SPECIFICATION OF A SYSTEM OF CORRECTORS FOR THE TRIPLETS AND SEPARATION DIPOLES OF THE LHC UPGRADE

Abstract

The luminosity upgrade of the LHC aims at reducing beta* from 55 cm to 15 cm or beyond. This can be achieved by the ATS [1] scheme and means of new large aperture superconducting triplet (IT) quadrupoles (150 mm), preferably using the Nb3Sn technology in order to keep the gradient reasonably high (140 T/m). The field quality requires careful specification in order to ensure a large enough dynamic aperture (DA). In this context, dedicated corrector magnets are foreseen to provide semi-local corrections of specific multipole components and find the best possible compromise between the demand and what can be realistically achieved by the magnet manufacturer. In this paper the layout and main parameters of the IT corrector package are presented together with the correction strategy. Moreover, the foreseen performance is discussed in detail. CORRECTOR LAYOUT AND STRATEGY The correction strategy follows the one which was established for correcting the field imperfections of the existing triplet and D1 [2, Section 2.2]. The basic principles of the method are described below, with its extension to new multipoles such as a5, b5 and a6 for which no correction is presently available in the nominal LHC. On either side of the interaction point (IP) of the lowβ insertion, generally in between the inner triplet and D1 where the β functions are substantially different in both planes, a dedicated correction coil is installed for each multipole component which is found to be critical for the DA. For the latest version of the HL-LHC optics and layout [3], as for previous versions, the multipole correctors of the triplet and D1 are combined in a correctorpackage installed on the non-IP side of Q3 which contains all multipole correctors, normal and skew, up to order n =6 , except b2 (see Fig. 1). For a given normal or skew field imperfection B ±