J. Ph. Tock

Nondestructive Testing and Quality Control of the LHC Main Interconnection Splices

The Large Hadron Collider (LHC) main interconnection splices consist of Rutherford-type cable splice and busbar stabilizer splices. Busbar stabilizer splices have been consolidated during the first long LHC shutdown by soldering additional Cu shunts. In view of the large number of quality controls (QCs) that were integrated in the splice consolidation process, efficient and unambiguous QC procedures needed to be developed. Direct-current electrical resistance measurements have been selected for the control of the busbar splices and the individual shunts. About 400 000 resistance measurements performed at room temperature before and after each consolidation step have been analyzed. The resistance of the consolidated splices is comparable with the resistance of continuous busbars without splice. Resistance changes during the consolidation process correspond to those calculated from the changes in Cu cross-sectional area.

Industrial tooling and methods for the junctions of the superconducting busbars in the interconnections between the LHC cryomagnets

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.

Status of the Consolidation of the LHC Superconducting Magnets and Circuits

The first LHC long shutdown (LS1) started in February 2013. It was triggered by the need to consolidate the 13 kA splices between the superconducting magnets to allow the LHC to reach safely its design energy of 14 TeV center of mass. The final design of the consolidated splices is recalled. 1695 interconnections containing 10 170 splices have to be opened. In addition to the work on the 13 kA splices, the other interventions performed during the first long shut-down on all the superconducting circuits are described. All this work has been structured in a project, gathering about 280 persons. The opening of the interconnections started in April 2013 and consolidation works are planned to be completed by August 2014. This paper describes first the preparation phase with the building of the teams and the detailed planning of the operation. Then, it gives feedback from the worksite, namely lessons learnt and adaptations that were implemented, both from the technical and organizational points of view. Finally, perspectives for the completion of this consolidation campaign are given.

Consolidation of the LHC Superconducting Magnets and Circuits

The first Large Hadron Collider (LHC) Long Shutdown (LS1) started in February 2013. It was triggered by the need to consolidate the 13-kA splices between the superconducting magnets to allow the LHC to reach safely its design energy of 14 TeV center of mass. The Superconducting Magnets and Circuits Consolidation (SMACC) project has principally covered the consolidation of the 10170 13-kA splices but also other activities linked to the superconducting magnets such as the exchange of 18 main cryomagnets, the installation of the additional safety relief devices, the repair of known helium leaks, and other consolidation activities. All these works have been structured in a project, gathering about 280 persons. The opening of the interconnections started in April 2013 and consolidation works were completed by September 2014. This paper first describes the preparation phase with the building of the teams and the detailed planning of the operations. Then, this paper carried out is summarized, and the main results achieved are presented. Finally, it gives feedback from the worksite, namely lessons learnt and adaptations that were implemented, both from the technical and organizational points of view.

Retraining of the 1232 Main Dipole Magnets in the LHC

The Large Hadron Collider (LHC) contains eight main dipole circuits, each of them with 154 dipole magnets powered in series. These 15-m-long magnets are wound from Nb-Ti superconducting Rutherford cables, and have active quench detection triggering heaters to quickly force the transition of the coil to the normal conducting state in case of a quench, and hence reduce the hot spot temperature. During the reception tests in 2002-2007, all these magnets have been trained up to at least 12 kA, corresponding to a beam energy of 7.1 TeV. After installation in the accelerator, the circuits have been operated at reduced currents of up to 6.8 kA, from 2010 to 2013, corresponding to a beam energy of 4 TeV. After the first long shutdown of 2013-2014, the LHC runs at 6.5 TeV, requiring a dipole magnet current of 11.0 kA. A significant number of training quenches were needed to bring the 1232 magnets up to this current. In this paper, the circuit behavior in case of a quench is presented, as well as the quench training as compared to the initial training during the reception tests of the individual magnets.

Consolidation of the 13- kA Superconducting Magnet Circuits of the LHC at CERN

The first long shutdown (LS1) of the LHC machine at CERN started in February 2013. The main trigger for LS1 was the consolidation of the bus bar joints in the 13-kA superconducting magnet circuits. Before LS1, the copper continuity of these joints was not sufficiently good to ensure a safe passage of the current in case of a quench in the superconducting cable at currents larger than 7-8 kA. The consolidation mainly consists in adding shunts made of high conductivity copper across each joint connecting the bus bars of the neighboring magnets in order to ensure the copper continuity. After LS1, the LHC can then be operated up to the original nominal conditions, i.e., a collision energy of 14 TeV. There are 1695 interconnects, each containing six 13-kA joints, of which two belong to the main dipole circuit and four to the main quadrupole circuits. This paper describes the different steps of the consolidation work performed on the 10 170 magnet-to-magnet joints. The work on the splices proper has been organized in the form of a train made of six production teams, all together consisting of about 90 persons, including operators, supervision, and quality assurance. The work flow is managed with the help of a web-based tool called WISH. This paper describes as well the quality control and quality assurance methods put in place to ensure the quality of the work throughout the project, and it summarizes the benefits of the consolidation work in terms of copper continuity, operation margin, and robustness of the new insulation system.