Earch Of The Beam Position And Phase Measurement For The Proton LINAC In ADS

In the application of the nuclear energy, the safety and nuclear waste problem become more and more important. The Accelerator Driven Sub-critical System （ADS） is capable of transmuting radioactive nuclear wastes and meanwhile producing energy in a clean and safe way, and thus it is now a very important worldwide research domain. As a key part of ADS, a high intensity proton LINAC is required to produce high power proton beams. To guarantee a high beam quality, good beam diagnostics is indispensable. This thesis studies a fully digital beam measurement method, and implements a prototype of high-resolution beam position and phase measurement （BPPM） electronics for the proton LINAC in China ADS.This BPPM electronics measures both beam position and phase with four induction signals from the BPM detectors and a MO signal （162.5MHz sine wave） as a phase reference. The induction signals are162.5MHz periodic narrow pulses, and the amplitude would vary from0.01V to1V, which corresponds to an input range of around-44～-4dBm （considering the attenuation of the cables, etc.）. And the position and phase resolutions are required to be better than0.2mm and±0.5degree in the input amplitude range of-38～-4dBm. In order to minimize the interference from RF （Radio Frequency） system, we focus on the design based on the processing of the second harmonic frequency component_325MHz of the signal. Meanwhile a prototype based on the fundamental frequency component （162.5MHz） is also designed for comparison.Traditional beam position and phase measurement methods are based on analog signal manipulation. The system performance is easily deteriorated by the noise, non-linearity and mismatches of the analog circuits. With the development of A/D conversion and digital signal processing techniques, the modern technique is to digitize the signal at the front end, namely fully digital beam measurement. The mainstream digital method is the digital IQ demodulation, and it greatly reduces the complexity of the analog circuits; however, quite complex DSP （Digital Signal Processing） algorithms are required. This BPPM electronics is designed based on a new method--RF signal IQ undersampling （RFIQUS） technique, which simplifies both the analog circuits and the DSP algorithms. Both beam position and phase are implemented within one single system, which simplifies the system architecture and enhances the integrity.For an off-axis beam, the signal phases from individual electrodes would differ from those for a centered beam by a few degrees, while the phase of a summed signal （from all the BPM electrodes） remains the same within the computation error （0.1-0.2degree）. Simulation of the signals with DSP algorithms for beam phase measurement is also studied in this thesis. So this system measures the beam phase working with the summed signal.After hardware implementation, we conducted a series of tests in the laboratory and the test results indicate that the performance of the two systems （processing the second harmonic and the fundamental frequency components of the signal） is better than the application requirements.In chapter1, we first introduce the basic concepts of the beam measurement; and present the development of ADS; at last conclude the necessity of high performance beam position and phase measurement.In chapter2, the techniques of beam position and phase measurement are discussed, such as beam detectors and signal processing electronics. Through the comparison of Logarithmic ratio, Amplitude-to-Phase Conversion （AM/PM） and Δ/Σ, the final signal processing method is selected. Then we review the beam measurement methods. Several typical beam diagnostic systems of accelerators are presented, as a technique background for the design of this BPPM electronics.Chapter3details the characteristics of the input signals and the requirement on the beam position and phase measurement in the proton LINAC of ADS. Based on the discussion in chapter2, the BPPM systems employ a fully digital-beam measurement method based on the RFIQUS technique, and the feasibility of this technique is verified by simulations based on the Matlab platform. Based on this method, several design issues are analyzed, and the whole system structure is introduced.From chapter5to chapter6, we introduce the designs and implementations of the two electronics prototypes:one is based on the processing of the second harmonic frequency component, and the other is based on the processing of the fundamental frequency component. We present the design of the analog front-end circuits, and the high-speed high-resolution A/D Conversion circuits; to guarantee the signal integrity, PCB placing and routing are carefully considered; we also analyze the power supply and thermal dissipation issues. Chapter5details the DSP algorithms and data transfer interface logic design.To evaluate the system performance, a series of tests were conducted. The test results are presented in chapter6, which indicate that:over the input amplitude dynamic range of-44～-4dBm （larger than the required amplitude range）, the measurement resolutions of beam phase（phase difference between the summed signal and MO signal）, position and current of the first system （second harmonic frequency component processing） are better than0.03degree,5um and0.02%; and those of the second system （the fundamental frequency component processing） are better than0.03degree,3um and0.012%. These results are well beyond the application requirements. In addition, the dynamic range of the two system is as large as60dB （corresponding to-60-0dBm）, and over this range the measurement resolutions are better than0.14degree,30um and0.1%for the first system, and0.15degree,15um and0.06%for the second system.In chapter7, we give a summary of the work and the outlook for the future work.