Design and Use of Capacitive Force Transducers for Superconducting Magnet Models for the LHC

Capacitive force transducers have been developed and used for monitoring the coil pre-stress during assembly and excitation of several dipole models for LHC. Typically these gauges are strips several tenths of millimeter thick that can be made according to a large variety of geometries. Inserted between two surfaces, they allow to measure the distribution of contact pressures up to 200 MPa from am bient temperature to superfluid helium also in presence of a static magnetic field. The sequence and quality of the manufacturing steps are determining factors in the performance of this kind of gauge s. The paper describes the basic principles, possible configuration geometries, fabrication and calibration procedures of these gauges. Finally the applications of capacitive gauges in the framework o f the R&D programme of superconducting short dipole models for LHC are reviewed and discussed

Modelization of the Thermo-Mechanical Structure of the LHC Main Dipole and Influence on Field Quality

The mechanical structure of the main LHC dipole is analysed. A finite element model is used to estimate the loads and the deformations at cryogenic temperature. The correct setting of the model parameters is crucial to obtain a reliable model to forecast the influence of design and tolerances on field quality. We discuss how the prestress loss from room to cryogenic temperature experimentally observed in the prototypes can be predicted using the finite element model. An estimate of the influence on field quality of deformations and tolerances due to manufacturing is given

Status of the LHC Short Dipole Model Programme

The 1-m model program for the main LHC dipoles is now mainly focussed on double-aperture magnets. In the past years an intensive program based on single-aperture dipoles allowed to select the series-design features among several variants for the coil cross section, the material of the collars and of the coil end spacers, the coil pre-stress and the cable insulation. The recent double-aperture models are dedicated to the fine-tuning of the baseline design and the manufacture of the coil ends. This paper reports about the fabrication and testing of these magnets and the results relevant for the series production of the 15-m long full-size dipole cold masses

A Correlation Study between Geometry of Collared Coils and Normal Quadrupole Multipole in the Main LHC Dipoles

The quality control implemented at all LHC dipole assemblers includes precise mechanical measurements of the geometry of collared coils. A cross-analysis performed between mechanical and magnetic measurements data shows a correlation between collared coils outer dimensions and the normal quadrupole multipole (b2) for one dipole assembler. The profile geometry of the single collars - as determined from 3D measurements at the collar suppliers and CERN - could not account alone for the significant left â right aperture asymmetry observed. This triggered a deeper investigation on different elements of the geometry of single collars. The results of this work show that the relative positioning of the collaring holes, allowing a small bending deformation of collars under the effect of coil pre-stress, is an important effect that generates a b2 multipole at the limit of specification. The study has deepened the understanding of the factors affecting collared coil geometry and field quality. The precision of 3D measurements at the collar suppliers and at CERN has been improved, and a tighter quality control has been introduced at the collar suppliers

Mechanical Behaviour of the Short Models of LHC Main Dipole Magnets

A series of single and twin aperture 1 metre magnet models has been built and tested in the framework of the R&D program of main superconducting dipole magnets for the Large Hadron Collider project. The se models, designed for a nominal field of 8.3 T at 1.8 K, have been constructed to test the performance of SC coils and to optimise various design options for the full length 15 metre long dipoles. T he models have been extensively equipped with a specially developed mechanical instrumentation, enabling both the control of main assembly parameters - like coil azimuthal and axial pre-load, stress i n the outer shrinking cylinder - and also the monitoring of magnet behaviour during cooling and energising, under the action of electromagnetic forces. The instrumentation used, mainly based on strain gauge transducers, is described and the results of mechanical measurements obtained during power tests of the models are discussed and compared with the design predictions based on Finite Element calc ulations

Performance of the 1-m Model of the 6 kA Superconducting Quadrupole for the LHC Insertions

The LHC dispersion suppressors and matching sections will be equipped with individually powered superconducting quadrupoles with an aperture of 56 mm. In order to minimise the cost of the powering circuits, the quadrupole has been designed on the basis of an 8 mm wide NbTi Rutherford-type cable for a nominal current of 5300 A, corresponding to a gradient of 200 T/m at 1.9 K. In order to validate the design options a model magnet program has been launched. In this report we describe the construction features of the first 1-m long magnet, and present its training performance and the results of protection studies

State of the Short Dipole Model Program for the LHC

Superconducting single and twin aperture 1-m long dipole magnets are currently being fabricated at CERN at a rate of about one per month in the framework of the short dipole model program for the LHC. The program allows to study performance improvements coming from refinements in design, components and assembly options and to accumulate statistics based on a small-scale production. The experience thus gained provides in turn feedback into the long magnet program in industry. In recent models initial quenching fields above 9 T have been obtained and after a short training the conductor limit at 2 K is reached, resulting in a central bore field exceeding 10 T. The paper describes the features of recent single aperture models, the results obtained during cold tests and the plans to ensure the continuation of a vigorous model program providing input for the fabrication of the main LHC dipoles

Performance of Five and Six Block Coil Geometries in Short Superconducting Dipole Models for the LHC

A series of similar one meter long superconducting dipole models for the LHC is being manufactured and tested since 1995 for exploring design variants and assembly parameters.Until the end of 1997 all magnets of this series were based on a coil geometry subdividing the conductors in five distinctive winding blocks. In order to cope with new requirements of magnetic field distribution and coil design flexibility, one additional block has been added in the beginning of 1998. A significant number of models of both types have been built and tested, some of them re-built in a different version, adding up in more than 40 models tested so far. The paper reviews the performance of these two different coil designs in terms of manufacture, training behaviour and temperature margins as well as mechanical behaviour and magnetic field quality

Design, Fabrication and Initial Testing of a Large Bore Single Aperture 1 m Long Superconducting Dipole Made with Phenolic Inserts

In the framework of the LHC magnet development programme, a large bore single aperture 1-meter long superconducting dipole has been built in collaboration with HOLEC. The magnet features a single layer coil wound using the LHC main dipole outer layer cable, phenolic inserts, and a keyed two part structural iron yoke. This paper presents the magnetic and mechanical design and optimisation of the magnet. We describe the coil winding and curing, and present the construction and assembly procedures. Finally we report on the mechanical behaviour during assembly and cooling, and present the magnet training behaviour

Status of the Short Dipole Model Program for the LHC

The model program for the LHC main dipoles is dedicated to the study and validation of design variants and assembly parameters to achieve reproducible performance and optimise components and assembly costs. The topics investigated in the last year include the material of the coil end spacers, the use of polyimide films from different manufacturers, the definition of optimum azimuthal and longitudinal coil pre-stress values, shimming of coil ends, collaring around the "cold bore" and different layouts of the yoke ends. This paper presents the main characteristics of such recent models, the results obtained during cold tests and the plans for the final phase of the model program for the LHC dipoles