为提高磁铁单元预准直精度和工作效率,基于合肥先进光源设计了一套四路激光系统进行磁铁预准直.由于在实际布设四路激光系统时难以满足设计的角度和距离要求,针对影响四路激光布局精度的因素,着重分析了角度和距离对布局精度的影响规律,采用拟合误差指标和USMN(Unified spatial metrology network)权重分配优化平差方法进行四路激光系统的布局优化.通过优化USMN功能参数降低角度权重来提高磁铁单元预准直精度和工作效率;在定量分析粒子束的位置时,相比于其他指标,拟合误差比PDOP(Position dilution of precision)更能反映横向精度的变化,在粒子加速器准直测量领域更具优势.根据布局优化结果分析,直角正三棱锥为最佳布局,该布局的磁铁单元横向精度为7.5μm,满足合肥先进光源对磁铁单元预准直精度为10μm的要求.布局的角度会影响误差分布,且不同方向上的距离对精度的敏感程度有差异.所提设计对于四路激光系统实际布设具有一定的指导意义.
Layout Optimization of Four-Channel Laser Pre-Alignment System for Hefei Advanced Light Facility
Objective The Hefei Advanced Light Facility(HALF)is an international,advanced,fourth-generation synchrotron radiation light source in the low-energy region with world-leading design specifications for emissivity and brightness.However,challenges arise in the construction and operation of the HALF,one of which is the method to efficiently perform highly accurate pre-alignments.To improve the magnet pre-alignment accuracy and work efficiency,members at the HALF design a four-channel laser system for pre-alignment.Owing to space limitations,the actual four-channel laser system cannot fulfill the theoretical angle and distance requirements.Hence,the best layout for a four-channel laser system must be determined and the effects of angle and distance on the layout accuracy must be analyzed to improve the measurement performance of the four-channel laser system.Additionally,a simple and rapid adjustment method and an evaluation indicator suitable for accelerator alignment measurements are used to improve the efficiency of the four-channel laser system.Methods Fitting-error indicators and the unified spatial metrology network(USMN)weight-allocation-optimization adjustment method were used to optimize the layout of the four-channel laser system.The USMN weight-allocation-optimization adjustment dynamically adjusted the divergence-angle parameters to determine the most suitable parameter combination,reduce the angle weight,and improve the measurement accuracy.Meanwhile,the fitting-error evaluation was based on magnet points.The measured and theoretical values were used to perform a fitting conversion to obtain the fitting errors.We strictly derived the relationship between the fitting error and four-channel laser layout error and confirmed that the fitting error can be used as an indicator to evaluate the accuracy of the four-channel laser layout.The effects of angle and distance on the layout accuracy were analyzed to improve the measurement performance of the four-channel laser system.Results and Discussions The feasibility of the USMN weight-allocation-optimization adjustment method is investigated via simulation analysis.The divergence-angle error is dynamically adjusted to obtain the fitting errors of different parameter schemes,and the optimal parameter scheme is identified via comparative analysis(Table 1).Using the optimal parameter scheme,the adjustment is analyzed more comprehensively,and the result confirms that the adjustment can fully exploit the ranging information,avoid the interference of angle-measurement errors,and confirm the principle of modifying instrument parameters to adjust the distance and angle weights(Table 2-4).Additionally,four layout schemes are designed.Using the USMN weight-allocation-optimization adjustment method and fitting error,the right-angled regular triangular pyramid is shown to be the best layout.The position dilution of precision(PDOP)of the four layout schemes is calculated,which proves that an inaccurate random model affects the accuracy of the PDOP as a previous evaluation indicator.The fitting error is more suitable for alignment measurement than PDOP(Table 6).This study focuses on analyzing the effects of angle and distance on layout accuracy.In the actual layout process,ensuring that the top surface is an isosceles right triangle is not necessary.The vertex angle of the top surface is only required to be within[88°,94°],which satisfies the pre-alignment accuracy requirements of the HALF for the magnet unit(Fig.3).By improving the accuracy in the y-and z-directions,the overall layout accuracy of the four-channel laser can be improved without diminishing the lateral accuracy(Fig.4).The greater the absolute height difference in the z-direction,the higher is the overall layout accuracy of the four-channel laser.However,when combined with the actual layout of the pre-alignment experimental platform,if the instrument is installed at an extremely high position,then the amplification effect of the ground vibrations will severely affect the system stability.The absolute height difference in the z-direction should be set reasonably based on the actual situation(Fig.5).This study provides a theoretical basis for the actual layout of four-channel lasers.Conclusions In this study,a four-channel laser system is designed;additionally,the USMN weight-allocation-optimization adjustment method and the fitting error are used to optimize the four-channel laser layout.By optimizing the instrument parameters for this adjustment,the interference of angle-measurement errors on the measurement results is avoided and the measurement accuracy is improved.Compared with the PDOP as a previous evaluation indicator,the fitting-error index for the quantitative analysis of lateral accuracy is more suitable for particle-accelerator alignment measurements.The right-angled regular triangular pyramid layout demonstrates the highest accuracy,and the lateral accuracy of its magnet unit reaches 7.5 μm,which satisfies the pre-alignment requirements of the HALF.This study focuses on analyzing the effects of angle and distance on layout accuracy,thus providing a theoretical basis for the actual layout of four-channel lasers.
hefei advanced light facilityfour-channel laserspace joint precision control networkfitting errorlayout
万方数据
维普
