对 TRIUMF 超导直线加速器运行性能下降的研究以及缓解措施的改进研究

该项目旨在研究粒子加速器中的超导腔体性能下降问题，重点采用原位等离子体处理技术来减轻“场发射”现象。 该研究包括课程学习，随后通过分析等离子体参数进行实验，以提升腔体性能，最终将研究成果应用于 TRIUMF 的 ISAC-II 加速器。

Job description: Project description: Accelerating cavities are the heart of a particle accelerator. They transform the electromagnetic energy of a radio-frequency (RF) wave into kinetic energy, which is then transferred to a beam of charged particles. High-frequency electromagnetic fields (ranging from approximately 50 MHz to 1 GHz) resonating within superconducting niobium structures—reaching field gradients on the order of tens of megavolts per meter—enable powerful, continuous acceleration (utilizing tens of kilowatts of RF power) while dissipating only a few watts into the surrounding liquid helium. Over the years, it has been observed that some cavities in operational accelerators experience a gradual degradation in performance, characterized by the emergence or intensification of a parasitic phenomenon known as 'field emission.' This process, triggered by surface contamination that facilitates the emission and subsequent acceleration of electrons by electromagnetic fields, leads to the generation of ionizing X-ray radiation as the electrons undergo *bremsstrahlung* (braking radiation) upon striking material surfaces. This radiation not only creates safety concerns but also significantly increases the thermal load on the liquid helium bath. Typically, this necessitates the disassembly of the accelerator cryomodule in order to reprocess the accelerating cavities. In recent years, a highly promising treatment—applied, for instance, at the Spallation Neutron Source (SNS) accelerator—has made it possible to regenerate the performance of accelerating cavities *in situ*, thereby avoiding the need for the complete disassembly of faulty cryomodules. The technique involves generating a reactive gaseous plasma by exciting a resonant mode of the cavity using the existing RF system. This *in-situ* treatment has proven highly effective in mitigating the phenomenon of field emission. The PhD project, conducted under a joint supervision agreement between Université Paris-Saclay (UPS) and the University of Victoria (UVic), focuses on studying performance degradation during beam operation and improving mitigation strategies for TRIUMF’s superconducting linear accelerator (linac). The project is divided into three phases: - T0 to T0+6 months (UVic): Completion of coursework required for a doctoral degree in Canada. - T+6 months to T0+24 months (UPS): Exploratory studies on the impact of plasma parameters—such as plasma potential—to enhance the effectiveness of 'in-situ' plasma processing for superconducting accelerating cavities. These studies will be carried out at the 'Vide & Surface' (Vacuum & Surface) platform at IJCLab, which houses a plasma R&D test bench. The research will be supplemented by surface analyses using the multi-technique characterization equipment available on the platform. - T0+24 months to T0+42 months (UVic): Building on the optimization work performed at IJCLab, the plasma decontamination technique will be applied specifically to the cavities of TRIUMF’s ISAC-II accelerator. More advanced studies will be conducted at TRIUMF regarding the degradation of superconducting performance under beam exposure, as well as the interplay between plasma and thermal treatments.

所需背景与技能： 该职位已确定接收学生，因此不再接受申请。