An Improved Insulation System for the LHC Main 13 kA Interconnection Splices

In 2013, a long shutdown of the Large Hadron Collider at CERN will allow comprehensive maintenance plus consolidation of the machine components, in particular of the 13 kA circuits that feed the main superconducting magnets around the 27-km ring. This shutdown will prepare the accelerator for operation at nominal energy, 14 TeV, with adequate margin on the critical performance parameters. An essential part of the consolidation program consists of adding to the 13 kA splices of the magnet interconnects a copper shunt of high RRR(> 300) that will carry the current in the event of a busbar quench. An important R&D program was conducted in 2010 to design a sound solution for the shunt and for an improved insulation system. The development of the insulation system has required iterations aiming at an adequate solution. The functional requirements for the insulation are a breakdown voltage of at least 3.1 kV in superfluid helium and sufficient mechanical strength to withstand stresses of the order of 50 MPa. The insulation system shall provide mechanical restraint for the shunted splices so that their transversal deflection is limited to 0.25 mm. This paper describes the final design of the insulation and the optimization process. The results from dielectric tests and numerical optimization of the insulation cover will be also presented. Finally, the performance of the new insulation will be compared to the previous version.

I. Introduction

In 2013–14 a long shutdown of LHC [1] will be performed for consolidation of the main 13 kA interconnection splices and the related surrounding dielectric insulation. This intervention will allow safe increase towards the nominal LHC operational energy of 7 TeV per beam (14 TeV at the center of mass). The critical aspects when developing an insulation system for the LHC high current superconductive accelerator magnet interconnections are not only given by the knowledge of electrical, mechanical, metallurgical and chemical aspects. The design phase also has to take account of the assembly aspects required to achieve the entire tunnel intervention within the foreseen time schedule of 16 months. Several design iterations were performed during the past three years to successively improve the design of the consolidated splice. This development work was based on four key tasks which were successively iterated according to the design status and the results obtained. The main steps of the development work were as follows: •

Definition of a functional specification;

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Writing of procedures for each consolidation step;

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Execution of mock-up and validation tests;

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Final design acceptance and further installation training based on mock-ups.