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1.3GHz椭圆腔上。一种新的强子SRF直线加速器正在开发中，它将以连续波（cw）射频功率工作。强子加速器的腔体采用横向电磁（TEM）加速模式，必须在5%到60%的光速范围内加速粒子速度，通常在100MHz到700MHz的射频频率范围内加速。该提案的PI使用了先前的发现拨款和RTI资金来支持学生和设备安装射频感应炉，为多个频率的射频低温测试[5]提供两个同轴腔，并通过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以学生为基础的研究项目，并利用TRIUMF SRF和材料科学基础设施。这里要求的资金将允许我们通过扩展我们的加工和测试设备来扩大同轴谐振器计划。目前的TEM模式大块铌腔几乎完全使用缓冲化学抛光（BCP）作为加工步骤，在制造后去除约150微米的损坏层或在加工步骤之间重置腔体的rf表面。由于比较研究表明，与BCP技术相比，椭圆腔群主要采用电抛光（EP）表面去除技术，因此高场性能得到了改善。此外，某些用于改善椭圆腔性能的新热处理，如N2掺杂[8]，需要后处理EP来优化处理。由于TEM模腔的复杂几何形状，只有少数实验室进行了极电位实验，并且没有研究比较在同一TEM腔上极电位和BCP的性能。此外，没有TEM模腔被N2掺杂处理过。我们建议通过该RTI购买设备，在两个同轴腔[15]上启用EP，使我们能够第一次比较相同TEM腔上的EP和BCP。此外，我们计划首次使用EP工艺允许在TEM模式腔中掺杂N2。为了扩大研究，我们建议购买TEM模式温度映射（T-map）系统的设备和部件，使我们能够区分局部或整体腔中的损失。这些信息对于更好地定义射频表面电阻与射频频率至关重要。我们还要求资金购买零件，以添加精确的低磁场磁探头，以便在冷却期间对腔体进行h映射。磁探针与T-map相结合将为我们提供几何相关磁捕获的详细信息。本提案中要求的RTI资金将提供一套独特的工具，以实现学生主导的发现科学，并在快速发展的SRF技术领域提供突破。

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.