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.

Alignment of beam position monitors in cryomodule of CADS injector Ⅱ

Significant temperature difference(300-77 K or even 4 K) can cause large deformations and displacements of the beam position monitors(BPMs),which affect BPMs measurement resolution or even cause their malfunction in cryogenic situations.In this paper,to check the offset from the mechanical to electrical center in low temperature(77 K),Fourier's law and finite element method are used to simulate cryo-deformation.Laser tracker and micro-alignment telescope are employed in combined BPM calibration,installation and monitoring.The calibration error is<0.02 mm,and the installation and monitoring precision are 0.06 mm and 0.01 mm,respectively.The monitored cryo-deformation agrees well with the simulation results.These indicate that the combined alignment can improve performance of the BPM system.All these guaranteed the success of running the 9.55 MeV@2.14 mA cw protons.

Effects of laser beam divergence angle on airborne LIDAR positioning errors

The influence of laser beam divergence angle on the positioning accuracy of scanning airborne light detection and ranging （LIDAR） is analyzed and simulated. Based on the data process and positioning principle of airborne LIDAR, the errors from pulse broadening induced by laser beam di vergence angle are modeled and qualitatively analyzed for different terrain surfaces. Simulated results of positioning errors and suggestions to reduce them are given for the flat surface, the downhill of slope surface, and the uphill surface.

Strip line beam position monitor for HLS LINAC

The parameters of beam transverse positions at HLS 200 MeV LINAC are very important to injection ef-ficiency. We have designed a new non-interceptive strip line beam position monitor (BPM) as a substitution for the original interceptive fluorescent target. This paper gives out the theoretical analysis and bench test result of the strip line BPM. The BPM has a characteristic impedance of (50±5)?, a reflection coefficient of less than –4 dB, a band-width of 400 MHz, a coupling coefficient of less than -15 dB, and a sensitivity of 1.16 dB/mm. Additionally, the strip line BPM has a good linearity.

Development of photon beam position feedback system based on two PBPMs at HLS

In this paper,in order to stabilize the position and angle of the light source point,a new photon beam position feedback system based on the Photon Beam Position Monitors was developed on Hefei Light Source,and used to correct the position drift and angle variation of the light source at the same time.On introducing the feedback principle,the transfer function matrix is calibrated,indicating that the new system is workable and effective.

Beam position monitors as precise phase pickups for beam energy measurement at the Compact Pulsed Hadron Source

The 13-MeV proton linac of the Compact Pulsed Hadron Source(CPHS) at Tsinghua University, China,is composed of a 50-keV electron cyclotron resonance proton source, a 3-MeV four-vane-type radio-frequency quadrupole(RFQ) accelerator, and a drift tube linac(DTL). Precise measurement of the beam energies at the exit of the RFQ and the DTL is critical for DTL commissioning. Two button-type beam position monitors(BPMs) installed downstream of the RFQ are used to perform the measurement using a time-of-flight method. The effects of several factors on phase measurement accuracy are analyzed. The phase measurement accuracy of the BPMs at CPHS is better than ± 1.03° at 325 MHz after corrections,corresponding to an energy measurement error of± 0.07%. The beam energy measured at the exit of the RFQ is 2.994 ± 0.0022 MeV,which is consistent with the design value.

Design and measurement of signal processing system for cavity beam position monitor

In this paper,in order to achieve the output signal processing of cavity beam position monitor(CBPM),we develop a digital intermediate frequency receiver architecture based signal processing system,which consists of radio frequency(RF) front end and high speed data acquisition board.The beam position resolution in the CBPM signal processing system is superior to 1μm.Two signal processing algorithms,fast Fourier transform(FFT) and digital down converter(DDC),are evaluated offline using MATLAB platform,and both can be used to achieve,the CW input signal,position resolutions of 0.31μm and 0.10μm at -16 dBm.The DDC algorithm for its good compatibility is downloaded into the FPGA to realize online measurement,reaching the position resolution of 0.49μm due to truncation error.The whole system works well and the performance meets design target.

A beam position measurement system of fully digital signal processing at SSRF

This fully digital beam position measurement instrument is designed for beam position monitoring and machine research in Shanghai Synchrotron Radiation Facility. The signals received from four position-sensitive detectors are narrow pulses with a repetition rate up to 499.654 MHz and a pulse width of around 100 ps, and their dynamic range could vary over more than 40 dB in machine research. By the employment of the under-sampling technique based on high-speed high-resolution A/D conversion, all the processing procedure is performed fully by the digital signal processing algorithms integrated in one single Field Programmable Gate Array. This system functions well in the laboratory and commissioning tests, demonstrating a position resolution (at the turn by turn rate of 694 kHz) better than 7 μm over the input amplitude range of -40 dBm to 10 dBm which is well beyond the requirement.

A Prototype of beam position and phase measurement electronics for the LINAC in ADS

This article presents a prototype of beam position and phase measurement(BPPM)electronics designed for the LINAC in China Accelerator Driven Sub-critical system(ADS).The signals received from the Beam Position Monitor(BPM)detectors are narrow pulses with a repetition frequency of 162.5 MHz and a dynamic range more than40 dB.Based on the high-speed high-resolution Analog-to-Digital conversion technique,the input RF signals are directly converted to In-phase and Quadrature-phase(IQ)streams through under-sampling,which simplifies both the analog and digital processing circuits.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 prototype achieves a phase resolution better than 0.1 degree and a position resolution better than 20μm over a 40 dB dynamic range with the bandwidth of 780 kHz,which is well beyond the application requirements.

Development of a PSD-based photon beam position measurement system

As an important part of the beam diagnostic system, the synchrotron light beam position measurement has a very high value in the high quality and high stability light source applied research. A new photon beam position monitor based on position-sensitive detector (PSD) has been developed to measure the photon beam position in vertical and horizontal directions at the same time at HLS (Hefei Light Source). The new PBPM based on the PSD has fast response speed, high sensitivity and wide dynamic range. This PBPM system also includes the C4674 signal processing circuit, NI USB-9215 data acquisition device and the LABVIEW data acquisition program. This PBPM system has been calibrated vertically and horizontally on-line, and then has been applied in the beam line B3EA of HLS to measure the position of the synchrotron light. As the results shown, the resolution of the system is better than 3 mm.

Beam position monitor troubleshooting by using principal component analysis in Shanghai Synchrotron Radiation Facility

Beam position monitors(BPMs)have been widely used in all kinds of measurement systems,feedback systems and other areas in particle accelerator field these days.The malfunction of a single BPM can cause serious consequences such as the failure of the orbit feedback and the transverse feedback.A troubleshooting has been made to prevent the defective BPMs from affecting the accuracy and stability of the storage ring in Shanghai Synchrotron Radiation Facility(SSRF).Different types of malfunctions have been successfully identified by using the idea of principal component analysis(PCA).

Research into the sampling methods of digital beam position measurement

A fully digital beam position monitoring system(DBPM) has been designed for SSRF(Shanghai Synchrotron Radiation Facility). As analog-to-digital converter(ADC) is a crucial part in the DBPM system, the sampling methods should be studied to achieve optimum performance. Different sampling modes were used and compared through tests. Long term variation among four sampling channels, which would introduce errors in beam position measurement, is investigated. An interleaved distribution scheme was designed to address this issue. To evaluate the sampling methods, in-beam tests were conducted in SSRF. Test results indicate that with proper sampling methods, a turn-by-turn(TBT) position resolution better than 1 μm is achieved, and the slow-acquisition(SA) position resolution is improved from 4.28 μm to 0.17 μm.

AN EXISTENCE THEOREM OF POSITIVE SOLUTIONS FOR ELASTIC BEAM EQUATION WITH BOTH FIXED END-POINTS

By using the degree theory on cone an existence theorem of positive solution for a class of fourth-order two-point BVP's is obtained. This class of BVP's usually describes the deformation of the elastic beam with both fixed end-points.

光学体表监测系统Catalyst HD的cPosition与cMotion功能在乳腺癌调强放疗中的应用

目的探究表面引导放射治疗(Surface Guided Radiation Therapy,SGRT)中辅助摆位功能cPosition与治疗实时监控功能cMotion在乳腺癌保乳术患者调强放疗中的影响。方法治疗前使用体表标记线摆位,接着使用cPosition进行辅助摆位,最后使用锥形束CT(Cone Beam CT,CBCT)进行体位验证。分别记录两种摆位方式摆位后的床值及CBCT校准后的体位误差数据;进行Pearson相关与样本t检验分析,观察cMotion过程中患者的位移误差并分析。结果体表标记线摆位与cPosition辅助摆位在前后(Anterior Posterior,AP)、上下(Superior-Inferior,SI)、左右(Left Right,LR)、旋转、翻转和俯仰(Pitch)方向的摆位误差t值分别为-3.438、-4.895、-3.473、-1.811、-3.608和4.273,前五项均P<0.05。CBCT校正与Catalyst HD中cPosition校正功能的Pearson相关分析中AP、SI、LR方向相关性均表现为极高度相关,Pitch方向表现为低度相关。结论使用c Position校正在AP、SI、LR、Pitch 4个方向上明显优于应用标记线摆位并且Catalyst HD中cPosition与CBCT校正存在很高的一致性,在一定程度上缩减CBCT的使用次数进而减少患者的辐射剂量;在cMotion中可以根据患者的呼吸运动及不自主的移动进行束流控制,保证治疗过程中的治疗精度。

Positive solutions of nonlinear elastic beam equations with a fixed end and a movable end

The existence of n positive solutions is studied for a class of fourth-order elastic beam equations where one end is fixed and other end is movable. Here, n is an arbitrary natural number. Our results show that the class of equations may have n positive solutions provided the “heights” of the nonlinear term are appropriate on some bounded sets.

Underwater Terrain Positioning Method Based on Least Squares Estimation for AUV

To achieve accurate positioning of autonomous underwater vehicles, an appropriate underwater terrain database storage format for underwater terrain-matching positioning is established using multi-beam data as underwater terrainmatching data. An underwater terrain interpolation error compensation method based on fractional Brownian motion is proposed for defects of normal terrain interpolation, and an underwater terrain-matching positioning method based on least squares estimation（LSE） is proposed for correlation analysis of topographic features. The Fisher method is introduced as a secondary criterion for pseudo localization appearing in a topographic features flat area, effectively reducing the impact of pseudo positioning points on matching accuracy and improving the positioning accuracy of terrain flat areas. Simulation experiments based on electronic chart and multi-beam sea trial data show that drift errors of an inertial navigation system can be corrected effectively using the proposed method. The positioning accuracy and practicality are high, satisfying the requirement of underwater accurate positioning.

Existence and multiplicity of positive solutions for an elastic beam equation

This paper investigates the boundary value problem for elastic beam equation of the formu″″（t） q（t）f（t, u（t）,u′（t）,u″（t）,u′″（t））, 0〈t〈1,with the boundary conditionsu=（0）=u′（1）=u″（0）=u′″（1）=0.The boundary conditions describe the deformation of an elastic beam simply supported at left and clamped at right by sliding clamps. By using Leray-Schauder nonlinear alternate, Leray-Schauder fixed point theorem and a fixed point theorem due to Avery and Peterson, we establish some results on the existence and multiplicity of positive solutions to the boundary value problem. Our results extend and improve some recent work in the literature.

Experimental study of delayed positive feedback control for a flexible beam

Recently, some researches indicate that positive feedback can benefit the control if appropriate time delay is intentionally introduced into control system. However, most work is theoretical one but few are experimental. This paper presents theoretical and experimental studies of delayed positive feedback control technique using a flexible beam as research object. The positive feedback weighting coefficient is designed by using the optimal control method. The available time delay is determined by analyzing the maximal real part of characteristic roots of the system. A DSP-based experiment system is introduced. Simulation and experimental results indicate that the delayed positive feedback control may effectively reduce the beam vibration if time delay is appropriately selected.

Position Verification of the RADPOS 4-D <i>In-Vivo</i>Dosimetry System

The accuracy of the position measurements obtained by the radiation positioning system (RADPOS) was evaluated under static and dynamic conditions. In the static verifications, the RADPOS was fixed to the treatment couch in a photon treatment room and a proton treatment room, and was translocated with the treatment couch in x, y and z directions. Because the presence of magnetic and/or electrically conductive materials can cause a systematic shift in the measured position by distorting the RADPOS transmitted field, the effect of metals on the performance of the positioning system was also investigated. Dynamic verification was performed using the couch drive and a dynamic anthropomorphic thorax phantom. We thus confirmed the utility of RADPOS as a position sensor to perform in vivo dosimetry.

可见光波段多路激光合束及闭环校正技术研究

为了实现可见光波段多路不同波长激光的周期性闭环校正,设计了一种具有光束指向和位置偏差独立监测与调节的激光合束系统。首先,根据系统的应用需求,提出了合束系统的设计指标与整体合束方案。然后,在合束方案的基础上,建立了合束系统的光束控制模型,并通过数值仿真得到了合束系统光束控制的解算方法。闭环合束系统通过光束指向和位置监测装置分别实现合束激光指向偏差与位置偏差的独立监测,并根据监测结果进行光束调节装置控制量的解算;进而通过两维摆镜和一维平移台分别实现光束指向和位置偏差的独立高效调节。最后,采用两路不同波长的激光束,配合光束监测与调节装置,搭建了闭环合束模拟实验平台,对周期性闭环合束系统的合束效果进行了验证。实验结果表明:在长时间的工作过程中,两路激光均实现了与基准光路的精密合束,合束指向精度优于±7μrad,位置精度优于±0.84 mm。本研究所组建的激光合束系统不仅具有合束精度高、校正速度快、光路扩展性强的优势,而且可实现激光束的周期性闭环校正,能够有效保证合束激光的长期工作稳定性。