Research Of The Turn By Turn And Bunch By Bunch Beam Position Acquisition System Algorithm And Implementation For HIAF

After the beam is injected into the storage ring,there are magnetic field imperfections and mechanical misalignments in the synchrotrons;the beam injection angle is not at an ideal cut-in angle when it is injected into the storage ring;and other nonlinear components in the process of manufacturing,installation and operation the tiny deviations in the vacuum pipe,which causes the beam deviated from the ideal orbit when it is running at high speed in the vacuum pipe,and the beam oscillates in the lateral direction.It becomes very important to measure the lateral position of the beam in the vacuum pipe in real-time.Aiming at the phenomenon that the beam lateral position in the storage ring oscillates,the algorithm and implementation of the turn-byturn and bunch-by-bunch beam position measurement system in the synchrotron are studied in this research.The bunch-by-bunch beam position measurement system can quickly read the position information of a single beam bunch,providing accelerator physics researchers with more data on the behavior of macroscopic particles in the machine;the average beam position of multiple turns is provided to the closed-orbit system,a higher-precision beam position,giving beam commissioning personnel a convenient and quick "eye",observe the lateral position of the beam in the vacuum pipe in real-time,and provide powerful conditions for accelerator physics researchers to investigate the machine property and scientific experiments.At present,the beam position measurement(BPM)mainly uses the non-intercept detector plate to induce the beam signal,and according to the signal characteristics of the detector plate,the goal of the beam position measurement could be realized.The commonly used beam position detection system consists of a beam position monitor plate,front-end amplifier,and data acquisition electronics system.The front-end amplifier amplifies the beam current signal sensed by the pick-ups and transmits it to the data acquisition electronics system through a long-distance cable.Data acquisition electronics convert analog signals to digital signals and use advanced digital signal processing techniques and algorithms to convert detector plate signals into the beam position information.From the pick-ups to the data acquisition electronics,the key is to use existing technology to extract useful information from the raw detector waveform data.The main content of the bunch-by-bunch beam position acquisition system studied in this work is to obtain the beam position information of a single beam bunch and the beam position with higher precision multi-turn average values.In this work,two technical methods are applied to research the turn-by-turn and bunch-by-bunch BPM algorithm,one is the In-phase and Quadrature(IQ)demodulation method,and another is the Software Phase Lock Loop(SPLL)gated-controlled integral algorithm.Using the principle of IQ demodulation,the radio-frequency signal provided by the storage ring is used as the reference signal.The data from four BPM pick-ups are mixed with the reference signal separately,and then the mixed data is extracted by the CIC filters which decrease data rates down to 10 k Hz.The data from CIC filters could be used to calculate the relative amplitude of the beam current signal induced on each plate.The average position values of the beam could be calculated by using the amplitude of the four plates according to the formula of the different ratios.In the IQ demodulation algorithm,the most critical technique is the generation of the orthogonal data stream.In this work,the schemes of Hilbert transform orthogonal data stream and real-time acquisition of accelerator cyclotron frequency input DDS to generate orthogonal data stream are proposed respectively.The SPLL gate-controlled integral algorithm utilizes the sum data of the four BPM plates to generate a local oscillation(LO)signal which has the same frequency as the synchrotron and then generates the integral gate signal according to the phase lookup table that generates the LO signal.The widths of the integral gate could be adjusted within the synchrotron period.In the calculation,the data collected on each detector plate starts to be integrated when the integration gate signal is enabled.After the integration gate signal is disabled,the relative amplitude of the beam current signal on each plate is obtained.The obtained beam position in this method is the position value of the signal bunch passing through the current detector plate,ie.,the bunch-by-bunch beam position measurement.The turn-by-turn position value of each beam bunch could be a sequential sampling of the bunch-by-bunch data.In these two approaches,the sum of the relative amplitudes of the four plate signals can represent the relative current intensity in the storage ring.Two sets of beam position calculation algorithms run simultaneously in a single FPGA.After the algorithm is completed,validation tests are conditioned in the laboratory.The SPLL gated-controlled integral algorithm under laboratory conditions could realize the frequency-locking and phase-locking with a frequency jump of 20 k Hz.The position test results under laboratory conditions show that at the position sensitivity coefficient of 90 mm,the position measurement resolution of the turn-by-turn beam position is better than 3 μm,the bunch-by-bunch method is better than 6 μm,and the long-term position stability deviation of the position is less than 40 μm when the room temperature variation range is 4 °C @25 °C.Since the High Intensity Heavy-ion Accelerator Facility(HIAF)complex is still under construction,the beam position acquisition system studied in this research was first tested and verified at the Heavy Ion Research Facility in Lanzhou(HIRFL).When the beam testing condition is ready,the BPM plate signal amplified by the highimpedance front-end amplifier is mainly tested.Experimental tests verified the function of the SPLL,and the experimental results showed that the beam signal and the LO signal could be locked during acceleration.In the verification of the position measurement,the commercial product Libera Hadron is also connected for comparative testing,comparing the position values of the beam.The beam position measured by the IQ algorithm and the results measured by the Libera Hadron narrowband analysis algorithm is consistent in macroscopic period and microscopic details.In the comparison of the SUM value,the SUM value output by the Hilbert transform method was compared,the SUM values were oscillating,and the reason for the oscillations was discussed.The algorithm for generating the sum value of the quadrature data stream using DDS was tested,and the SUM values at this time did not oscillate,and the result was consistent with the Libera NBA algorithm.The position values measured in this research topic are compared with the results of the residual gas ionization profile detector running on HIRFL,which can be matched with each other.All the above test results show that the system can realize the beam position measurement in turn-by-turn and bunch-by-bunch methods,and can meet the actual use requirements.