A full digital beam position and phase measurement signal processing algorithm based on FPGA designed for linear accelerator

A new digital beam position and phase measurement (BPM) system was designed for the ion-Linac (iLinac) accelerator in the High Intensity heavy ion Accelerator Facility (HIAF). The fundamental and the second harmonic signals are retrieved from the BPM electrodes to simultaneously calculate their respective beam positions and phases. All data acquisition and digital signal processing algorithm routines are performed in a field programmable gate array (FPGA). The position and phase information are obtained by using the in-phase and quadrature (IQ) demodulation method. A practical and straightforward method is used to generate the second harmonic reference signal for processing the second harmonics beam signal. The reconfigurable filters are integrated into the FPGA to allow the measurement of short beam pulse length. The laboratory test results show the achieved phase resolution is better than 0.2$^{\circ}$ and 0.03$^{\circ}$ when the input signal is -60 dBm and -45 dBm respectively. A position resolution better than 30 $\mu$m was achieved for an input power level of approximately -60 dBm, and it can reach 7 $\mu$m with the input power higher than -45 dBm. The entire execution time of the algorithm is accomplished within 3.4 $\mu$s, which provides a sufficient reaction time for the fast beam interlock signal to the machine protection system (MPS). The performance of this newly designed prototype BPM electronics was evaluated with the online proton beam.