Influence of Mechanical Tolerances on Field Quality in the LHC Main Dipoles

We evaluate the influence of mechanical tolerances on the field quality in the LHC dipoles. We show that the most relevant effect is due to tolerances on the coil and on the internal part of the collars. The sensitivities of the field error multipoles on the mechanical tolerances are worked out using a finite element model of the dipole cross section. A MonteCarlo method is used to simulate the overall effect of both collar and coil tolerances on field quality. Correlation between random multipoles is worked out, and a comparison with the target table of the LHC field errors is given

A Method to Evaluate the Field-Shape Multipoles Induced by Coil Deformations

A semi-analytical method to evaluate the effect of coil de-formations on the field-shape imperfections of the LHC dipole is presented. The deformation induced by the collaring procedure and by the thermal stresses is evaluated numerically with a finite element code. The vector field of mechanical displacements is approximated with truncated Taylor and Fourier series. The fitting function agrees with the numerical data to within less that 10 mm. The decom-position in modes of the truncated series permits identification of displacements which are dangerous for the multi-polar content and how they could be cured. An application to compare two designs of the LHC dipole is given

[Incidence and management of infusion reactions to infliximab in 186 italian patients with rheumatoid arthritis: the Padua experience].

Objective: We report the incidence and treatment of infusion reactions to infliximab, a chimeric monoclonal IgG1 antibody against tumor necrosis factor a, in a large cohort of patients with rheumatoid arthritis. Patients and methods: One hundred eighty six patients with rheumatoid arthritis treated with infliximab for a total of 216.6 patient years were retrospectively evaluated. Patients received 2160 infliximab infusions at the Division of Rheumatology at the University Hospital of Padua from May, 2000 to April, 2004. Specific treatment protocols for initial and subsequent acute infusion reactions were followed and the outcomes documented. Results: The overall incidence of infusion reactions to infliximab was 0.8% (19 out of 2160 of infusions), affecting 10.2% of patients (19 out of 186). Mild, moderate, or severe acute reactions occurred in 0.1% (3 of 2160), 0.6% (13 of 2160), and 0.04% (1 of 2160) of infliximab infusions, respectively. Delayed infusion reactions occurred in 0.09% (2 of 2160) of infusions. Use of specific treatment protocols resulted in rapid resolution of all acute reactions to infliximab. With a prophylaxis protocol, all patients who experienced an initial mild acute reaction were able to receive additional infusions. Conclusions: Using appropriate treatment protocols, infliximab infusion reactions were effectively treated and prevented in patients with mild acute reactions upon retreatment. In the case of moderate to severe infusion reactions, the risks and the benefits of the continuation of infliximab therapy need to be carefully considered

Field quality in the ends of the Large Hadron Collider main dipole: Measurements and correlation to industrial assembly procedures

Magnetic field measurements are an important tool to monitor the LHC main dipole production. In this paper we analyse the data relative to a few tens of collared coils produced for the pre-series dipoles. Strong systematic differences between field at the magnet extremities are observed. Moreover, three different families of coil ends corresponding to the different coil manufacturers can be singled out. A 3D model of the coil ends is used to understand these differences in terms of the assembly parameters and the industrial procedures. We analyse the production trends in order to characterize the geometric parameters and the critical components for the field quality. The field components in the dipole ends are finally compared to the beam dynamics budget allowed for the whole dipole

Modeling of Coil Pre-stress Loss During Cool-down in the Main Dipoles of the Large Hadron Collider

We describe a finite element mechanical model of the main LHC dipole, based on the geometry and on the properties of its components; coil characteristics are derived from measurements on stacks of conductors. We show how to define equivalent properties of cable blocks that take into account the collaring procedure when it is not explicitly modelled. Numerical results are then compared to experimental measurements of loads and deformations in dipole prototypes. At cryogenic temperature, equivalent properties are used to implement in the model a pressure- dependent thermal contraction factor observed in stack measurements. This allows to forecast the large pre-stress loss during the cool-down observed in the LHC dipole prototypes

Analysis of Conductor Displacements in the Coil of the LHC Main Dipole by Speckle Interferometry

Magnetic field quality in superconducting magnets mostly depends on conductor position in operational conditions (under pressure, at 1.9 K). For the case of the LHC main magnets, the conductor layout must agree with the nominal design within less than 0.05 mm to met the field quality specifications. Finite element models are a numerical tool to forecast loads and deformations of mechanical structures, and can be used to evaluate conductor displacements. To verify the FEM response at room temperature, we made displacement measurements using speckle interferometer on a short sample of the dipole coils. Experimental results are compared with the numerical calculations, allowing a stringent test of the most critical features of the FEM (interfaces between different materials and coil properties)

Trends in Field Quality along the Production of the LHC Dipoles and Differences among Manufacturers

More than two thirds of the dipoles of the Large Hadron Collider have been manufactured and their magnetic field has been measured at room temperature. In this paper we make a review of the trends that have been observed during the production. In some cases, the trends were traced back to displacements of conductors with respect to the nominal lay-out. The analysis allows detecting the most critical zones in the superconducting coil as far as field quality is concerned. The second part of the paper makes the point of the observed differences in field quality between the three manufacturers. The analysis allows evaluating which multipoles are more affected, what magnitudes of displacements are necessary to explain these differences (the manufacturers all producing the same baseline), and what could be the origin of such differences

Field-shape imperfections of the CERN-LHC dipole arising from mechanical deformations and component tolerances

The stability of the geometry of the superconducting coils is essential to the field homogeneity of the LHC dipole magnets. Mechanical stresses during coil assembly, thermal stresses during cool-down and electromagnetic stresses during operation are the source of deformations of the coil geometry. Additional sources of field-shape errors are the dimensional tolerances of the magnet components and of the manufacturing and assembly tooling. To provide a realistic evaluation of the field-shape imperfections of the LHC dipoles arising from the above effects, appropriate finite-element computations were carried out to model the dipole cross-section in presence of stresses and a first statistical simulation of the effect of the manufacturing tolerances was performed as well

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