低温二次电子产额测试系统设计与研究

在合肥先进光源（HALF）建设中，由低温超导材料组成的真空部件被大量使用，尤其是超导高频腔。超导腔以高加速梯度、低束流阻抗、高无载品质因数和低运行成本等特点，成为21世纪国际上拟建的大型加速器的首选。而超导腔和低温真空室内表面的二次电子发射可能会引发电子云（EC）现象。超剂量的二次电子倍增功率沉积会引起低温区域热负载增加、超导腔失超等现象，因此降低超导高频腔内二次电子发射成为合肥先进光源设计过程中的巨大挑战。在常温材料二次电子产额（SEY）测试系统的基础上，作者自主研发设计低温样品架结构，使液氦流经样品台并通过热传导冷却样品，计算漏热来反推所需要的制冷量和液氦的消耗速率。在系统集成调试后进行降温性能测试，搭建了低温材料二次电子测试系统。

Design and establishment of cryogenic secondary electron yield measurement system

In the construction of Hefei advanced light facility (HALF), vacuum components of superconducting materials are widely used, especially superconducting radio frequency cavity. The superconducting cavity with the characteristics of high accelerating gradient, low beam impedance, high unloaded quality factor and low operating cost has become the first choice for large accelerators in the 21st century. However, electron cloud (EC) phenomenon is generated by the secondary electron emission on the surface of the superconducting cavity and cryogenic vacuum chamber. Deposition of extra dose secondary electron multiplicative power can induce thermal load increase in the cryogenic zone, superconducting cavity quench and so on. Therefore, reduction of the secondary electron emission in the superconducting radio frequency cavity is a great challenge for the design of HALF. On the basis of secondary electron yield (SEY) measurement system for room temperature materials, the authors independently designed the cryogenic sample rack to allow liquid helium to flow through the sample stage and cool sample by heat conduction. It was significant to calculate heat leakage for deciding refrigerating capacity and liquid helium consumption rate. After the system integration and debugging, the cooling performance test was carried out. The results show that cryogenic SEY measurement system was established.