating at near nominal currents, and in the presence of high energy and high intensity beams with a stored energy of up to 362 MJ per beam. In this paper we summarize our efforts to understand the quench levels of LHC superconducting magnets. We describe beam-loss events and dedicated experiments with beam, as well as the simulation methods used to reproduce the observable signals. The simulated energy deposition in the coils is compared to the quench levels predicted by electro-thermal models, thus allowing to validate and improve the models which are used to set beam-dump thresholds on beam-loss monitors for Run 2.

A Statistical Analysis of Electrical Faults in the LHC Superconducting Magnets and Circuits

The large hadron collider (LHC) at CERN has been operating and generating physics experimental data since September 2008, and following its first long shut down, it has entered a second, 4-year-long physics run. It is to date the largest superconducting installation ever built, counting over 9000 magnets along its 27-km long circumference. A significant operational experience has been accumulated, including the occurrence and consequences of electrical faults at the level of the superconducting magnets, as well as their protection and instrumentation circuits. The purpose of this paper is to provide a first overview of the most common electrical faults and their frequency of occurrence in the first years of operation, and to perform a statistical analysis that can provide reference values for future productions of similar dimensions and nature.

submitter : Resistance of Splices in the LHC Main Superconducting Magnet Circuits at 1.9 K

The electrical interconnections between the LHC main magnets are made of soldered joints (splices) of two superconducting Rutherford cables, stabilized by a copper busbar. In 2009, a number of splices was found not properly stabilized and could have suffered a thermal runaway in case of quench at high current. The LHC was, therefore, operated at reduced energy and all joints were continuously monitored by a newly installed layer of the quench protection system. During the first long shutdown (LS1) in 2013/14, the high-current busbar joints were consolidated to allow us a safe operation of the LHC at its design energy, i.e., 14-TeV center-of-mass. The superconducting magnets and circuits consolidation project has coordinated the consolidation of the 10306 13-kA busbar splices. Since 2015, the LHC is successfully operated at an energy of 13-TeV center-of-mass. This paper will briefly describe the applied analysis method and will present the results and comparisons of the Rutherford-cable splice resistance measurements at 1.9 K before and after LS1, based on an unprecedented amount of information gathered during long-term operation of superconducting high-current joints. A few outliers that are still present after the splice consolidation will also be shortly discussed.

Machine Protection, Interlocks and Availability

Chapter 7 in High-Luminosity Large Hadron Collider (HL-LHC) : Preliminary Design Report. The Large Hadron Collider (LHC) is one of the largest scientific instruments ever built. Since opening up a new energy frontier for exploration in 2010, it has gathered a global user community of about 7,000 scientists working in fundamental particle physics and the physics of hadronic matter at extreme temperature and density. To sustain and extend its discovery potential, the LHC will need a major upgrade in the 2020s. This will increase its luminosity (rate of collisions) by a factor of five beyond the original design value and the integrated luminosity (total collisions created) by a factor ten. The LHC is already a highly complex and exquisitely optimised machine so this upgrade must be carefully conceived and will require about ten years to implement. The new configuration, known as High Luminosity LHC (HL-LHC), will rely on a number of key innovations that push accelerator technology beyond its present limits. Among these are cutting-edge 11-12 tesla superconducting magnets, compact superconducting cavities for beam rotation with ultra-precise phase control, new technology and physical processes for beam collimation and 300 metre-long high-power superconducting links with negligible energy dissipation. The present document describes the technologies and components that will be used to realise the project and is intended to serve as the basis for the detailed engineering design of HL-LHC.

Reliable Software Development for Machine Protection Systems

The Controls software for the Large Hadron Collider (LHC) at CERN, with more than 150 millions lines of code, resides amongst the largest known code bases in the world. Industry has been applying Agile software engineering techniques for more than two decades now, and the advantages of these techniques can no longer be ignored to manage the code base for large projects within the accelerator community. Furthermore, CERN is a particular environment due to the high personnel turnover and manpower limitations, where applying Agile processes can improve both, the codebase management as well as its quality. This paper presents the successful application of the Agile software development process Scrum for machine protection systems at CERN, the quality standards and infrastructure introduced together with the Agile process as well as the challenges encountered to adapt it to the CERN environment.