System Schematic Design And Error Analysis Of Beam Charge Monitor

The particle accelerator is an important experimental device in the field of high energy physics,and the beam monitor is also an integral part of the particle accelerator.The M(?)ller experiment being prepared by the Jefferson Laboratory in the United States has been proposed to carry out an ultra-precise measurement of the parity-violating left-right asymmetry in the M(?)ller scattering of longitudinally polarized 11GeV electrons off electrons in a liquid hydrogen target.In order to achieve this measurement accuracy,it is necessary to correct the effect of incident particles number on the measurement results in M(?)ller's experiment,we need to monitor the number of incident particles in real time.According to the requirement of M(?)ller experiment,the beam charge need to be measured with the relative precision of 10 parts per million per 1ms window.In order not to affect the motion of beam,we proposed a novel fully digital microwave processor based on a fast,3-4Gsps 10-bit digitizer.The principle of this measurement scheme is to measure the TM010 mode signal generated by the microwave cavity when beam passes through the cavity.It is known that the peak voltage of the TM010 mode harmonic signal is proportional to the amount of beam charge,by measuring the amplitude or power of this harmonic signal,we can obtain the beam charge information.The core issue of this paper is to achieve a high-precision measurement of RF signal power.This article proposed a RF direct measurement scheme based on a high speed ADC with 3-4 GSPS sampling rate and 10 bits ENOB.This article presents detailed descriptions of three types of noise effects on the measurement accuracy.By theoretical calculations and simulations we estimate that the system proposed can measure the power of a lOmW RF signal with a relative precision of 1.53ppm.In addition to the theoretical calculations and simulations,this article has completed the test work of the measurement accuracy of the data readout system based on the AD9656 chip,and has designed the system firmware and software.The experimental results show that the measurement accuracy of this system is basically consistent with the theoretical calculation results,which confirms the correctness of the system measurement accuracy estimation method in this paper.Moreover,it lays a solid foundation for the subsequent use of high-speed ADC to build a direct RF sampling system.