Processing and testing equipment for Coaxial Test Resonators

优化和理解超导射频（SRF）性能的研究主要集中在用于电子加速的椭圆形1.3GHz腔。一种新的强子SRF线性加速器正在开发中，它将使用连续波（cw）射频功率运行。强子加速器的腔体采用横向电磁（TEM）加速模式，粒子速度必须在光速的5%~60%之间变化，射频频率通常在100 MHz ~ 700 MHz之间。 该提案的PI已使用先前的发现补助金和RTI资金支持学生和设备安装射频感应炉，在多个频率下为射频低温测试提供两个同轴腔[5]，并使用muSR和β-NMR探索Nb和新材料的性能[1，2，3，4，6]。所有的设备都是为了支持学生为基础的研究计划，并利用TRIUMF SRF和材料科学基础设施。这里要求的资金将使我们能够通过扩大我们的加工和测试设备来扩大同轴谐振器计划。目前的TEM模式体铌腔几乎完全使用缓冲化学抛光（BCP）作为制造后去除约150微米损伤层或在处理步骤之间重置腔的射频表面的步骤。椭圆腔社区主要使用电抛光（EP）表面去除，因为比较研究表明，高场性能比BCP技术得到改善。此外，某些新的热处理，如N2掺杂[8]，用于改善椭圆腔的性能，需要后处理EP来优化处理。 由于TEM模腔的复杂几何形状，仅在少数实验室中进行了EP [7]，并且没有研究在同一TEM腔上比较EP与BCP的性能。此外，没有TEM模腔用N2掺杂处理。我们建议通过该RTI购买设备，以使两个同轴腔上的EP [15]允许我们首次比较同一TEM腔上的EP与BCP。此外，我们还计划使用EP工艺首次允许TEM模腔的N2掺杂。为了加强研究，我们建议购买TEM模式温度映射（T-map）系统的设备和部件，使我们能够区分腔体中的局部或全局损耗。这些信息对于更好地定义射频表面电阻与射频频率的关系至关重要。我们还要求资金购买零件，以增加准确的低场磁探头，以便在冷却期间也能对腔体进行H映射。磁探针结合T图将为我们提供与几何形状相关的磁通捕获的详细信息。本提案中要求的RTI资金将提供一套独特的工具，以使学生能够领导发现科学，并在快速发展的SRF技术领域取得突破。

Studies to optimize and understand superconducting radio-frequency (SRF) performance have been primarily focused on elliptical 1.3GHz cavities for electron acceleration. A new wave of hadron SRF linear accelerators are being developed that will operate with continuous wave (cw) rf power. The cavities for hadron accelerators utilize the transverse electric and magnetic (TEM) accelerating mode and must accelerate a wide range of particle velocities from 5% to ~60% the speed of light and with rf frequencies ranging from 100MHz to 700MHz typically.  The PI on this proposal has used a previous Discovery grant and RTI funds to support students and equipment to install an rf induction oven, to source two coaxial cavities for rf cryogenic testing [5] at multiple frequencies and to explore the performance of Nb and new materials with muSR and beta-NMR [1,2,3,4,6]. All the equipment is geared to support student based research programs and leverages TRIUMF SRF and material science infrastructure. The funds requested here will allow us to augment the coaxial resonator program by expanding our processing and testing equipment. Present TEM mode bulk Niobium cavities almost exclusively use Buffered Chemical Polish (BCP) as a step to remove ~150microns of damaged layer after fabrication or to reset the rf surface of the cavity between processing steps. The elliptical cavity community primarily uses Electropolish (EP) surface removal  since comparative studies show that the high field performance is improved over the BCP technique. Also, certain new heat treatments like N2 doping [8] applied to improve the performance of elliptical cavities need a post-treatment EP to optimize the treatment.  Due to the complex geometry of TEM mode cavities, EP has been done in only a few Labs [7] and no studies have been done to compare the performance of EP vs BCP on the same TEM cavity. Further, no TEM mode cavity has been treated with N2 doping. We propose to purchase equipment through this RTI to enable EP on the two coaxial cavities [15] to allow us to, for the first time, compare EP vs BCP on the same TEM cavity. Further we plan to use the EP process to allow N2 doping of the TEM mode cavities also for the first time. To augment the study we propose to purchase equipment and parts for a TEM mode temperature mapping (T-map) system to enable us to discern between localized or global losses in the cavities. Such information is crucial to better define rf surface resistance vs rf frequency. We also request funds to procure parts to add accurate low field magnetic probes to allow also H-mapping of the cavity during cooldown. The magnetic probes in combination with T-map will give us detailed information on geometry dependent flux trapping. The RTI funds requested in this proposal will provide a unique set of tools to enable student led discovery science and provide breakthroughs in the rapidly evolving SRF technology sector.