Laser Wire and Beam Position Monitor tests

This subtask involved two main activities; Firstly the development and subsequent usage of high resolution beam position monitors (BPM) for the International Linear Collider (ILC) and Compact Linear Collider projects (CLIC); and secondly the development of a laser-wire (LW) transverse beam size measurement systems. This report describes the technical progress achieved at a large-scale test ILC compatible BPM system installed at the Accelerator Test Facility 2 (ATF2). The ATF2 is an energy-scaled demonstration system for the final focus systems required to deliver the particle beams to collision at the ILC and CLIC. The ATF2 cavity beam position monitor system is one of the largest of its kind and rivals systems used at free electron lasers. The ATF2 cavity beam position system has achieved a position resolutionof 250 nm (with signal attuenation) and 27 nm (without attenuation). The BPM system has been used routinely for lattice diagnostics, beam based alignment and wakefield measurements. Extensive experience has been gained in the operational usage of high resolution CBPMs in a realistic accelerator environment. Hardware development of cavity was conducted in the context of CLIC, where devices were designed, prototyped at the CTF3 facility at CERN. Similarly technical progress is reported for the laserwire system installed at ATF2, where micrometre beam sizes have been measured with uncertainties of less than 10%. The horizontal to vertical aspect ratio of low emittance electron beams is typically large and this causes a problem for laser focii. We developed a method to extract the electron beam size when the Rayleigh range of the laser focus is comparable to the horizontal beam size. This involved fitting using a full convolution of the laser photon and electron number densities. In parallel to the ATF2 LW, the PETRA3 laserwire has developed the use of fibre lasers for Compton scattering and the progress using fibre lasers is reported.