超导腔垂直测试数字化自激励环路研制

Development of digital self-excited loop in vertical tests of superconducting cavity

介绍北京大学垂直测试系统的数字化自激励环路系统,重点分析了实际测试中避免多单元(cell)超导腔模式串扰的方法以及偏离四倍频采样对信号幅度和相位的影响。该系统运行稳定可靠,可有效区分1.3 GHz8π/9模,解决了多cell超导腔测试中模式串扰问题。分析了超导腔自激励环路在垂直测试中的应用,介绍了北京大学垂直测试系统的数字化自激励环路,采用上下变频方案的射频前端和包括有限脉冲响应滤波器的数字算法,系统简洁扩展性强。重点分析了实际测试中避免多cell超导腔模式串扰的方法以及偏离四倍频采样对信号幅度和相位的影响。在多种不同频率超导腔的垂直测试中该系统运行稳定可靠,可有效区8π/9模,解决了多cell超导腔测试中模式串扰问题。

Vertical tests are very important for superconducting cavity after its post-processing. The aim is to obtain the quality factor versus accelerating gradient curve to evaluate a cavity’s performance. Because of its narrow bandwidth, the superconducting cavity should work stably in the resonant state during the vertical tests. The digital self-excited loop system for the vertical test stand of Peking University is introduced in this paper. The methods of avoiding crosstalk during multi-cell superconducting cavity test were brought out. The influence of deviation from quadruple frequency sampling on amplitude and phase was analyzed. The system is stable and reliable, can effectively8π/9 crosstalk in multi-cell superconducting cavity test.