Material Aspects of superconducting cavities beyond state of the art

超越现有技术水平的超导腔的材料方面

• 批准号: SAPIN-2021-00032
• 负责人: Junginger, Tobias
• 金额: $ 2.55万
• 依托单位: University of Victoria
• 依托单位国家: 加拿大
• 项目类别: Subatomic Physics Envelope - Individual
• 财政年份: 2022
• 资助国家: 加拿大
• 起止时间: 2022-01-01 至 2023-12-31
• 项目状态: 已结题
• 来源: https://www.nserc-crsng.gc.ca/ase-oro/Details-Detailles_eng.asp?id=763018
• 关键词: Material; Aspects; superconducting; cavities; beyond

Subatomic physics experiments rely on high energy charged particles supplied by particle accelerators. Radiofrequency cavities transform electromagnetic into kinetic energy. Superconducting technology is used worldwide for cavities requiring high efficiency, e.g in the ARIEL and ISAC-II linear accelerators at TRIUMF and the storage ring at the Canadian Light Source. Advanced surface and heat treatments have pushed the performance of state of the art elliptical cavities optimized to accelerate electrons close to fundamental material limitations in terms of power dissipation and maximum accelerating gradient, the latter being the energy gain of charged particles per unit length. Cavities are made of niobium metal sheets with a typical thickness of a few mm while the RF shielding currents only flow within a thin layer as superconducting currents decay exponentially over the length scale of the London penetration which is 32nm in case of clean niobium. Optimized performance is achieved by baking cavities in vacuum or in a low pressure gas atmosphere. These treatments alter the material properties such as the oxygen, hydrogen and vacancy concentrations of the outermost layer through diffusion processes. Depending on the desired performance characteristics different tailored treatments are chosen. For example different treatments yield highest accelerating gradients or lowest losses. Almost all future funded and proposed large scale accelerator facilities will require superconducting cavities, the largest project being the International Linear Collider (ILC) needing about 17000 cavities. If funded, ILC will use niobium cavities with an optimized surface treatment to be determined. Future upgrades will potentially employ superconductors beyond niobium. Optimizing niobium treatments and developing new materials for SRF applications both require in depth material science studies which are proposed here. Most SRF research has been performed on elliptical niobium cavities optimized to accelerate electrons. Advanced surface treatments beyond baking at 120C in vacuum have not been systematically studied on coaxial cavities optimized for relatively slow heavy particles as required for nuclear physics experiments. Coaxial cavities have different field configurations and are operated at lower RF frequencies. A direct translation of treatments from elliptical to coaxial cavities is not possible as the exact mechanisms for the obtained performance enhancements and how losses scale with RF frequency are not completely understood. A coordinated approach consisting of cavity testing and witness sample preparation at TRIUMF's SRF infrastructure with material science investigations at UVic is proposed to gain a better understanding of loss mechanisms in superconductors under radiofrequency exposure. The proposal seeks to establish a new research group in this field benefiting from available infrastructure at both institutes.

亚原子物理实验依赖于粒子加速器提供的高能带电粒子。射频腔将电磁能转化为动能。超导技术在世界范围内被用于需要高效率的腔体，例如在TRIUMF的ARIEL和ISAC-II线性加速器和加拿大光源的存储环中。先进的表面处理和热处理技术已经将最先进的椭圆腔的性能推向了最先进的椭圆腔，在功率耗散和最大加速梯度方面，加速电子接近基本的材料限制，后者是每单位长度带电粒子的能量增益。空腔由典型厚度为几毫米的铌金属片制成，而射频屏蔽电流仅在薄层内流动，因为超导电流在伦敦穿透的长度尺度上呈指数衰减，在清洁铌的情况下为32nm。优化性能是通过在真空或低压气体环境中烘烤空腔来实现的。这些处理通过扩散过程改变了材料的性能，如氧、氢和最外层的空位浓度。根据所需的性能特征，选择不同的定制处理。例如，不同的处理产生最大的加速梯度或最小的损失。几乎所有未来资助和提议的大型加速器设施都需要超导腔，最大的项目是国际直线对撞机（ILC），需要大约17000个腔。如果获得资助，ILC将使用具有优化表面处理的铌腔。未来的升级可能会使用铌以外的超导体。优化铌处理和开发用于SRF的新材料都需要深入的材料科学研究。大多数SRF研究都是在优化了加速电子的椭圆铌腔上进行的。超过120℃真空烘烤的高级表面处理尚未在核物理实验所需的相对慢重粒子优化的同轴腔中进行系统研究。同轴腔具有不同的场结构，并且在较低的射频频率下工作。从椭圆腔到同轴腔的直接转换处理是不可能的，因为所获得的性能增强的确切机制以及损耗如何随射频频率的变化而变化尚不完全清楚。提出了一种协调的方法，包括在TRIUMF的SRF基础设施进行空腔测试和见证样品制备，并在UVic进行材料科学研究，以更好地了解超导体在射频暴露下的损耗机制。该建议寻求在这一领域建立一个新的研究小组，利用这两个研究所现有的基础设施。