[show abstract][hide abstract] ABSTRACT: Following the incident in one of the main dipole circuits of the Large Hadron Collider (LHC) in September 2008, a detailed analysis of all magnet circuits has been performed by a dedicated task force. This analysis has revealed critical issues in the design of the 13 kA splices between the superconducting dipole and quadrupole magnets. These splices have to be consolidated before increasing the beam energy above 4 TeV and operating the LHC at 6.5-7 TeV per beam. The design of the consolidated 13 kA splices is complete and has been reviewed by an international committee of experts. Also, all other types of superconducting circuits have been thoroughly screened for potential safety issues and several important recommendations were established. They were critically assessed and the resulting actions are presented. In addition to the work on the 13 kA splices, other interventions will be performed during the first long shut-down of the LHC to consolidate globally all superconducting circuits. The associated quality control has been defined. Schedule constraints, repair production rate, available space and resources are presented as well.
[show abstract][hide abstract] ABSTRACT: In the long LHC (Large Hadron Collider) shutdown in 2013 it is foreseen to intervene on all the 13 kA interconnections in order to guarantee the necessary margin and redundancy to provide safe LHC operation at 7 TeV per beam. This implies reinforcement of the present interconnection configuration including a new insulation scheme of the busbars. The purpose of the new insulation model is to provide dielectric insulation with at least the same performance as its predecessor currently installed in the LHC machine, but in addition to contain the Lorentz forces.
[show abstract][hide abstract] ABSTRACT: The accident in the LHC in September 2008 occurred in an interconnection between two magnets of the 13 kA dipole circuit. Successive measurements of the resistance of other interconnects revealed other defective joints, even though the SC cables were properly connected. These defective joints are characterized by a poor bonding between the SC cable and the copper stabilizer in combination with an electrical discontinuity in the copper stabilizer. A quench at the 7-13 kA level in such a joint can lead to a fast and unprotected thermal run-away and hence opening of the circuit. It has therefore been decided to operate the LHC at a reduced and safe current of 6 kA corresponding to 3.5 TeV beam energy until all defective joints are repaired. A task force is reviewing the status of all electrical joints in the magnet circuits and preparing for the necessary repairs. The principle solution is to resolder the worst defective joints and, in addition, to apply an electrical shunt made of copper across all joints with sufficient cross-section to guarantee safe 12-13 kA operation at 7-7.5 TeV. In this paper the various actions that have lead to this solution are presented.
IEEE Transactions on Applied Superconductivity 07/2011; · 1.20 Impact Factor
[show abstract][hide abstract] ABSTRACT: The main busbar interconnection splices of the Large Hadron Collider are assembled by inductive soldering of the Rutherford type cables and the copper profiles of the stabilizer. Following the September 2008 incident, the assembly process and the quality assurance have been improved, with new measurement and diagnostics methods introduced. In the 2008-2009 shutdown the resistance both in the superconducting and in the normal conducting states have been the focus for improvements. The introduction of gamma radiography has allowed the visualization of voids between cable and stabilizer. It is now known that during the standard soldering heating cycle solder is lost from the busbar extremities adjacent to the splice profiles, leaving parts of the cable in poor contact with the stabilizer. A room temperature resistance measurement has been introduced as a simple, non-destructive test to measure the electrical continuity of the splice in its normal conducting state. An ultrasonic test has been performed systematically in order to verify if the vertical gaps between the splice profiles are filled with Sn96Ag4 solder. Visual inspections of the different splice components before and after interconnection have been reinforced. The additional information gained has allowed targeted improvements in the splice production process. Ad-hoc machining of splice components avoids macroscopic gaps, additional soldering foil and copper shims are used in critical areas in order to improve the cable to stabilizer contact.
IEEE Transactions on Applied Superconductivity 07/2011; · 1.20 Impact Factor
[show abstract][hide abstract] ABSTRACT: The major upgrade of the energy and intensity of the existing ISOLDE and REX-ISOLDE facilities at CERN will require the replacement of most of the existing ISOLDE post-acceleration by a superconducting linac based on quarter-wave resonators. The first stage of this upgrade involves the design, construction, installation and commissioning of two high- cryomodules downstream of REX, the existing post-accelerator. Each cryomodule houses five high-beta superconducting cavities and one superconducting solenoid. As well as providing optimum conditions for physics, where the internal active components must remain aligned within tight tolerances, the cryomodules need to function under stringent vacuum and cryogenic conditions. To preserve the RF cavity performance their assembly and sub-system testing will need to be carried out using specifically designed tooling in an ISO class 5 (US Fed. class 100) clean-room. We present the determining factors constraining the design of the high-beta cryomodules together with the design choices that these factors have imposed.
[show abstract][hide abstract] ABSTRACT: Following the analysis of the September 2008 LHC incident, the assembly process and the quality assurance of the main 13 kA interconnection splices were improved, with new measurement and diagnostics methods introduced. During the 2008-2009 shutdown ~5% of these 10 000 splices were newly assembled with these improvements implemented, but essentially maintaining the original design. It is known today that a limiting factor towards 7 TeV operation is the normal conducting resistance of ~15% of the original main 13 kA interconnection splices, associated to the electrical continuity of the copper stabiliser. A “Splices Task Force” has been set up at CERN to evaluate the need for, develop and test design improvements and prepare the implementation of a consolidation campaign. Important issues of splice design, process choice, resources and time requirements are considered.
[show abstract][hide abstract] ABSTRACT: This report summarizes the findings and recommendations of the AT department Task Force established to investigate the 19th September 2008 incident which occurred in sector 3-4 of the LHC. It includes a number of annexes where specific analyses are detailed.
[show abstract][hide abstract] ABSTRACT: The final interconnections of the LHC superconducting magnets in the underground tunnel are performed by a contractor on a result-oriented basis. A consortium of firms was awarded the contract after competitive tendering based on a technical and commercial specification. The implementation of the specific technologies and tooling developed and qualified by CERN has required an important effort to transfer the know-how and implement the follow-up of the contractor. This paper summarizes the start-up phase and the difficulties encountered. The organization and management tools put in place during the ramping-up phase are presented. In addition to contractual adaptations of the workforce, several configuration changes to the workflows were necessary to reach production rates compatible with the overall schedule and with the different constraints: availability of magnets, co-activities with magnets transport and alignment, handling of non-conformities, etc. Also the QA procedures underwent many changes to reach the high level of quality mandatory to ensure the LHC performance. The specificities of this worksite are underlined and first figures of merit of the learning process are presented.
IEEE Transactions on Applied Superconductivity 07/2008; · 1.20 Impact Factor
[show abstract][hide abstract] ABSTRACT: The interconnections between the Large Hadron Collider (LHC) magnets have required some 40 000 TIG welded joints and 65 000 electrical splices. At the level of single joints and splices, non-destructive techniques find limited application: quality control is based on the qualification of the process and of operators, on the recording of production parameters and on production samples. Visual inspection and process audits were the main techniques used. At the level of an extended chain of joints and splices - from a 53.5 m half-cell to a complete 2.7 km arc sector - quality control is based on vacuum leak tests, electrical tests and RF microwave reflectometry that progressively validated the work performed. Subsequent pressure tests, cryogenic circuits flushing with high pressure helium and cool-downs revealed a few unseen or new defects. This paper presents an overview of the quality control techniques used, seeking lessons applicable to similar large, complex projects.
[show abstract][hide abstract] ABSTRACT: As part of the LHC assembly program, the superconducting magnets are interconnected after installation. Electrical continuity between the magnets is ensured via a specifically designed cable junction box which allows the cables to be electrically joined by an automated low temperature soldering technique. The electrical resistance and mechanical strength of the cable junctions depend on the quality of the soldered joint. An ultrasound diagnostic of the soldered junction has been developed to accompany the visual inspection and reinforce the quality control process. Non-standard ultrasound diagnostic techniques, without using matching liquids or gel in the harsh and congested working environment, applied to the sandwich structure of the cable junction box, which presents high ultra-sonic losses due to multiple scattering, have been developed. The equipment and methods implemented are described in detail, together with results of quality control tests made in the production environment.
[show abstract][hide abstract] ABSTRACT: In 2001, the project management decided to perform at CERN the final assembly of the LHC superconducting magnets with cryostat parts and cold masses produced by European Industry in large series. This industrial-like production has required a very significant investment in tooling, production facilities, engineering and quality control efforts, in contractual partnership with a consortium of firms. This unusual endeavour of a limited lifetime represented more than 850,000 working hours spanning over five years, the work being done on a result-oriented basis by the contractor. This paper presents the reasons for having conducted this project at CERN, summarizes the work breakdown structure, the production means and methods, the infrastructure specially developed, the tooling, logistics and quality control aspects of the work performed and the results achieved, in analytical form. Finally, the lessons learnt are outlined.
[show abstract][hide abstract] ABSTRACT: The Large Hadron Collider (LHC) is the next world-facility for the high energy physics community, presently under installation at CERN, Geneva. The main components of the LHC are the twin-aperture high-field superconducting cryomagnets that are powered in series by superconducting Nb-Ti busbars. Along the machine, about 60 000 splices between the superconducting busbars have to be performed in-situ during the interconnection activities. They are carrying a nominal current varying from 600 A to 13 kA depending upon the magnets, at an operating temperature of 1.9 K. Three specific techniques have been developed and optimised for the splicing of the three main types of cables: inductive and resistive soldering, ultrasonic welding. After a brief presentation of the constraints and requirements applying to these junctions, the tooling is described, highlighting the industrialisation aspects. Before their use to interconnect actual cryomagnets in the LHC tunnel, the equipments and procedures follow rigorous qualification to ensure that all the characteristics of the junctions (electrical, mechanical, reliability, ...) are within the specifications. The assessment of the tooling performance is obtained via sample testing of superconducting busbars. Initial results are presented.
Journal of Physics Conference Series 07/2006; 43(1):723.
[show abstract][hide abstract] ABSTRACT: The Large Hadron Collider (LHC) is presently under installation at CERN, Geneva. The approximately 4000 superconducting corrector magnets required by the machine are powered through copper-stabilized Nb-Ti busbars. To interconnect the magnets along the machine, about 50 000 joints between superconducting cables rated at 600 A have to be performed in-situ during the interconnection activities. An ultrasonic welding technique has been developed and optimized by CERN which led to the development of a dedicated machine which was qualified during the assembly of the STRING II, a 110-m chain of cryomagnets assembled as a prototype of the LHC. The realization of the "series" interconnections together with the procurement of the tooling based on functional specifications have been contracted to a consortium of firms. Qualification tests and acceptance criteria in terms of electrical contact resistance, mechanical resistance, reliability and reproducibility have been defined by CERN. This paper presents the tests and some results of the qualification process relevant to the industrialized tooling provided by the contractor. Results of pre-series junctions done in the LHC tunnel are presented together with the perspective for the continuation of the work
IEEE Transactions on Applied Superconductivity 07/2006; · 1.20 Impact Factor
[show abstract][hide abstract] ABSTRACT: The corrector magnets and the main quadrupoles of the LHC dispersion suppressors are powered by a special superconducting line (called auxiliary bus-bars line N), external to the cold mass and housed in a 50 mm diameter stainless steel tube fixed to the cold mass. As the line is periodically connected to the cold mass, the same gaseous and liquid helium cools both the magnets and the line. The final sub-cooling process (from around 4.5 K down to 1.9 K) consists in the phase transformation from liquid to superfluid helium. Heat is extracted from the line through the magnets via their point of junction. In dispersion suppressor zones, approximately 40 m long, the sub-cooling of the line is slightly delayed with respect to the magnets. This might have an impact on the readiness of the accelerator for operation. In order to accelerate the process, a special heat exchanger has been designed. It is located in the middle of the dispersion suppressor portion of the line. Its main function consists in providing a local point of heat extraction, creating two additional lambda fronts that propagate in opposite directions towards the extremities of the line. Both the numerical model and the sub-cooling analysis are presented in the paper for different configurations of the line. The design, manufacturing and integration aspects of the heat exchanger are described.
[show abstract][hide abstract] ABSTRACT: The recent commissioning and operation of the LHC String 2 have given a first experimental validation of the global thermal performance of the LHC lattice cryostat at nominal cryogenic conditions. The cryostat designed to minimize the heat inleak from ambient temperature, houses under vacuum and thermally protects the cold mass, which contains the LHC twin-aperture superconducting magnets operating at 1.9 K in superfluid helium. Mechanical components linking the cold mass to the vacuum vessel, such as support posts and insulation vacuum barriers are designed with efficient thermalisations for heat interception to minimise heat conduction. Heat inleak by radiation is reduced by employing multilayer insulation (MLI) wrapped around the cold mass and around an aluminium thermal shield cooled to about 60 K. Measurements of the total helium vaporization rate in String 2 gives, after substraction of supplementary heat loads and end effects, an estimate of the total thermal load to a standard LHC cell (107 m) including two Short Straight Sections and six dipole cryomagnets. Temperature sensors installed at critical locations provide a temperature mapping which allows validation of the calculated and estimated thermal performance of the cryostat components, including efficiency of the heat interceptions.
[show abstract][hide abstract] ABSTRACT: The numerous complex activities required to prepare the
cryomagnets for the installation in String 2 are described. These
include the configuration of the mechanical interfaces, the conditioning
of the beam tubes, the installation of beam screens and the
instrumentation as well as the final checks. The preparation of the
cryomagnets for String 2 has been a dress rehearsal for the preparation
that the cryomagnets will undergo before their installation in the
tunnel. After a description of the interconnection procedures of the
components for String 2, the tests carried-out to release the String for
operation are described. A brief account of the lessons learnt is also
Particle Accelerator Conference, 2001. PAC 2001. Proceedings of the 2001; 02/2001
[show abstract][hide abstract] ABSTRACT: The interconnections of the Large Hadron Collider (LHC) continuous cryostat have been completed in fall 2007: 1695 interconnections magnet to magnet and 224 interconnections between the continuous cryostat and the cryogenic distribution line have been executed along the 27 km of the LHC. The very tight schedule, the complexity of the interconnection sequence, the strict quality standards applied have required the creation of an ad hoc organization in order to steer and coordinate the activities on the worksite dispersed along the whole accelerator ring. The concatenation of construction and test phases carried out by CERN staff, CERN collaborating institutes and contractors have led to the necessity of a common approach and of a very effective information flow. In this paper, after having recalled the main technical challenges, we review the organizational choices that have been taken and we briefly analyze the development of the worksite in term of allocated resources and production.
[show abstract][hide abstract] ABSTRACT: The LHC is starting operation with beam. The primary goal of CERN and the LHC community is to ensure that the collider is operated efficiently and that it achieves nominal performance in the shortest term. Since several years the community has been discussing the directions for maximizing the physics reach of the LHC by upgrading the experiments, in particular ATLAS and CMS, the LHC machine and the CERN proton injector complex, in a phased approach. The first phase of the LHC interaction region upgrade was approved by Council in December 2007. This phase relies on the mature Nb-Ti superconducting magnet technology with the target of increasing the LHC luminosity to 2 to 3 10^34 cm^-2s^-1, while maximising the use of the existing infrastructure. In this report, we present the goals and the proposed conceptual solutions for the LHC IR Upgrade Phase-I which include the recommendations of the conceptual design review.
[show abstract][hide abstract] ABSTRACT: The interconnections between the cryomagnets and cryogenic utilities in the LHC long Straight Sections constitute the last machine installation activity. They are ensuring continuity of the beam and insulation vacuum systems, cryogenic fluid and electrical circuits and thermal insulation. The assembly is carried out in a constraining tunnel environment with restricted space. Therefore, the assembly sequence has to be well defined and specific tests have to be performed during the interconnection work to secure the reliability of the system and thus to ensure the global accelerator availability. The LHC has 8 long straight insertion zones composed of special cryomagnets involving specific interconnection procedures and QA plans. The aim of this paper is to present the installation and quality assurance procedures implemented for the LHC LSS interconnections. Technologies such as manual and automatic welding and resistive soldering will be described as well as the different quality controls, such as visual and radiographic inspection of welds, electrical checks and leak testing. An evaluation and statistical analysis of the results of the interconnection work will be presented.
[show abstract][hide abstract] ABSTRACT: The Large Hadron Collider (LHC) is the next world-facility for the high energy physics community, presently under construction at CERN, Geneva. The LHC will bring into collisions intense beams of protons and ions. The main components of the LHC are the twin-aperture high-field superconducting cryomagnets that will be installed in the existing 26.7-km long tunnel. They are powered in series by superconducting Nb-Ti cables. Along the machine, about 60 000 joints between superconducting cables must be realised in-situ during the installation. Ten thousands of them, rated at 13 000 A, are involved in the powering scheme of the main dipoles and quadrupoles. To meet the requirements of the cryogenic budget, an electrical resistance at operating temperature (1.9 K) lower than 0.6 nW has to be achieved. The induction soldering technology was selected for this purpose. After a brief introduction to the LHC project, the constraints and requirements are listed. Then, the applied solution is detailed. The splices of the superconducting cables (Rutherford type) form a multi-interface "composite" which, from the electrical point of view, can be modelled as a pair of equipotential surfaces separated by an equivalent conductor with the resistance localized in the interfaces. A simple model is developed and the total cross-splice resistance is compared with the experimentally observed values. Validation of the resistance of splices and the associated heat dissipation to helium at 1.9 K has been successfully performed in STRING2, the prototype of the LHC full cell. This associated to laboratory measurements confirmed the reliability level of splices initially assumed in the whole LHC budget.