166.6-MHz superconducting cavities have been chosen for the High Energy Photon Source (HEPS) as the main accelerating structures to provide 900 kW of beam power and 5.4 MV of accelerating voltage. A proof-of-principle cavity adopting the quarter-wave beta = 1 geometry was previously developed. Excellent performance was achieved in vertical tests at cryogenic temperatures. The cavity was later welded with a helium jacket, dressed with a power coupler and other ancillaries, and high-power tested in a test cryomodule. Performance degradation was observed and analyzed. Evidence from temperature sensor readout and heat loss measurement results suggested an overheating in the cavity–coupler interface region causing a “thermal runaway” and eventually quenching the cavity at its design voltage. Electromagnetic-fluid-thermal coupled simulation has thus been conducted, and the hypothesis was nicely validated. Finally, solutions were proposed including an elongated niobium extension tube at the coupler port and an optimized helium gas cooling of the power coupler’s outer conductor. These modifications have been subsequently applied on the 166.6-MHz higher-order-mode damped superconducting cavities for the HEPS. Heat loss at 4.2 K contributed by the power coupler can be largely reduced with a modest gas cooling scheme. Similar design approaches can also be applied to other non-elliptical superconducting structures with on-cavity high-power coupler mountings.

中文翻译：

---

用于HEPS的166.6-MHz beta = 1超导四分之一波长谐振器的腔-耦合器接口的大功率测试和过热解决方案

高能光子源（HEPS）已选择166.6 MHz超导腔作为主要加速结构，以提供900 kW的束功率和5.4 MV的加速电压。先前已经开发出采用四分之一波β= 1几何形状的原理证明腔。在低温下的垂直测试中获得了出色的性能。后来，用氦套焊接了空腔，并穿上了功率耦合器和其他附件，并在测试低温模块中对其进行了高功率测试。观察并分析了性能下降。温度传感器读数和热损失测量结果的证据表明，空腔-耦合器界面区域过热，导致“热失控”，并最终以其设计电压淬灭空腔。因此进行了电磁-流体-热耦合模拟，并很好地验证了该假设。最后，提出了解决方案，包括在耦合器端口处使用细长的铌延长管，并对功率耦合器的外部导体进行优化的氦气冷却。这些修改随后应用于HEPS的166.6 MHz高阶模阻尼超导腔。功率耦合器在4.2 K时产生的热损失可以通过适度的气体冷却方案大大降低。类似的设计方法也可以应用于具有腔内大功率耦合器安装件的其他非椭圆形超导结构。提出了解决方案，包括在耦合器端口处使用细长的铌延长管，并对功率耦合器的外部导体进行优化的氦气冷却。这些修改随后应用于HEPS的166.6 MHz高阶模阻尼超导腔。功率耦合器在4.2 K时产生的热损失可以通过适度的气体冷却方案大大降低。类似的设计方法也可以应用于具有腔内大功率耦合器安装件的其他非椭圆形超导结构。提出了解决方案，包括在耦合器端口处使用细长的铌延长管，并对功率耦合器的外部导体进行优化的氦气冷却。这些修改随后应用于HEPS的166.6 MHz高阶模阻尼超导腔。功率耦合器在4.2 K时产生的热损失可以通过适度的气体冷却方案大大降低。类似的设计方法也可以应用于具有腔内大功率耦合器安装件的其他非椭圆形超导结构。