Philip Burrows

Abstract:

One of the goals of the CLIC Test Facility (CTF3) [1] at CERN is to demonstrate the feasibility of the CLIC [2] Drive Beam recombination, which takes place in the Drive Beam Recombination Complex (DBRC). The tight geometry of the DBRC together with its strong optics and the high energy spread of the beam require a careful control of the beam size along the different sections of the DBRC [3, 4]. One of the main contribution to beam size is the dispersion. If uncontrolled, dispersion leads to fast increase of the beam size, hence it may affect the beam current stability of the combined beam. A tool has been implemented at CTF3 to measure and correct dispersion during and after the setup of the machine. Dispersion Free Steering (DFS) has been applied in the upstream Drive Beam LINAC, while Dispersion Target Steering (DTS) has been used in the rings of the DBRC. In the LINAC the weak optics and the wide dynamic aperture of the beamline allow a straightforward correction. In the DBRC the aperture is tighter, and the strong optics produce non-linear dispersion which one needs to take into account. A general overview of current status and future plans in controlling dispersion at CTF3 will be presented.

Abstract:

The CLIC design relies on the two-beam acceleration principle, i.e. the energy transfer from the so called drive beam to the main colliding beams. At the CLIC Test Facility (CTF3) at CERN the feasibility of this principle is being tested in terms of performance and achievable specifications. The high-current drive beam is generated by recombining its parts in a delay loop and a combiner ring. Preserving the drive beam emittance during the recombination process is crucial to ensure beam-current and power production stability. Present theoretical and experimental studies show that non-linear energy dependence of the transverse optics heavily spoils the quality of the recombined beam. Conventionally these effects are cured by means of non-linear corrections using sextupoles. In this work we propose a mitigation of these effects by optimising the linear lattice, leading to a more robust and easy to operate drive beam recombination complex. The latest results are presented.

Abstract:

The Compact Linear Collider (CLIC) project is exploring the possibility of constructing a multi-TeV linear electron-positron collider for high-energy frontier physics studies beyond the LHC era. The CLIC concept is based on high-gradient normal-conducting accelerating structures operating at X-band (12 GHz) frequency. We present the status of development, prototyping and testing of structures for operating at gradients of 100 MV/m and beyond. We report on high-power tests of these structures using the "XBOX" test facilities at CERN and summarize experience with operation at high-gradients. We give an overview of developments for application of the X-band technology to more compact accelerators for use e.g. as X-ray FELs and in medicine.

Abstract:

A low-latency, sub-micron resolution stripline beam position monitoring (BPM) system has been developed and tested with beam at the KEK Accelerator Test Facility (ATF2), where it has been used to drive a beam stabilisation system. The fast analogue front-end signal processor is based on a single-stage radio-frequency down-mixer, with a measured latency of 16 ns and a demonstrated single-pass beam position resolution of below 300 nm using a beam with a bunch charge of approximately 1 nC. The BPM position data are digitised on a digital feedback board which is used to drive a pair of kickers local to the BPMs and nominally orthogonal in phase in closed-loop feedback mode, thus achieving both beam position and angle stabilisation. We report the reduction in jitter as measured at a witness stripline BPM located 30 metres downstream of the feedback system and its propagation to the ATF interaction point.

Abstract:

A system of three low-Q cavity beam position monitors (BPMs), installed in the interaction point (IP) region of the Accelerator Test Facility (ATF2) at KEK, has been designed and optimised for nanometre-level beam position resolution. The BPMs have been used to provide an input to a low-latency, intra-train beam position feedback system consisting of a digital feedback board and a custom stripline kicker with power amplifier. The feedback system has been deployed in single-pass, multi-bunch mode with the aim of demonstrating intra-train beam stabilisation on electron bunches of charge ~1 nC separated in time by c. 220 ns. The BPMs have a demonstrated resolution of below 50 nm on using the raw measured vertical positions at the three BPMs, and has been used to stabilise the beam to below the 75 nm level. Further studies have shown that the BPM resolution can be improved to around 10 nm on making use of quadrature-phase signals and the results of the latest beam tests will be presented.