利用幾種不同的量測與分析方法來研究同步輻射加速器磁鐵的磁場特性

Abstract

中文提要:為了量測及分析第三代同步輻射加速器的磁格及內插元件磁鐵 的磁場特性，作者改進開發了幾種不同的高精確度磁場量測及分析方法。 這些方法包括(1)利用固定霍耳探針的角度在三度空間量測，進行高精確 度的每個諧項磁場分量分析法(2)利用三個互相垂直的霍耳探針配合飛行 式的點磁場量測(3)利用三度空間旋轉式Helmholtz線圈量測方法進行三個 磁偶極矩分量的量測以及(4)利用長迴路線圈的量測方法進行兩個積分場 分量的量測。作者藉由這些方法所得的數據，修正了同步輻射的缺陷磁鐵 並控制其磁場品質，而動力射束小組，再藉由量測的磁場特性，來調整磁 格常數，使儲存環得以操作在最佳狀度。第一種方法是固定霍耳探針的角 度再配合三度空間的磁場掃描方法，然後再利用正交分析原理可以很精確 地分析出磁格磁鐵的多極項分量。這套量測方法具有自動控制與數據讀取 的功能，而霍耳探針的溫度，被控制在±0.1℃。這套磁場量測系統的精 確度保持在0.01％以內，同時這種精確度足夠用來分析以及對磁格磁鐵的 除錯。第二種方法是利用一種三個互相垂直的霍耳探針配合飛行式的量測 方法可以用來同時量測到三個磁場分量，在這種量測方法之下雖然沒有對 霍耳探針做溫度控制，但其同時對霍耳電壓與霍耳探針溫度做磁場校正， 除此之外，三個霍耳探針的相互垂直度，磁場中心置位和霍耳平面效應也 都必需做校正。經由這個方法所量測與分析出的結果可以做為內插元件磁 鐵的多極項以及光譜的修正依據，這套系統的積分場量測精度為10 而磁 場強度的精度為2 Gauss。第三種方法是利用Helmholtz線圈再配合三個自 由度的旋轉機構可以用來快速量測大量磁塊的三個磁偶極矩分量，根據這 些磁偶極矩的量測結果再配合洗排模擬方法來降低內插元件磁鐵的磁場誤 差。這套量測方法在主軸磁場的量測精度為0.04%而對另外兩個分量的角 度量測精度在0.02o。第四種方法是使用長回路線圈，這種線圈配合“動 態掃描”與“靜態掃描”方法可以增加磁場的量測速度，這種方法可以用 來了解每個磁塊的磁場均勻性及整個內插元件磁鐵的多極磁場分量的積分 值，這種量測方法也可以用來與霍耳探針量測方法做量測結果的確定。這 個量測結果可以提供做磁塊篩選使得內插元件磁鐵的磁場能夠好到某一個 程度，這套系統是屬於快速且高精度的量測方法。在“靜態掃描”方法的 精確度大約在5 ，而“動態掃描”方法大約是在10 。最後，利用這些量 測方法來量測與分析各種磁鐵的特性，如最主要的磁格磁鐵－二極、四極 、六極磁鐵，還有內插元件磁鐵－可調式之改變相位與改變間隙的聚頻磁 鐵。這些量測與分析的結果可以提供我們修正錯誤磁鐵的依據。整個詳細 的量測方法以及磁鐵的缺陷修正過程還有量測與分析結果將在後文討論。 英文提要: The author had improved and developed various high accuracy and precision field measurement and analysis methods to characterize the magnetic field features of the third generation synchrotron accelerator magnets. These methods include (1) Using a fixed angle Hall probe and associated with 3-D mapping trajectory to perform the high precision harmonic field components analysis of lattice magnets; (2) Using a three- orthogonal Hall probe and associated with the “on the fly” mapping method for point field measurement of the insertion device magnets; (3) Using a three-dimension rotation mechanism that associated with the Helmholtz coil method to analyze the three components of magnetic dipole moment; and (4) Using the long loop coil measurement method to analyze the two transverse components of the integral field strength. Meanwhile, the author had depended on these methods to correct the defect magnet and control the field quality of the whole synchrotron accelerator magnets. The beam dynamic group people in SRRC had also depended on the field features to tune the lattice parameter such that the storage ring had been operated in an optimum condition. Firstly, a fixed angle Hall probe with temperature control and associated with the 3-D mapping trajectory method to measure the lattice magnet. This is an automatic control and data acquisition system that had associated with the orthogonal analysis principle precisely to characterize the harmonic field components of the lattice magnets. The Hall probe temperature was controlled within 0.1o C. The precision and accuracy of this harmonic field component measurement and analysis method is around 0.01% that is enough to characterize the lattice magnets. The field measurement results by this method are analyzed and successfully to modify the defect magnet.Secondly, a three- orthogonal Hall probe with “on the fly” mapping method had also been developed to measure the three magnetic field components simultaneously. The field strengths of the three Hall probes were calibrated with respect to Halltemperature and the induced Hall voltage. In addition, the orthogonal angle, threecenter-positions, and the planar Hall effect were also calibrated and readjusted carefully to minimize the system error. The field measurement and analysis results by this method can be used to perform the multipole and spectrum shimming for theinsertion device magnets. The precision of this system is about 20 G□cm for fieldintegral and 2 G for field strength. Thirdly, a Helmholtz coil system associated with a three-degree of freedom rotation mechanism which had been designed and completed. This system was used for measuring the three magnetic dipole moments of the large number of permanent magnet blocks. The measurement results associated with the simulated annealing method to sort the magnets. This method can be used to minimize the field error of the whole insertion device magnets. The long term precision of this system is 0.04% forthe easy component and 0.02o for the other two minor components. Fourthly, a long loop coil system with “dynamic scan” and “static scan”measurement method was also available to measure the integral field strength and enhance the measurement speed. The long loop coil system is a high speed and high precision measurement method, the precision is around 5 G□cm on the “static sca” method and 10 G□cm on the “dynamic scan” method. This method can be used to characterize the integral multipole field profile of each magnet block and the whole insertion device. It can also serve as a double-check of the Hall probe measurement method. The integral multipole field measurement results can provide the informationof the field homogeneity of each magnet block to perform the magnet sorting that will maintain the field quality as good as possible.Finally, These methods are successfully to measure and analyses the main lattice magnets □ dipole, quadrupole, sextupole, the small corrector magnets; and the insertion device magnet □ adjustable phase and gap undulator magnet. These measurement and analysis results can be used as a figure-of-merit in debugging the defect magnet and to perform the shimming and chamfering for the multipole and spectrum correction.Details of the measurement method, and the magnetic field measurement and analysis results will be presented and discussed in the text.