Magnetic and Mechanical Design of the Nested Orbit Correctors for HL-LHC

In order to further enhance its discovery potential, LHC will be upgraded in the framework of the High-Luminosity LHC (HL-LHC) project. Among other equipment, the HL-LHC requires the MCBXF orbit correctors, with an aperture diameter of 150 mm. In order to save space, MCBXF consists of two nested dipoles acting on the horizontal and vertical planes. Each dipole shall provide up to 2.1-T central field. The HL-LHC layout needs long (2.5 m) and short (1.5 m) orbit correctors, which will share the same cross section to decrease the cost. This paper is focused on the short version, although some calculations are needed to be extended to the long one due to the fabrication compatibility required between them. First of all, cosine-theta coils are chosen as the most adequate configuration. The main design challenge is the mechanical structure necessary to hold the large torque arising when both dipoles are powered. Magnetic calculations are cumbersome as well. Main difficulties arise from the large aperture, the short straight section, the noticeable iron saturation, and the variable field orientation. Several solutions are evaluated in this paper, and the final conceptual design is presented.