Temperature, RF Field, and Frequency Dependence Performance Evaluation of Superconducting Niobium Half-Wave Coaxial Cavity

Recent advancement in superconducting radio frequency cavity processing techniques, with diffusion of impurities within the RF penetration depth, resulted in high quality factor with increase in quality factor with increasing accelerating gradient. The increase in quality factor is the result of a decrease in the surface resistance as a result of nonmagnetic impurities doping and change in electronic density of states. The fundamental understanding of the dependence of surface resistance on frequency and surface preparation is still an active area of research. Here, we present the result of RF measurements of the TEM modes in a coaxial half-wave niobium cavity resonating at frequencies between 0.3 - 1.3 GHz. The temperature dependence of the surface resistance was measured between 4.2 K and 1.6 K. The field dependence of the surface resistance was measured at 2.0 K. The baseline measurements were made after standard surface preparation by buffered chemical polishing

Lower Temperature Annealing of Vapor Diffused Nb\u3csub\u3e3\u3c/sub\u3eSn for Accelerator Cavities

Nb3Sn is a next-generation superconducting material for the accelerator cavities with higher critical temperature and superheating field, both twice compared to Nb. It promises superior performance and higher operating temperature than Nb, resulting in significant cost reduction. So far, the Sn vapor diffusion method is the most preferred and successful technique to coat niobium cavities with Nb3Sn. Although several post-coating techniques (chemical, electrochemical, mechanical) have been explored to improve the surface quality of the coated surface, an effective process has yet to be found. Since there are only a few studies on the post-coating heat treatment at lower temperatures, we annealed Nb3Sn-coated samples at 800 C - 1000 C to study the effect of heat treatments on surface properties, primarily aimed at removing surface Sn residues. This paper discusses the systematic surface analysis of coated samples after annealing at temperatures between 850 C and 950 C

Surface Properties and RF Performance of Vapor Diffused Nb₃Sn On NB After Sequential Anneals Below 1000 °C

Nb₃Sn is a next-generation superconducting material that can be used for future superconducting radiofrequency (SRF) accelerator cavities, promising better performance, cost reduction, and higher operating temperature than Nb. The Sn vapor diffusion method is currently the most preferred and successful technique to coat niobium cavities with Nb₃Sn. Among post-coating treatments to optimize the coating quality, higher temperature annealing without Sn is known to degrade Nb₃Sn because of Sn loss. We have investigated Nb₃Sn/Nb samples briefly annealed at 800-1000 °C, for 10 and 20 minutes to potentially improve the surface to enhance the performance of Nb₃Sn-coated cavities. Following the sample studies, a coated single-cell cavity was sequentially annealed at 900 °C and tested its performance each time, improving the cavity’s quality factor relatively. This paper summarizes the sample studies and discusses the RF test results from sequentially annealed SRF Nb₃Sn/Nb cavity

Nb\u3csub\u3e3\u3c/sub\u3eSn Coating of Twin Axis Cavity for SRF Applications

The twin axis cavity with two identical accelerating beams has been proposed for energy recovery linac (ERL) applications. Nb3Sn is a superconducting material with a higher critical temperature and a higher critical field as compared to Nb, which promises a lower operating cost due to higher quality factors. Two niobium twin axis cavities were fabricated at JLab and were proposed to be coated with Nb3Sn. Due to their more complex geometry, the typical coating process used for basic elliptical cavi-ties needs to be improved to coat these cavities. This development advances the current coating system at JLab for coating complex cavities. Two twin axis cavities were coated recently for the first time. This contribution dis-cusses initial results from coating of twin axis cavities, RF testing and witness sample analysis with an overview of the current challenges towards high performance Nb3Sn coated twin axis cavities

New Approaches to Preventing, Diagnosing, and Treating Neonatal Sepsis

Karen Edmond and Anita Zaidi highlight new approaches that could reduce the burden of neonatal sepsis worldwide

Efficient solid-state dye-sensitized n-ZnO/D-358 dye/p-CuI solar cell

This paper describes the preparation and characterization of FTO/TiO2 dense layer/ZnO nanoporous layer/D-358 Dye/CuI hole collector/Cr-coated FTO and FTO/ZnO dense layer/ZnO nanoporous layer/D-358 Dye/CuI hole collector/Cr-coated FTO dye-sensitized solid-state solar cells. The variations of the solar cell parameters on the thickness of the TiO2 or ZnO dense layer are described. As the thickness (and hence the sheet resistance) of the TiO2 dense layer is increased, the conversion efficiency is gradually increased up to 2.6% at a sheet resistance of 370.0 Omega/square and beyond which it decreases. At this optimum thickness of the TiO2 dense layer, the best conversion efficiency is obtained when the thickness of the ZnO nanoporous layer is 15 mu m. Use of ZnO dense layer instead of TiO2 dense layer also shows the similar trend of variation of solar cell parameters as the thickness of the dense layer is increased. The best conversion efficiency of 3.2% is obtained when the sheet resistance of the ZnO dense layer is 2500 Omega/square and the thickness of the ZnO porous layer is 15 mu m. (C) 2013 Elsevier Ltd. All rights reserved