Beam Position and Beam Hopping Design for LEO Satellite Communications

The numbers of beam positions(BPs)and time slots for beam hopping(BH)dominate the latency of LEO satellite communications.Aiming at minimizing the number of BPs subject to a predefined requirement on the radius of BP,a low-complexity user density-based BP design scheme is proposed,where the original problem is decomposed into two subproblems,with the first one to find the sparsest user and the second one to determine the corresponding best BP.In particular,for the second subproblem,a user selection and smallest BP radius algorithm is proposed,where the nearby users are sequentially selected until the constraint of the given BP radius is no longer satisfied.These two subproblems are iteratively solved until all the users are selected.To further reduce the BP radius,a duplicated user removal algorithm is proposed to decrease the number of the users covered by two or more BPs.Aiming at minimizing the number of time slots subject to the no co-channel interference(CCI)constraint and the traffic demand constraint,a low-complexity CCI-free BH design scheme is proposed,where the BPs having difficulty in satisfying the constraints are considered to be illuminated in priory.Simulation results verify the effectiveness of the proposed schemes.

Diagnostic Method for Beam Position Monitor Based on Clustering by Fast Search and Find of Density Peaks

Beam position monitors(BPMs)are important to monitor the beam moving steadily.Keeping the beam's normal motion is an important mission for Shanghai Synchrotron Radiation Facility.Effective diagnostic analysis is an important way to accomplish this task.This paper develops a new method based on clustering analysis to diagnose the healthy of BPMs with basic running data,i.e.,the β oscillation of X and Y directions and noise data.The analysis results showed that all beam position monitors(140 BPMs)can be classified into three groups:normal group,worse performance group,and fault group,respectively.In addition,the abnormal BPMs(including worse performance)could be marked.The new method showed its ability to handle faulty BPMs and it could instruct daily maintenance.On the other hand,it will be a useful supplement for data analysis in accelerator physics.

Electro-mechanical offset measurements of beam position monitors

Purpose The absolute beam position measurement in the booster and storage ring of the high energy photon source(HEPS)requires the offset between the electrical and mechanical centers of the beam position monitor(BPM).Method Traditionally,an RF signal is sent to an antenna or stretched wire aligned with the vacuum chamber,and the signal at each electrode is measured.Conversely,a replacement method using a vector network analyzer,which was proposed by Lambertson,does not involve mechanical alignment and can be used for electrical offset determination.Results and conclusions The electro-mechanical offsets of booster BPMs of the HEPS were measured using the Lambertson method.The result shows good agreement with the stretched wire method within a 30μm error.

Capacitive beam position monitors for the low-β beam of the Chinese ADS proton linac

Beam Position Monitors（BPMs） for the low-β beam of the Chinese Accelerator Driven Subcritical system（CADS） Proton linac are of the capacitive pick-up type.They provide higher output signals than that of the inductive type.This paper will describe the design and tests of the capacitive BPM system for the low-β proton linac,including the pick-ups,the test bench and the read-out electronics.The tests done with an actual proton beam show a good agreement between the measurements and the simulations in the time domain.

Design and simulation of a beam position monitor for the high current proton linac

In this paper, the 2-D electrostatic field software, POISSON, is used to calculate the characteristic impedance of a BPM （beam position monitor） for a high current proton linac. Furthermore, the time-domain 3-D module of MAFIA with a beam microbunch at a varying offset from the axis is used to compute the induced voltage on the electrodes as a function of time. Finally, the effect of low β beams on the induced voltage, the sensitivity and the signal dynamic range of the BPM are discussed.

A new measurement method for electrode gain in an orthogonally symmetric beam position monitor

The new beam position monitor（BPM） system of the injector at the upgrade project of the Hefei Light Source（HLS II） has 19 stripline beam position monitors. Most consist of four orthogonally symmetric stripline electrodes. Differences in electronic gain and mismachining tolerance can cause changes in the beam response of the BPM electrodes. This variation will couple the two measured horizontal positions, resulting in measuring error. To alleviate this effect, a new technique to measure the relative response of the four electrodes has been developed. It is independent of the beam charge, and the related coefficient can be calculated theoretically. The effect of electrode coupling on this technique is analyzed. The calibration data is used to fit the gain for all 19 injector beam position monitors. The results show the standard deviation of the distribution of measured gains is about 5%.

Automatic test system development for digital beam position monitor of HEPS and BEPCII

Purpose Hundreds of digital beam position monitor processors(DBPM)are required to be produced during the construction of projects such as High Energy Photon Source(HEPS)and the upgrade project of the Beijing Electron Positron Collider(BEPCII),which brings great challenges to the test work.In order to achieve accurate,fast,and complete mass production tests of DBPMs,an automatic test system(ATS)has been developed in this article.Methods According to the test items of DBPM,the standardized testing softwareflow is designed based on virtual instru-ment program control technology and experimental physics and industrial control system(EPICS),which realize automatic adjustment of test parameters and automatic acquisition of test result data.Results and conclusions The ATS can realize one-button testing of channel coefficients,channel linearity,attenuator linearity,beam current dependence(BCD)and sampling signal-to-noise ratio(SNR),and generate test reports.The total test time is less than 3 minutes,which is significantly more efficient compared to manual testing.More than 90 BEPCII DBPMs has been tested by this ATS in the lab.The test results proved that such a system could automatically recognize defective products and satisfy the requirements of mass testing.

Novel cued search strategy based on information gain for phased array radar

A search strategy based on the maximal information gain principle is presented for the cued search of phased array radars. First, the method for the determination of the cued search region, arrangement of beam positions, and the calculation of the prior probability distribution of each beam position is discussed. And then, two search algorithms based on information gain are proposed using Shannon entropy and Kullback-Leibler entropy, respectively. With the proposed strategy, the information gain of each beam position is predicted before the radar detection, and the observation is made in the beam position with the maximal information gain. Compared with the conventional method of sequential search and confirm search, simulation results show that the proposed search strategy can distinctly improve the search performance and save radar time resources with the same given detection probability.

激光扫描定位仪的原理与设计

文章介绍激光扫描定位仪的原理以及其信号处理方法。该仪器利用压电陶瓷扫描器PZTA产生激光扫描线，二象限光电管接收激光，光电流引入单片机处理，再数字显示偏差值，定位长度大于3m，灵敏度优于25μm，在线性范围为±1．5mm，非线性误差0．6％。

A GEO Satellite Position and Beam Features Estimation Method Based on Beam Edge Positions

Constrained by orbital configuration and spectrum sharing,non-geostationary orbit(NGEO)satellites may be interfered when they are in the beam range of geostationary orbit(GEO)satellite.However,it is difficult for NGEO operators to determine the signal source.Herein,we propose a method to locate the GEO signal source and estimate beam features,including beam pointing azimuth,elevation,and beamwidth,by the beam edge positions.We transform this estimation problem into two optimization problems by minimizing the estimation error,and solve both of them through a multi-variable joint iteration method with acceptable computation complexity.Numerical results show that when NGEO satellites pass through the beam twice,the longitude estimation error is about 0.01 degree,and the estimation results will be more and more accurate as the number of passing times increases.Besides,the proposed method is also effective when there are kilometer-level errors in beam edge positions.

基于轮廓防错的侧梁组装工装设计

针对侧梁组装过程中不合格品检出率低、定位不准确的问题,在分析了工件的结构特点和组装工艺的基础上,以工件外形轮廓定位,提出了基于轮廓防错的全封闭式结构的工装设计方案,创新设计了定位器,使定位更加准确,并能在组装过程中有效防错,降低了组装难度,提高了产品制造的可靠性和质量的稳定性。

Recent Developments of Beam Diagnostics

The paper introduces some of the recent developments in beam diagnostics,which include the beam position measurement techniques with sub-micrometer resolution,the beam size measurement techniques with sub-micrometer resolution,and the bunch length measurement techniques with sub-picosecond resolution.The cavity beam position monitor and the digital BPM signal processing technique are introduced for the beam position measurement techniques. The laser wire beam profile monitor,and the optical transition radiation/optical diffraction radiation beam size monitor are introduced for the beam size measurement techniques.The spectral techniques of coherent radiation,the transverse deflecting cavity,the rf zero-phasing technique,and the electro-optic techniques are introduced for the bunch length measurement techniques.

Research and Measurement of Synchrotron Radiation System for HLS

The paper introduces the synchrotron radiation system for Hefei Light Source (HLS),which includes the streak camera system,the bunch length system using photoelectric method,the beam profile measurement system,and the photon beam position measurement system.The bunch length and bunch lengthening were measured using the streak camera system and the photoelectric method.The beam profile measurement system was used to observe the suppression effects of sextupole on beam transverse instability and the feedback effects of the transverse bunch-by-bunch feedback system.The photon beam position measurement system used two wire-type monitors and the logarithmic signal processor,which was used to detect the beam motions.

Effect of Laser Welding on Properties of Dissimilar Joint of Al-Mg-Si and Al-Mn Aluminum Alloys

This study discusses the welding properties for the components of an aluminum-alloy ultra-high vacuum chamber and beam position monitor （BPM）.The welding parameters include the modes of laser output （pulsed wave and continuous wave）,welding speed,shield gas flow,welding bead structure,and focusing distance.The results showed that the welding defect rate of the pulsed wave type was larger than that of the continuous wave type.The crack in the welding bead reduced with decreasing welding speed.The fusion penetration of the welding bead was higher when the focusing distance was long enough to deepen into the welding material.Weld morphology during the experimental process revealed the proper flow of shield gas.The adaptability design of the welding bead structure in the preceding processes had more effect on overall welding structure and morphology.

Conditioning of BPM pickup signals for operations of the Duke storage ring with a wide range of single-bunch current

The Duke storage ring is a dedicated driver for the storage ring based oscillator free-electron lasers（FELs）, and the High Intensity Gamma-ray Source（HIGS）. It is operated with a beam current ranging from about1 mA to 100 mA per bunch for various operations and accelerator physics studies. High performance operations of the FEL and γ-ray source require a stable electron beam orbit, which has been realized by the global orbit feedback system. As a critical part of the orbit feedback system, the electron beam position monitors（BPMs） are required to be able to precisely measure the electron beam orbit in a wide range of the single-bunch current. However, the high peak voltage of the BPM pickups associated with high single-bunch current degrades the performance of the BPM electronics, and can potentially damage the BPM electronics. A signal conditioning method using low pass filters is developed to reduce the peak voltage to protect the BPM electronics, and to make the BPMs capable of working with a wide range of single-bunch current. Simulations and electron beam based tests are performed. The results show that the Duke storage ring BPM system is capable of providing precise orbit measurements to ensure highly stable FEL and HIGS operations.

Preliminary application of turn-by-turn data analysis to the SSRF storage ring

There is growing interest in utilizing the beam position monitor turn-by-turn（TBT） data to debug accelerators. TBT data can be used to determine the linear optics,coupled optics and nonlinear behaviors of the storage ring lattice. This is not only a useful complement to other methods of determining the linear optics such as LOCO,but also provides a possibility to uncover more hidden phenomena. In this paper,a preliminary application of a β function measurement to the SSRF storage ring is presented.

Design and simulation of cavity BPM for BEPCII

Background In the linac of Beijing Electron Positron Collider II(BEPCII),the resolution of existing BPMs is several hundred microns.But the requirement of transverse position resolution of BPM for future top-up injection needs to be more precise.Purpose This paper is mainly concerned about the design and simulation of the cavity beam position monitor(CBPM)for BEPCII linac and free electron laser(FEL).The requirement of beam transverse position resolution for linac is several microns,even a few nanometers for FEL.Methods When the beam bunch goes through the CBPM,it can excite different electromagnetic field modes in resonator.In these modes,TM_(110) is the most sensitive to beam transverse position offset.The design of CBPM is aim to analyze the relationship between TM_(110) and beam transverse position by CST Studio and Ansys HFSS.Conclusion In this research,we design a pair of rectangular slots for position cavity to revise the direction of electromagnetic field.The simulation result of theoretical resolution is able to reach 15 nm@1nC with the operating frequency 2500 MHz.It is obviously that CBPM has more excellent resolution than all of operating BPM in BEPCII.Meanwhile,the research of CBPM improves the application of beam detection technology in BEPCII and accumulates technology for future design of HEPS and FEL.The mechanical design of the prototype is being fabricated.