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.

The first LHC long shutdown (LS1) was driven by the need to consolidate the 13 kA splices between the main superconducting magnets to safely attain the center of mass design energy of 14 TeV. Access to the splices implies the orbital cutting of welded stainless sleeves. After consolidation, the sleeves are re-welded using a TIG orbital welding process. The welding process has been modified from the original “as-new” installation in order to better adapt to the “as repaired” situation. The intervention has been thoroughly prepared through qualification of the process, organisation of welding teams, their training and their follow-up. For the quality control of the single weld, the joint geometry implies that non-destructive techniques find limited application. Quality control is based on the qualification of the welding process, equipment and operators; the recording of production parameters using new, modern instrumentation; regular process audits and production samples; visual inspection through an official notified body, using novel recording orbital videoscopes. The paper also describes welding and quality control of special intervention cases, with issues of difficult access requiring innovative ad-hoc solutions. This work concerns approximately 10 000 welded joints, 40 engineers and technicians over a period of 18 months. The experience and learning are applicable to similar large, complex projects.

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.

At the European Organisation for Nuclear Research (CERN) the worlds largest particle accelerator ring, the Large Hadron collider (LHC), is being put into operation. It has been found useful to have a tool for diagnosis of the state of components in the interconnection regions of the LHC. This tool, for non-destructive testing (NDT) must work without opening the interconnection elements, without breaking the integrity of the vacuum, and without the need to warm up the sector which would be costly and time consuming. In addition the NDT tool has to be transportable in order to position it anywhere around the 27 km long LHC ring. The approach is an X-Ray inspection with the aim of an unambiguous representation of all structural elements in the interconnection regions of the LHC ring. The minimum criterion is to achieve an inspection result which allows verification of the correct position and integrity of all important components. 3D X-Ray computed tomography (3D CT) would be the ideal solution for such an inspection task. But due to the constraints in the LHC tunnel, especially the very limited space behind the LHC ring it is not possible to move an X-Ray source and a digital XRay detector completely around the interconnections. Therefore it was necessary to develop a mobile 3D X-Ray system which allows for a maximum scanning versatility within the given constraints and provide 3D results based on limited scan angles. Such a mobile X-Ray system is presented in this paper as well as results from the inspections of the LHC ring interconnections. In addition it will be outlined how the approach used in this system could be applied to other applications.

Forty-four kilometers of the LHC beam vacuum system will be equipped with a perforated co-axial liner, the so-called beam screen. Operating between 5 K and 20 K, the beam screen reduces heat loads to the 1.9 K helium bath of the superconducting magnets and minimises dynamic vacuum effects. Constructed from low magnetic permeability stainless steel with a 50 /spl mu/m inner layer of high purity copper, the beam screen must provide a maximum aperture for the beam whilst resisting the induced forces due to eddy currents at magnet quench. The mechanical engineering challenges are numerous, and include stringent requirements on geometry, material selection, manufacturing techniques and cleanliness. The industrial fabrication of these 16 metre long UHV components is now in its prototyping phase. A description of the beam screen is given, together with details of the experimental programme aimed at validating the design choices, and results of the first industrial prototypes.

The two rings of the LHC beam vacuum system have a total length of about 54 km of which almost 48 km will be at 1.9 K, the temperature of the superconducting magnets. The total synchrotron radiation power emitted by the two beams is 0.41 Wm-1. A a so-called beam screen, maintained at a temperature between 5 K and 20 K by gaseous helium flow, is inserted in the magnet cold bore to intercept this power. We discuss the beam screen, magnetic permeability/vapour pressure aspects, beam screen vacuum behaviour, photon-induced gas desorption, intermagnet connection, pressure measurement, warm sections and the insulation vacuum

The chemical treatment of copper cavities carried out prior to cavity coating has been studied in detail. Electropolished and/or chemically polished copper samples have been analysed in terms of the achieved surface morphology, surface cleanliness and RRR value of sputter-deposited niobium films. On the ground of the results obtained, and of the practical constraints of the envisaged application, it is concluded that about 120 p of copper surface should be removed by electropolishing of half-cells, and that a further layer about 20 pm thick should be removed chemically after cavity assembly.