同步輻射光的提供過程中，提供高加速電壓梯度的共振腔體由於冷卻效應與壓差變化，造成結構變形，而改變腔內電磁場共振模態，導致頻率飄移，造成同步輻射光源品質的下降。本文以套裝軟體ANSYS作結合場域的分析，首先探討1.5GHz 圓柱盒型(pill-box)共振腔，因為溫度與壓力使其結構發生變形後，內部電磁場特性：加速電場、橫向磁場及工作頻率飄移現象。結果顯示，共振腔體開口太大會造成不規則電場使工作基頻飄移；而加長兩端延伸管可穩定加速電場；共振腔體中心長度延長可增加結構變形，但在一定範圍內，腔體共振基頻並無明顯改變；在4.2K超低溫時，因冷卻效應，使共振腔的工作頻率飄移達3MHz，但仍在允許範圍內。
其次，利用結構形狀單純的圓柱狀共振腔體模型，在不同溫度環境下，施予不同的外加負載，藉由其電磁場共振頻率的變化，反推出其材料的機械性質；採用與上述相同的分析流程，對共振腔體在特定溫度下，分析不同材質以及不同厚度的腔體在抽真空過程中，內部電磁場共振頻率變化，得知內部電磁場頻率飄移量與壓差、熱收縮量呈正比，與楊氏係數、浦松比、腔體厚度成反比；利用此分析結果建立頻率飄移量(可實際量測的物理量)與材料性質、腔體尺寸之間的數學關係式，並實際量测鋁合金共振腔體(室溫

In order to supply synchrotron radiation of higher quality, a storage ring with a high frequency resonant cavity is necessary to accelerate the electron beam. In operating environment, the pressure and temperature difference may cause structural deformation in the cavity, which results in the instability of interior electron beam, the working frequency fluctuation and the degradation of light source quality. In this paper, the interior electromagnetic characteristics of a 1.5GHz pill-box resonant cavity is obtained using the ANSYS code by combining the structural and electromagnetic analyses. The results showed that the resonant frequency would fluctuate more severely for a cavity with bigger aperture and shorter wave-guide’s length. Under the condition of thermal contraction from room temperature to liquid Helium temperature and 1atm external pressure, the pill-box cavity would produce a tolerable 3MHz of frequency fluctuation.
The cryogenic characteristics of material properties were found based on the frequency drift in different environment temperature and loading. By the parametric study, the results show that the frequency increases for larger thermal contraction and external pressure; however, the frequency decreases for increasing Young’s modulus, Poison’s ratio and cavity thickness. Finally, the cryogenic material properties of an aluminum cavity were obtained by combing the above numerical procedure and experiment to measure the frequency drift for verification.

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