进一步提升同步光源束流品质的2.0K双cell超导高次谐波腔研究

The passive superconducting higher harmonic cavity operating at super fluid helium condition has the advantages of high cavity voltage, low dissipated power and short length cryomodule which will occupy smaller installation space of the valuable straight section in the storage ring. This project will focus on the research and design of a 1500MHz coupled two-cell passive superconducting cavity to improve the beam quality such as lifetime and stability in the medium energy synchrotron light source or future low emittance accelerators which suffer from the short lifetime. It is an initiate idea to develop this kind of cavity operating at super fluid temperature to be adopted in the storage ring as a harmonic cavity for bunch lengthening. The theory of beam quality improvement using this super-high Q-value harmonic cavity will be studied and development of a prototype cavity will be carried out in the project. Firstly,an optimized cavity string including the coupled two-cell niobium cavity, the thermal transition and the higher order mode dampers will be obtained to meet the requirements of physics, radio frequency and cryogenics specification.Secondly, before a niobium prototyping cavity is fabricated, using deep-drawing combined with electron beam wielding techniques, a cooper cavity will be fabricated to perform the fabricatioin techniques and rf measurment techniques research.And the Nb cavity inner surface will be polished by a set of surface processing methods and the influence from EP will be studied.Finally,the performance of the niobium prototype cavity will be obtained higher than Q0=1E10 @ Eacc=10MV/m in vertical test under super fluid liquid helium. The test technology for obtaining ultra-high gradient of this cavity will be explored. The successful results of the project will explore and establish the theory of applying a coupled two-cell higher harmonic cavity in light source for beam quality improvement.A high performance niobium prototype cavity will be fabricated and a set of fabrication and experimental techniques will be explored.

超流氦下工作的无源超导高次谐波腔具有单腔腔压高、功耗低、最大限度减少对直线节占用等优点，本项目将开展利用超流氦下工作、带腔间耦合的1500MHz双cell无源超导三次谐波腔，提高中能三代光源或未来低发射度光源的束流品质方面的理论研究和模型腔预制研究。首先提出并依据物理、射频和低温要求，优化设计超导三次谐波腔包括高次模深度抑制和宽模式间隔的铌腔、热过渡段和高次模吸收器等；其次，通过铜模型腔和纯铌腔的研制，开展研制工艺和射频测量技术研究；研究一系列表面处理工艺重点开展电化学抛光工艺，并探索获得超流氦下极限表面阻抗和加速梯度。本项目的成功实施将获得超流氦下带腔间耦合的双cell超导高次谐波腔的设计尺寸和铌腔性能指标Q0=1E10 @ Eacc=10MV/m，获得铌腔研制的一套标准流程和技术，为进一步的超导腔模组研制奠定基础，可为诸如上海光源等同步辐射光源束流品质的提高提供直接的科学依据。

超流氦下工作的无源超导高次谐波腔具有单腔腔压高、功耗低、最大限度减少对直线节占用等优点，本项目将开展利用超流氦下工作、带腔间耦合的1500MHz双cell无源超导三次谐波腔，提高中能三代光源或未来低发射度光源的束流品质方面的理论研究和模型腔预制研究。首先提出并依据物理、射频和低温要求，优化设计超导三次谐波腔包括高次模深度抑制和宽模式间隔的铌腔、热过渡段和高次模吸收器等；其次，通过铜模型腔和纯铌腔的研制，开展研制工艺和射频测量技术研究；研究一系列表面处理工艺重点开展电化学抛光工艺，并探索获得超流氦下极限表面阻抗和加速梯度。本项目的成功实施将获得超流氦下带腔间耦合的双cell超导高次谐波腔的设计尺寸和铌腔性能指标Q0=1E10 @ Eacc=10MV/m，获得铌腔研制的一套标准流程和技术，为进一步的超导腔模组研制奠定基础，可为诸如上海光源等同步辐射光源束流品质的提高提供直接的科学依据。