For particle accelerators to operate and to deliver particle beams to their intended targets, a device called a beam position monitor (BPM) serves as a basic diagnostic tool. The electrical signal amplitudes induced by the beam on the BPM’s pickup electrodes (PUEs) are used to determine the beam location. This procedure often requires lengthy computations for good accuracy, especially when the beam is far off-center.

Publishing its work in Review of Scientific Instruments, a research team presents a new algorithm that can relay beam position information quickly and accurately using data from beam position monitors. The algorithm takes advantage of the symmetry of the cylindrical shape that many accelerators and beam transports have, and uses signals from four PUEs.

The one-dimensional algorithm works by normalizing the two-dimensional signal differences into a single vector “Q” in the direction of the beam. The position of the beam then becomes a simpler, nonlinear function of the magnitude of Q, which is projected on axes to obtain the beam’s coordinates. This new solution they found is strictly valid in the limit of small PUEs and fully relativistic beams.

The approach yielded only slight deviations when applied to simulations of realistic BPMs with finite width PUEs, as well as simulations for nonrelativistic beams. These deviations are further mitigated with simple correction terms. Based on this approach, the researchers developed a BPM readout circuit based on Field Programmable Gate Arrays, allowing bunch intervals of 70 nanoseconds. Tests with BPM data from the Cornell Preinjector were successful.

Source: “Fast readout algorithm for cylindrical beam position monitors providing good accuracy for particle bunches with large offsets,” by P. Thieberger, D. Gassner, R. Hulsart, R. Michnoff, T. Miller, M. Minty, Z. Sorrell, and A. Bartnik, Review of Scientific Instruments (2018). The article can be accessed at