Assembly Test of Elastic Averaging Technique to Improve Mechanical Alignment for Accelerating Structure Assemblies in CLIC

The CLIC (Compact LInear Collider) is being studied at CERN as a potential multi-TeV e+e- collider [1]. The manufacturing and assembly tolerances for the required RF-components are important for the final efficiency and for the operation of CLIC. The proper function of an accelerating structure is very sensitive to errors in shape and location of the accelerating cavity. This causes considerable issues in the field of mechanical design and manufacturing. Currently the design of the accelerating structures is a disk design. Alternatively it is possible to create the accelerating assembly from quadrants, which favour the mass manufacturing. The functional shape inside of the accelerating structure remains the same and a single assembly uses less parts. The alignment of these quadrants has been previously made kinematic by using steel pins or spheres to align the pieces together. This method proved to be a quite tedious and time consuming method of assembly. To limit the number of different error sources, a method was introduced to improve the alignment of these pieces, called elastic averaging. This method consists of mechanical features which are directly machined to component to be aligned and uses multiple contacts to “average out” possible random errors caused by the manufacturing. To test this method, a test assembly was designed. This simple design included only two pieces with the elastic averaging assembly features and a reference hole for metrology. The aim of the assembly was to make two-piece-assembly where the reference holes would monitor the alignment. The pieces were measured with a Contact Measuring Machine. A test assembly was measured to verify the use of elastic averaging as an accurate assembly method. The results show that with a proper design this can be achieved with two pieces with a repetition accuracy of 6 µm. The FEM-simulations taking into account the measured geometry support the behaviour of the assembly.