電子於加速器中受磁鐵偏轉放出同步輻射光，須藉由高頻共振腔 (RF cavity) 內的電場加速以補充能量維持運轉，電子受加速同時也在腔內留下不規則的電場(尾場，wake field)，由傅立葉分析，可分解為共振腔中高次模 (Higher Order Mode) 的線性組合，因而造成下一時刻抵達腔內電子的不穩定 (multi-bunch instability)。本實驗室與德國BESSY合作開發無高次模高頻共振腔以期增加電子穩定性及運轉週期，主要使用HFSS程式模擬 CWCT (Circular Waveguide to Coaxial Transformer) 對高次模引出及吸收的情形，並描述 CWCT 長度對基模所造成的影嚮和與實驗作比較。

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