A Fully Digital Beam Position and Phase Measurement Electronics for the Proton LINAC in ADS

The beam measurement is essential for an accelerator. In the proton LINAC in China Accelerator Driven Sub-critical system (ADS), a high resolution measurement of beam position and phase is required within one single system. To meet the requirement, this beam position and phase measurement (BPPM) electronics is designed based on a direct RF under-sampling technique, which simplifies both the analog and digital processing circuits. The signals received from the LINAC are narrow pulses with a repetition frequency of 162.5 MHz and a dynamic range more than 40 dB. After analog manipulation, the input RF signals are directly converted to In-phase and Quadrature-phase (IQ) streams through under-sampling based on the high-speed high-resolution Analog-to-Digital conversion technique. All signal processing is integrated in one single FPGA, in which real-time beam position, phase and current can be obtained. A series of simulations and tests have been conducted to evaluate the performance. Initial test results indicate that this system achieves a position resolution better than 20 um and a phase resolution better than 0.1 degree over a 40 dB dynamic range with the bandwidth of 780 kHz, which is well beyond the application requirements.