Magnetic Performance of the Main Superconducting Magnets for the LHC

Abstract

Abstract-The field strength and homogeneity of all the LHC superconducting magnets were measured as a part of the production control and qualification process that has taken place during the past four years. In addition to field measurements at room temperature performed on the integral of the production, a significant part of the magnets has been subjected to extensive magnetic measurements at cold. The measurements at cryogenic temperatures, generally performed up to excitation currents of 12 kA corresponding to the ultimate LHC energy of 7.6 TeV, were mainly based on static and dynamic field integral and harmonic measurements. This allowed us to study in detail the DC effects from persistent current magnetization and long-term decay during constant current excitation. These effects are all expected to be of relevance for the field setting and error compensation in the LHC. This paper reports the main results obtained during these tests executed at operating conditions. The integrated field quality is discussed in terms of distribution (average and spread) of the field strength and low-order harmonics as obtained for all the main ring magnet families (dipoles, main and matching quadrupoles). The dependence of field quality on coil geometry, magnet and cable manufacturer is analyzed. A projection of the field quality expected for the critical components in the machine is presented.

Effects of Collar Permeability on the Field Quality of the Large Aperture Quadrupoles for the LHC

“…The model fits the measurements quite well, although the measurements have a larger spread. The additional offset of comes from the persistent currents which account for about 4 units [8]. The error bar for the susceptibility is about 0.0035 in this figure.…”

Magnetic measurement with coils and wires

“…The motor, the bearings of the rotating coil, and the angular encoder are accurately aligned in a straight line with reference to the base plate. [18] describes the mathematical model established on the series measurement of the LHC superconducting magnets, giving an idea of the size of the measurement project. The measuring shaft [17] in the right part is composed of 12 segments 1.15 m long and separated by ceramic bearings resting on the anti-cryostat, therefore rotating off-axis by up to 3 mm with respect to the symmetry axis of the magnet.…”

Advanced Accelerator Magnets for Upgrading the LHC

“…Actually we are not far from the design luminosity, L= 10 34 cm -2 s -1 , considering that luminosity scales linearly with energy. The magnetic system is performing very well, with an excellent reliability and with a field accuracy even better than the design target [6], very much due to the strict Quality Assurance and analysis during construction and test [7], [8]. The magnetic model of the machine [9], incorporating all superconductivity effects, like persistent currents, decay, snap backs, as well as iron yoke saturation and hysteretic effects, is also performing very well, allowing LHC operators to forgetalmost -that the machine requires the adjustment of some 80 magnetic circuits, a good part of them needing to be precise in term of field at better than 10 -4 .…”