Long-Range Beam-Beam Compensation in the LHC

To maximize the number of bunches and thereby the luminosity in the LHC, the bunch spacing is as small as 7.5 m. This distance is much less than the length of the low-beta insertion of some 120 m. Multiple head-on collisions around each interaction point are prevented by crossing the beams at an angle. For nominal parameters, this angle is chosen to be 285μm, allowing an average beam separation of 9.5 for the 18 or 19 long-range beam-beam interactions occurring on either side of the two highluminosity insertions (Figure 51). Altogether, for the four LHC interaction regions, about 120 long-range interactions occur at a beam separation close to 9.5 . It was gradually realized from simulations that these interactions are the primary beam dynamics limit of the LHC in collision. This paper reviews a compensation method by wires and the results of investigations obtained so far on numerical and experimental models.