Development of Superconducting Cavities for Future Synchrotron Light Sources and Electron-Positron Colliders

超导(SC)射频腔在恒波工作时提供了很高的加速场梯度，这比传统的正常导电(NC)腔高出好几倍。这种优越的性能在应用于高强度电子(正电子)存储环方面具有明显的优势，在高强度电子(正电子)存储环中，需要较少的腔体数量，以降低总的高阶模(Hom)阻抗，并避免束流不稳定。KEKB是一台用于B介子物理的电子-正电子对撞机，其中1.1A和2.6A的极高强度束流累积并相互碰撞，获得10^&lt；34；cm^&lt；-2&gt；S^&lt；-1&gt；为了保持如此高的束流强度，基于使用铁氧体吸收体的HOM减振方案的新的SC腔已经被开发并在电子环(HER)中投入使用。本研究项目的任务是弄清SC腔的性能，并建立高温…SC腔的运行技术。主要结果如下：1)在本研究项目中，束流强度逐渐提高，最终达到1.1A的满电流。这一结果表明，这种带有铁氧体吸收体的新型SC腔非常适用于各种领域的高强度存储加速器的射频腔。2)在如此高强度的工作状态下，该腔与束流有很强的相互作用。结果，仅仅是光束的微小移动就会干扰腔电压，并导致腔的跳闸。对所有跳模的分析研究表明，90%的跳模是由光束的不稳定性和损耗引起的。3)对输入耦合器的研究表明，外导体壁上发生了多脉冲放电，这与导体间直流偏置电压下的模拟结果一致。4)测量和分析了不同束流强度和束团结构下铁氧体阻尼器吸收的射频功率。结果表明，大范围HOMS产生的功率占主导地位，铁氧体阻尼器充分抑制了腔内所有HOMS的Q值，从而不会引起束流不稳定性。在束流较大的工作模式下，吸收功率已经达到设计水平的两倍以上。此外，对500 MHz腔型的研究给出了同步加速器光源环中SC腔的解决方案。因此，本研究项目明确了SC腔在大电流下使用的可行性。较少

Superconducting (SC) RF cavities provide a high accelerating field gradientin constant wave operation, which is several times higher than that achieved by conventional normal conducting (NC) cavities. This superior performance has a clear advantage in the application to high intensity electron (positron) storage rings, where the less number of cavities is desired so as to reduce the total higher order mode (HOM) impedance and to avoid beam instabilities.KEKB is an electron and positron collider for B meson physics, in which extreme high intensity beams of 1.1 A and 2.6 A are accumulated and collided each other to achieve a luminosity of 10^<34> cm^<-2>S^<-1>. To keep such a high intensity beam, new SC cavities based on a HOM damping scheme using ferrite absorbers have been developed and commissioned in the electron ring (HER). The mission of this research projefct is to make clear the performance of the SC cavities and also to establish the operation technology of SC cavities in high c … More urrent use.The important results will be summarized as follows.1) During this research project, the beam intensity has gradually been improved and finally reached the full current of 1.1 A. This result demonstrates that the new SC cavity with ferrite absorbers is quite useful as an RF cavity for high intensity storage accelerators in various fields.2) The cavity has a strong interaction with the beam in such a high intensity operation. As a result, just a small movement of the beam disturbs the cavity voltage and causes a trip of the cavities. Tfte analysis study of all the trips showed clearly that 90 % of die trips were caused by the instabilities and the loss of the beam. On the other hand, the SC cavity itself was quite stable, and tripped once or twice per month that was caused by discharging.3) The study of an input coupler demonstrated that multipacting discharging happened on the wall of outer conductor, which was in agreement with a simulation result under a DC bias voltage between the conductors.4) RF power absorbed by ferrite dampers has been measured and analyzed under various beam intensity and bunch configurations. The results show that the power caused by wide-range HOMs is dominant, and that the ferrite dampers sufficiently damps the Q of all the HOMs in th cavity so as not to introduce the beam instabilities. Because of an operation mode of higher bunch current, absorbed power has already reached two times higher than the design level.Besides these results, the study of a cavity shape of 500MHz gave a solution of the SC cavity in synchrotron light source rings. As a result this research project has made clear the feasibility of SC cavities in high current use. Less