CERN, Geneva, Switzerland
DCOM-iTEAM-UPV, Valencia, Spain
IFIC, Valencia, Spain
The CLIC project, currently under study at CERN is an electron-positron collider at 3 TeV centre-of-mass energy and luminosity of 2*1034 cm-2s−1. Achieving such luminosity requires a beam dimension of 1 nm in the vertical plane and high beam stability. The TD24 is a traveling wave structure operating at 12 GHz designed to reach 100 MV/m at constant gradient. It consists of two coupling cells and 24 disks. The RF is coupled from cell to cell though an iris of 5.5 mm. To minimize the occurrence of wake-fields and minimize the emittance growth Δεy below 5%, the pre-alignment precision of the electrical centre of the accelerating structure (AS) on its support has to be better than 7 μm. Following, the AS is actively aligned with beam using the wake-field monitor (WFM) signals, with a resolution of 3.5 μm. A test bench for laboratory measurements has been designed and exploits the asymmetry created by RF scattering parameters of an off-centre conductive wire, stretched to locate the electromagnetic centre of the AS. Simulations and preliminary measurement results are presented.
CERN, Geneva, Switzerland
PACMAN, a study on Particle Accelerator Components' Metrology and Alignment to the Nanometre scale, is an Innovative Doctoral Program, funded by the European Commission, hosted by CERN. The objective is to propose new methods allowing the determination of the reference axis of accelerator components with respect to external alignment targets. A test bench, using real components of the Compact Linear Collider (CLIC) study, will demonstrate the feasibility of the solutions developed with micrometric accuracy. The study concerns the methods developed using a stretched wire to determine the magnetic axis of small aperture magnets, the electrical centre of a 15 GHz RF-BPM or the electro-magnetic axis of an accelerating cavity. Solutions are also carried out to measure the position of the wire with respect to the external alignment targets, using a 3D Coordinate Measuring Machine or portable alternatives based on Frequency Scanning Interferometry or micro-triangulation. Other systems developed are also taken into account: a nano-positioning system to validate the nanometric resolution of the BPM and a dedicated seismic sensor to characterize the environment during the measurements.
CERN, Geneva, Switzerland
Università di Pisa, Pisa, Italy
For the Compact LInear Collider (CLIC) project at CERN, maintaining low emittance beams, as they are transported along the two independent 10-20 km long main linacs, is crucial. The beam trajectory therefore has to be very well aligned to the magnetic centre of the quadrupole magnets. A series of microwave cavity beam position monitors (BPM) is foreseen to detect the position of the beam along the main linacs to precisely monitor the beam trajectory in the circular beam pipe of only 8 mm diameter. The PACMAN project aims to demonstrate the pre-alignment of the magnetic field of a main CLIC quadrupole with the electro-magnetic centre of a 15 GHz RF-BPM to the required sub-micron accuracy. This paper focuses on stretched-wire measurements of a CLIC Test Facility (CTF) cavity BPM, to locate its electrical centre. Details of two measurement methods are discussed: RF signal excitation of the wire and analysis of RF signal transfer through the slot-coupled waveguides of the cavity, using the stretched wire as a passive target. This contribution will present the theory behind these measurements, their electromagnetic analysis and first, preliminary experimental results.