Philip Burrows

Abstract:

A high-resolution, low-latency beam position monitor (BPM) system has been developed for use in feedback systems at particle accelerators and beamlines that operate with trains of particle bunches with bunch separations as low as several tens of nanoseconds, such as future linear electron-positron colliders and free-electron lasers. The system was tested with electron beams in the extraction line of the Accelerator Test Facility at the High Energy Accelerator Research Organization (KEK) in Japan. The fast analogue front-end signal processor is based on a single-stage RF down-mixer, with a measured latency of 15.6 ± 0.1 ns. The processor has been optimised, doubling the maximum operating beam intensity up to 1.6 nC, and the signal processing in the custom digital acquisition board has been upgraded in order to improve the resolution beyond the 300 nm level measured previously. The latest results, demonstrating a position resolution of order 150 nm with single-pass beam, will be presented.

Abstract:

A lowlatency feedback system has been designed and tested to achieve interbunch position stabilisation at the final focus of the Accelerator Test Facility (ATF2) at KEK. This system has now been enhanced through the use of position information from two cavity beam position monitors (BPMs) to enable beam stabilisation at a third, intermediate location where a witness BPM measures the correction. LowQ cavity BPMs were used, along with custom signal processing electronics designed for low latency and optimal position resolution. A custom stripline kicker, power amplifier and digital feedback board were used to provide beam correction and feedback control. The system was tested in singlepass, multibunch mode with the aim of providing interbunch beam stabilisation on electron bunches of charge ~1 nC separated in time by 280 ns. In 2015 a single BPM feedback system demonstrated beam stabilisation to below 75 nm. To date the two BPM input feedback system has demonstrated beam stabilisation to 83 ± 6 nm. This performance is limited by the current understanding of the cavity BPM resolution. Work will be described with the aim of improving this result.

Abstract:

As the design of the CLIC beam delivery system (BDS) evolves, tuning simulations must be performed on each of the proposed lattice designs to see which system achieves the highest luminosity in the most realistic manner. This work will focus on the tuning simulations performed on the so-called Traditional lattice design for the center-of-mass energy of 3 TeV. The lattice modifications required to target the most important aberrations and the latest tuning results will be presented.

Abstract:

Shadowgraphy is a technique widely used to diagnose objects or systems in various fields in physics and engineering. In shadowgraphy, an optical beam is deflected by the object and then the intensity modulation is captured on a screen placed some distance away. However, retrieving quantitative information from the shadowgrams themselves is a challenging task because of the non-linear nature of the process. Here, a novel method to retrieve quantitative information from shadowgrams, based on computational geometry, is presented for the first time. This process can also be applied to proton radiography for electric and magnetic field diagnosis in high-energy-density plasmas and has been benchmarked using a toroidal magnetic field as the object, among others. It is shown that the method can accurately retrieve quantitative parameters with error bars less than 10%, even when caustics are present. The method is also shown to be robust enough to process real experimental results with simple pre- and post-processing techniques. This adds a powerful new tool for research in various fields in engineering and physics for both techniques.

Abstract:

A custom 9-channel feedback controller has been developed for low-latency applications in beam-based stabilisation. Fast 14-bit ADCs and DACs are used for highresolution signal conversion and a Xilinx Virtex-5 FPGA is used for core high-bandwidth digital computation. The sampling, and fast digital logic, can be clocked in the range 200 to 400MHz, derived from an external or internal source. A custom data acquisition system, based around LabVIEW, has been developed for real-time control and monitoring at up to 460 kbps transfer rates, and is capable of writing and reading from EPICS data records. Details of the hardware, signal processing, and data acquisition will be presented. Two examples of applications will also be presented: a position and angle bunch-by-bunch feedback system using strip-line beam position monitors to stabilise intra-train positional jitter to below the micron level with a latency less than 154 ns; and a phase feedforward system using RF cavity-based phase monitors to stabilise the downstream rms phase jitter to below 50 fs with a total latency less than the 380 ns beam time-of-flight.