Philip Burrows

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.

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 AT F interaction point.

Abstract:

The CLIC acceleration scheme, in which the RF power used to accelerate the main high energy beam is extracted from a second high intensity but low energy beam, places strict requirements on the phase stability of the power producing drive beam. To limit luminosity loss caused by energy jitter leading to emittance growth in the final focus to below 1%, 0.2 degrees of 12 GHz, or 50 fs, drive beam phase stability is needed. A low-latency phase feedforward correction with bandwidth above 17.5 MHz will be used to reduce the drive beam phase jitter to this level. The proposed scheme corrects the phase using fast electromagnetic kickers to vary the path length in a chicane prior to the drive beam power extraction. A prototype of this system has been installed at the CLIC test facility CTF3 to prove its feasibility. The latest results from the system are presented, demonstrating phase stabilisation in agreement with simulations given the beam conditions and power of the kicker amplifiers. Necessary improvements in the phase monitor performance and optics corrections made to remove the phase-energy dependence via R56 in order to achieve this level of stability are also discussed.

Abstract:

A low-latency, intra-train, beam feedback system utilising a cavity beam position monitor (BPM) has been developed and tested at the final focus of the Accelerator Test Facility (ATF2) at KEK. A low-Q cavity BPM was utilised with custom signal processing electronics, designed for low latency and optimal position resolution, to provide an input beam position signal to the feedback system. A custom stripline kicker and power amplifier, and a digital feedback board, were used to provide beam correction and feedback control, respectively. The system was 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 system has been used to demonstrate beam stabilisation to below the 75 nm level. Results of the latest beam tests, aimed at even higher performance, will be presented.