Luminosity optimisation by adjusting LHC beta* at collision

To correct the beta * at the main collision points (IP1 and IP5) simultaneously for the two counterrotating proton beams in the LHC a set of specific quadrupoles in the non-common part of the machine is used. Due to the antisymmetric optics, several quadrupoles on each side of the insertion have to be used. The change in the value of beta * is accomplished by changing the k values of the quadrupoles. This set of increments is referred to as beta * tuning knob. The increments were calculated by rematching beta * in a range of +or- 20 % about the nominal value. Linear curves were fitted to the variation of increments to construct a linear tuning knob. This was done for each plane using MAD 8. The linear behaviour and the orthogonality of the knobs were investigated. Different field errors were introduced in the lattice and the correction efficiency of the knobs were studied. (3 refs).