Engineering topics

Spradlin, Joshua

Publications and source records attributed to Spradlin, Joshua.

7 records

DOE OSTI2022

3rd harmonic magnetometry assessment of NbTiN-based SIS structures

In the quest for alternative superconducting materials to bring accelerator cavity performance beyond the bulk niobium (Nb) intrinsic limits, a promising concept proposes that superconductor-insulator-superconductor (SIS) thin film structures can delay magnetic flux penetration in accelerator cavities to higher fields [1]. NbTiN is a candidate superconductor for such structures. We have demonstrated high quality NbTiN and AlN deposited by reactive direct current magnetron sputtering (DCMS), both for individual layers and multilayers. Interface quality has been assessed for bi-layer stacks with various NbTiN and AlN thicknesses from 500 and 30 nm down to 3 and 1 nm. These SIS structures show continued sharp interfaces. The Hfp enhancement of the films was examined with 3rd harmonic magnetometry. The system was designed and built in an ongoing collaboration with CEA Saclay. It can measure 1? to 2? samples on a temperature controlled stage. This contribution presents the assessment of the first penetration field enhancement with 3rd harmonic magnetometry for standalone films and multilayer nanostructures.

Valente, Anne-Marie↗

DOE OSTI2018

Standardized beamline particulate characterization analysis: Initial application to CEBAF and LCLS-II cryomodule components

Despite continuously evolving efforts to minimize and manage the occurrence of particulates in operational SRF accelerator systems, the presence of electron field emission from contaminating particulates on SRF surfaces with high surface electric fields remains a consistent challenge. Jefferson Lab has recently initiated a standardized particulate sampling and characterization practice in order to gain more specific and systematic knowledge of the particulates actually present. It is expected that patterns emerging from such sampling will strengthen source attribution and guide improvement efforts. Initial samples were gathered from a cryomodule and adjoining warm girders that were removed from the CEBAF tunnel for reprocessing. The collection and analysis techniques were also used to characterize particulates on the inside of LCLS-II string components. Samples are transferred to clean industry-standard forensic GSR carbon tape spindles and examined via automated cleanroom SEM scanning for particle localization trends and sizing. The particulates are subsequently analyzed with EDS for elemental composition. A catalogue of found particle types is being accumulated. The methods used and results obtained from these initial applications will be presented.

Reece, Charles↗

DOE OSTI2013

NbTiN Based SIS Multilayer Structures for SRF Applications

For the past three decades, bulk niobium has been the material of choice for SRF cavities applications. RF cavity performance is now approaching the theoretical limit for bulk niobium. For further improvement of RF cavity performance for future accelerator projects, Superconductor Insulator - Superconductor (SIS) multilayer structures (as recently proposed by Alex Gurevich) present the theoretical prospect to reach RF performance beyond bulk Nb, using thinly layered higher-Tc superconductors with enhanced Hc1. Jefferson Lab (JLab) is pursuing this approach with the development of NbTiN and AlN based multilayer SIS structures. This paper presents the results on the characteristics of NbTiN films and the first RF measurements on NbTiN-based multilayer structure on thick Nb films.

Valente, Anne-marie↗

DOE OSTI2012

Structural Characterization of Nb Films Deposited by ECR Plasma Energetic Deposition on Crystalline Insulators

An energetic condensation thin film coating technique with an electron cyclotron resonance (ECR) induced plasma ion source is used to deposit Nb thin films on crystalline insulating substrates, such as a-plane and c-plane sapphire (Al2O3) and on magnesium oxide, MgO (100), (110) and (111). Heteroepitaxial Nb films were produced by ECR deposition with regulated substrate temperature. The residual resistance ratio (RRR) of about 1 micron thick films reach unprecedented values (350 - 450) on (11-20) sapphire substrates. The epitaxial relationship of Nb/crystalline substrate is found to be strongly influenced by the substrate bias voltage (adding to the initial Nb+ kinetic energy), the substrate crystalline orientation, and heating conditions. At low substrate temperature, the Nb films demonstrated non-epitaxial crystalline textures, revealed by XRD Pole Figure technique and Electron Backscattering Diffraction (EBSD). The texture might be caused by ?Volmer-Weber? growth mode, i.e. island growth, at low surface adatom mobility. This study shows that the film?s crystal structural character has great impact on its RRR/Tc value, which in turn is related to the electron-mean-free-path of radio-frequency superconductivity. The knowledge learned from this research sheds some light on how to coat low-defect density Nb thin films on SRF cavity-preferred metallic substrates, such as Cu.

Zhao, X.↗

DOE OSTI2012

Surface Preparation of Metallic Substrates for Quality SRF Thin Films

Surface Preparation of Metallic Substrates for Quality SRF Thin Films J. Spradlin*, A.-M. Valente-Feliciano, O. Trofimova, Thomas Jefferson National Accelerator Facility, Newport News, VA U.S.A. Surface preparation is an essential prerequisite for thin film depositions. Rough or chemically impure surfaces adversely affect the nature of the thin film. Understanding the properties of the substrate and how they influence the quality of the thin film is necessary to transfer thin film deposition technologies to SRF cavity applications. A substrate that is flat, has sufficient grain size, and is chemically pure is the ideal starting point for thin film depositions. A method for copper substrate preparation is reviewed for niobium thin film deposition that provides epitaxy on large and fine grain copper as well as single crystal copper. Preliminary data on niobium and aluminum substrate preparation will also be included. *Authored by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-06OR23177.

Spradlin, Joshua↗

DOE OSTI2012

SRF MULTILAYER STRUCTURES BASED ON NBTIN

For the past three decades, bulk niobium has been the material of choice for SRF cavities applications. In the recent years, RF cavities performances have approached the theoretical limit for bulk niobium. For further improvement of RF cavity performance for future accelerator projects, an interesting alternative has been recently proposed by Alex Gurevich with the Superconductor-Insulator-Superconductor multilayer approach, using the benefit of the higher critical field Hc2 of higher-Tc superconductors without being limited with their lower Hc1. JLab is pursuing this approach with the development of multilayer structures based on NbTiN via magnetron sputtering and High Power Impulse Magnetron Sputtering (HiPIMS). Insulators such as, AlN, Al2O3 and MgO are being investigated as candidates for the insulator layers. This paper present the preliminary results on the characteristics of NbTiN and insulator layers and a first attempt of a NbTiN-based multilayer structure on bulk Nb and thick Nb films.

Valente, Anne-Marie↗

DOE OSTI2012

Structural Properties of Niobium Thin Films Deposited on Metallic Substrates by ECR

Particle accelerator technologies rely on SRF cavities to create the accelerating gradient for beam lines. Solid niobium cavities are widely employed throughout the community despite high material, fabrication, and operation cost. New thin film technologies are being explored for the suitability of niobium coatings for accelerating cavities. Thin layers of high-quality niobium would be deposited on a base material that has lower material and fabrication cost. Copper is a strong candidate for the cavity base due to availability, cost, machinability, and potentially improved performance characteristics of the niobium SRF surface. Initial results of TEM, EBSD and XRD analyses of niobium thin films grown on copper substrates under controlled conditions are presented to demonstrate the feasibility of the technology and establish lower limits of performance characteristics. Correlation of RRR data with the structure of niobium thin films will demonstrate the importance of thin film structural quality. *Authored by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-06OR23177.

Spradlin, Joshua↗