Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
Cornell University, Ithaca, New York, USA
University of Minnesota, Minnesota, USA
Next-generation, thin-film surfaces employing Nb₃Sn, NbN, NbTiN, or other compound superconductors are essential for reaching enhanced RF performance levels in SRF cavities. However, optimized, advanced deposition processes are required to enable high-quality films of such materials on large and complex-shaped cavities. For this purpose, Cornell University is developing a plasma-enhanced chemical vapor deposition (CVD) system that facilitates coating on complicated geometries with a high deposition rate. This system is based on a high-temperature tube furnace with a high-vacuum, gas, and precursor delivery system, and uses plasma to significantly reduce the required processing temperature and promote precursor decomposition. Here we present an update on the development of this system, including final system design, safety considerations, assembly, and commissioning.
Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
Cornell University, Ithaca, New York, USA
The native niobium oxide layer present on niobium has been shown to affect the performace of superconducting RF cavities. Extremely thin layers of gold on the surface of niobium have the potential to suppress surface oxidation and improve cavity performance. However, depositing uniform layers of gold at the desired thickness (sub-nm) is difficult, and different deposition methods may have different effects on the gold surface, on the niobium surface, and on the interface between the two. In particular, the question of whether gold deposition actually passivates the niobium oxide is extremely relevant for assessing the potential of gold deposition to improve RF performance. This work builds on previous research studying the RF performance of gold/niobium bilayers with different gold layer thicknesses. We here consider alternative methods to characterize the composition and chemical properties of gold/niobium bilayers to supplement the previous RF study.
Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
Cornell University, Ithaca, New York, USA
Nb₃Sn is a promising alternative material for SRF cavities that is close to reaching practical applications. To date, one of the most effective growth methods for this material is vapor diffusion, yet further improvement is needed for Nb₃Sn to reach its full potential. The major issues faced by vapor diffusion are tin depleted regions and surface roughness, both of which lead to impaired performance. Literature has shown that the niobium surface oxide plays an important role in the binding of tin to niobium. In this study, we performed various chemical treatments on niobium samples pre-nucleation to enhance tin nucleation. We quantify the effect that these various treatments had through scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). These methods reveal information on tin nucleation density and uniformity, and a thin tin film present on most samples, even in the absence of nucleation sites. We present our findings from these surface characterization methods and introduce a framework for quantitatively comparing the samples. We plan to apply the most effective treatment to a cavity and conduct an RF test soon.
Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
Cornell University, Ithaca, New York, USA
Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
The first experimental studies of zirconium-doped surfaces verified that zirconium can enhance the critical temperature of the surface, resulting in a lower BCS resistance than standard-recipe niobium. However, they also produced a disordered oxide layer, resulting in a higher residual resistance than standard-recipe niobium. Here, we show that zirconium-doped surfaces can grow well-behaved thin oxide layers, with a very thin ternary suboxide capped by a passivating ZrO2 surface. The elimination of niobium pentoxide may allow zirconium-doped surfaces to achieve low residual resistance.
Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
Cornell University, Ithaca, USA
Materials scientists seek to contribute to the development of next-generation superconducting radio-frequency (SRF) accelerating cavities. Here, we summarize our achievements and learnings in designing advanced SRF materials and surfaces, including Nb₃Sn [1¿3], ZrNb(CO) [4, 5], and Au/Nb surface design [6,7]. Our efforts involve electrochemical synthesis, phase transformation, and surface chemistry, which are closely coupled with superconducting properties, SRF performance, and engineering considerations. We develop electrochemical processes for Sn, Zr, and Au on the Nb surface, an essential step in our investigation for producing high-quality Nb₃Sn, ZrNb(CO), and Au/Nb structures. Additionally, we design a custom chemical vapor deposition system to offer additional growth options. Notably, we find the second-phase NbC formation in ZrNb(CO) and in ultra-high-vacuum baked or nitrogen-processed Nb. We also identify low-dielectric-loss ZrO2 on Nb and NbZr(CO) surfaces. These advancements provide materials science approaches dealing with fundamental and technical challenges to build high-performance, multi-scale, robust SRF cavities for particle accelerators and quantum applications.
Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
Cornell University, Ithaca, New York, USA
Niobium-3 tin is a promising material for next-generation superconducting RF cavities due to its high critical temperature and high theoretical field limit. There is currently significant worldwide effort aiming to improve Nb₃Sn growth to push this material to its ultimate performance limits. This talk will present an overview of Nb₃Sn cavity development at Cornell University. One approach we are pursuing is to further advance the vapor diffusion process through optimized nucleation and film thickness. Additionally, we are exploring alternative Nb₃Sn growth methods, such as the development of a plasma-enhanced chemical vapor deposition (CVD) system, as well as Nb₃Sn growth via electrochemical synthesis.