Beam Based Alignment of the LHC Transfer Line Collimators

At LHC injection energy the aperture available in the transfer lines and in the LHC is small and the intensities of the injected beams are an order of magnitude above the damage level. The setting of protection elements such as the transfer line collimators is therefore very critical; mechanical and optical tolerances must be taken into account to define the nominal setting. Being able to measure and control the collinearity of the collimator jaws with the beam relaxes the requirement on the settings considerably. A method to measure angular misalignment of the collimator jaws in the transfer line based on a transmission measurement is discussed. Simulations have been made and a test of principle has been carried out during the 2004 commissioning of the transfer line TI 8.