以同步輻射光束位置監測器之校正方法標準化與抑制非預測性耦合提升量測精度與磁鐵極化適應性

Standardized Calibration Method and the Nonpredictive Coupling Effect Suppressing for Accuracy and Magnet Polarization Adaptability Enhancement of a Synchrotron Radiation X-ray Beam Position Monitor

莊俊彥(Jyun-Yan Chuang)

指導教授 ： 顏家鈺

國立臺灣大學/工學院/機械工程學研究所/博士(2020年)

https://doi.org/10.6342/NTU202000758

摘要

台灣光子源(TPS)於2016年啟用，其運轉參數為電子束能量30億電子伏特，電流 400~500 mA，最佳光束波段範圍為軟X光及硬X光，屬於目前最廣泛使用之第三代同步輻射光源；其特色在於安裝插件磁鐵於儲存環中，使電子由第二代光源之偏轉一次變成多次偏轉，藉以大幅提升光源亮度，能夠更精確應用於許多尖端細微科學之研究。隨著第三代光源之光束尺寸的縮小，光束線實驗站對於光束位置之準直要求精度更加提升，透過TPS於前端區(Front End, FE)安裝之四刀片式X光束位置監測器(X-ray Beam Position Monitor System, XBPM)能夠量測出光子束位於加速器座標的位置，並提供給光束線用戶進行實驗試片對光準直。
考量XBPM自發展以來，未有研究針對刀片特性進行標準化提出完整之係數計算，因此本研究針對TPS XBPM發展出一套標準化校正方法，套用四象限位移感測器(Quadrant detector, QD)之校正概念，以XBPM之四刀片透過線性擬合進行刀片靈敏度標準化，並以系統化之概念將四刀片組合視為一個系統，輸入為光束強度，輸出為轉換之光束位置，求導出一組校正係數稱為”抑制矩陣”來抑制非預期耦合飄移，藉由去耦合使XBPM量測值位於加速器座標上X與Y之位移量測能夠具備獨立性，有利於實驗站獲得正確光束位置進行準直以及光束穩定性監測。經過校正後之XBPM能夠於最佳量測範圍±100 μm內得到小於1 μm的耦合飄移誤差，光束位移量測值在系統線性範圍內之量測誤差小於2 μm，與校正前或傳統之校正方法相比，本研究大幅提高量測準確性。在不同磁鐵極化適用性方面，對於橢圓聚頻磁鐵之不同極化模式下，本校正方法仍具備其相容性，實驗結果顯示，若以水平線性極化模式下進行之校正係數套用於圓極化模式，仍可得到誤差5 μm之量測誤差精度，但若要求更高之精度，可使用本系統建立之快速掃描之方式得到新的校正係數；相較於一般傳統校正方法，本研究所提出之校正方法具有較廣泛之量測應用。
利用數位訊號處理器Libara Photon所提供之完整暫存器，結合自動化束流調控(Beam steering)與分散式嵌入系統進行邊緣計算(Edge computing) 建立大數據資料庫，能夠有效率地完整化XBPM校正工程，對於XBPM與插件磁鐵參數之強相依特性來說，本研究所建立之系統能夠自動化對應不同間隙或極化模式償準確之校正係數，改善傳統XBPM應用精度，將其實用性與可靠度大幅提升，對於高準直需求的光束線有其極大助益，也是本研究最主要之貢獻。

關鍵字

四刀片式X光束位置監測器 ； 抑制矩陣 ； 非預期耦合飄移 ； 極化適用性

並列摘要

The Taiwan Photon Source (TPS) was launched in 2016 with the operating parameter of an electron beam energy of 3 GeV and a current of 400-500 mA. The best energy bandwidth of the TPS is within the range of soft X-rays to hard X-rays, and it is considered to be a 3rd-generation synchrotron radiation source that is widely used at present. The main feature is the installation of the insertion device (ID) in the storage ring to enhance the brightness of the photon beam source, the electron beam polarized by IDs makes the intensities higher than previous generation synchrotron source. The ID includes the following types: Wiggler, In-vacuum Undulator (IU) and Elliptically Polarized Undulator (EPU). The purpose is to turn the electron from the single deflection in a 2nd-generation light source to multiple deflections, thereby improving the brightness. The TPS can further be more accurately applied to research in cutting-edge science fields, such as material geometry, atom or molecular properties, semiconductors, chemical materials and magnetic structures.
With the reduction in the beam size of the 3rd-generation light source, the beamline experiment station requires more accurate alignment of the beam position. Through the four-blade X-ray beam position monitoring system (XBPM) installed in the front end (FE) of TPS, the photon beam position in the accelerator coordinate system can be measured for the experimental requirement of the beamline user. Since the development of the XBPM, there has been no research on characteristic standardization of blade, and a complete coefficient calculation has been proposed. Therefore, in this study, to detect the photon beam position of TPS, a set of XBPM standardization methods has been developed. This approach applied the quadrant detector (QD) calibration concept, where the sensitivity of the four blades of the XBPM could be standardized through the linear fitting, and used the concept of systematization to regard the assembly of four blades as an integrated system. The input was the photon beam intensity, the output was the converted beam position, and a set of correction coefficients called the "suppression matrix" was derived to suppress the nonpredictive coupling drift error during the monitoring and to decouple the displacement in terms of X and Y on the accelerator coordinate system independently. The XBPM that was used for beam alignment at the beamline experimental station to obtain the correct beam position or monitor the beam stability offered a significant enhancement. After the calibration, the XBPM could achieve results with a coupling drift error of less than one μm in the best measurement range of ± 100 μm. The measurement error of beam displacement in the linear range was less than two μm compared with the conventional calibration method, showing that the method in this study improved the measurement accuracy significantly. In terms of the adaptability of different polarization modes, this method still offered excellent compatibility with the different polarization modes of the EPU. The experimental results showed that if the calibration coefficients applied in the horizontal linear polarization mode were applied to the circular polarization mode, the measurement was still accurate to within an error of 5 μm. However, if a higher accuracy was required, the fast scanning technique established by this system could be used to obtain new calibration coefficients. In comparison with the conventional calibration methods, the method in this study showed higher adaptability for measurement applications.
By using the complete registers provided by the digital signal processor Libara Photon along with the automatic beam steering and distributed embedded edge computing system to build an extensive database, the XBPM calibration engineering could be efficiently integrated. Therefore, in terms of the strong dependency of the XBPM and ID gaps, the system in this study could automatically and accurately compensate with the calibration coefficients in correspondence to the different gaps or polarization modes, change the conventional application accuracy of the XBPM, and greatly improve its practicability and reliability. This approach is highly helpful in the case of high demand for precision and alignment of the beamline, which significantly contributed to this study.

並列關鍵字

four-blade X-ray beam position monitor ； suppression matrix ； nonpredictive coupling drift ； adaptability of different polarization modes

參考文獻

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