Low cost vibrating sample magnetometer to study materials for superconducting radiofrequency cavities

国际直线对撞机(ILC)需要大约17000个由超导材料Nb制成的超导射频腔。如今，在可实现的加速梯度和品质因数方面，铌腔的性能接近它们的基本极限。后者是低温效率的量度，而加速梯度是单位长度的能量增益，并最终将所需能量输出的极限设定为直线加速器的长度。目前，最大的加速梯度是用正常的导电技术实现的，但以低占空比和效率为代价。因此，对于ILC的能源升级，目前正在考虑普通和超导方案。超导腔需要在无磁通的迈斯纳状态下运行，以避免磁涡的耗散。由于加速梯度与表面磁场成正比，第一涡穿透场限制了加速梯度的大小。已经提出了几种利用薄膜新型超导体、纳米薄层超导体和绝缘体交替使用或在真空或低压气体气氛中进行热处理的方法。在所有情况下，目标都是保持迈斯纳态(无涡旋超导态)在比块状Nb技术更高的磁场中。几项研究表明，层状结构之间的界面为磁通穿透提供了额外的能量屏障[T.Kubo Supercond。SCI。泰克诺。卷30,023001页(2017年)]以及通过邻近效应恢复缺陷附近序参数的稳定性[T.Junginger等人]。超级棒。SCI。《技术》，第30卷，125012页(2017年)]。要阐明层状超导体的机制和有效性，需要探测界面附近每一层的局部磁相，以及相同样品上的第一磁通穿透场。使用直流方法进行样本研究可以更快、更准确地测量基本极限场，而不受射频表面条件的影响，也不需要建立整个腔体。为了研究每一层的磁相，NSERC通过项目发现赠款资助了Beta-SRF设施。在这方面，需要提供资金来开发一种振动样品磁强计，以测量同一样品上的第一个涡旋穿透场，以预测可实现的最大加速梯度。与商业仪器相比，在大学里开发仪器的成本要低得多，并为学生开发和操作这种仪器提供了巨大的机会。

The International Linear Collider (ILC) requires about 17000 superconducting radiofrequency cavities made of the superconducting material niobium. Nowadays niobium cavities perform close to their fundamental limit in terms of achievable accelerating gradient and quality factor. The latter is a measure of the cryogenic efficiency while the accelerating gradient is the energy gain per unit length and ultimately sets the limit to the length of a linear accelerator for a required energy output. Currently, largest accelerating gradients are achieved with normal conducting technology but at the cost of low duty cycle and efficiency. Therefore, for an energy upgrade of ILC normal and superconducting options are currently being considered. Superconducting cavities need to be operated in a flux free Meissner state to avoid dissipation from magnetic vortices. As the accelerating gradient is directly proportional to the surface magnetic field the field of first vortex penetration sets the limitation for the accelerating gradient. Several routes have been proposed using thin film novel superconductors, alternating nanometer thin layers of superconductors and insulators or Nb heat treated under vacuum or in low pressure gas atmosphere. In all cases, the goal is to sustain the Meissner state (vortex free superconducting state) at a higher field compared to bulk Nb technology. Several studies have suggested that the interface between the layered structure provides an additional energy barrier for flux penetration [T. Kubo Supercond. Sci. Technol. vol. 30, p. 023001 (2017)] as well as recovering the stability of the order parameter near defects via the proximity effect [T. Junginger et al. Supercond. Sci. Technol., vol. 30, p. 125012 (2017)]. Elucidating the mechanism and effectiveness of layered superconductors will require probing the local magnetic phase at each layer near the interface and the field of first flux penetration on identical samples. Sample studies with DC methods can allow a quicker and more accurate measurement of the fundamental limiting field without being affected by RF surface conditions and without building entire cavities. To study the magnetic phase at each layer NSERC has funded the beta-SRF facility through a project discovery grant. Here funding is requested to develop a vibrating sample magnetometer to measure the field of first vortex penetration on the same samples to predict the maximum achievable accelerating gradient. Compared to a commercially available instrument developing the instrument at the university will be significantly cheaper and give great opportunities for students developing and operating this instrument.