Determination of the Magnetic Axis of a CLIC Drive Beam Quadrupole with respect to External Alignment Targets using a Combination of WPS, CMM and Laser Tracker Measurements

CERN is currently studying the feasibility of building a high energy e⁺ e^{−} linear collider: the CLIC (Compact LInear Collider). One of the engineering challenges is the pre-alignment precision and accuracy requirement on the alignment of the linac components. For example, the magnetic axis of a Drive Beam Quadrupole will need to be aligned within 20 um rms with respect to a straight reference line of alignment. The fiducialisation process which is the determination of the magnetic axis with respect to external alignment targets, that is part of this error budget, will have to be performed at an accuracy never reached before. This paper presents the strategy proposed for the fiducialisation of the Drive Beam quadrupole, based on a combination of CMM measurements, WPS measurements and Laser tracker measurements. The results obtained on a dedicated test bench will be described as well.