Public Abstract

DE-SC0011631: Superconducting joints between (RE)Ba2Cu3O7- coated conductors via electric field assisted processing

Award Status: Inactive

Institution: North Carolina State University, Raleigh, NC
UEI: U3NVH931QJJ3
DUNS: 042092122

Most Recent Award Date: 02/24/2016
Number of Support Periods: 2
PM: Marken, Kenneth

Current Budget Period: 04/01/2015 - 03/31/2017
Current Project Period: 05/01/2014 - 03/31/2017
PI: Schwartz, Justin

Supplement Budget Period: N/A

Public Abstract

Superconducting Joints Between (RE)Ba₂Cu₃O_7-x Coated Conductors via Electric Field Assisted Processing Principal Investigator: Justin Schwartz, North Carolina State University High temperature superconductors (HTS) are expected to be the primary high field superconductors for future high-energy physics (HEP) magnets. In the 26 years since their discoveries, significant progress has been made in HTS technology and high field magnet projects are moving forward. Of the HTS materials discovered, Bi₂Sr₂CaCu₂O_x–based wires and (RE)Ba₂Cu₃O_7-x (REBCO) coated conductors have the greatest potential for high magnetic field HEP magnets, with REBCO having a distinct advantage in mechanical properties and electromechanical behavior. Although long length manufacturing of REBCO tapes has made progress, routine lengths are still only 100-300 m. As large, high field magnets for HEP applications require km lengths of REBCO conductor, superconducting joints are needed to piece together lengths of conductor. Furthermore, even if improvements in the manufacturing of REBCO conductors improves such that sufficiently long lengths of homogeneous conductor become available, superconducting joints offer magnet designers the option of grading the conductor within a large magnet. It is also important to recognize that large superconducting magnets for HEP applications often require cables because large inductances cause severe problems during the charging and discharging of high ampere-turn devices; high inductance can be particularly challenging for quench protection. The batch length of REBCO conductor available limits the length of cable that can be manufactured, thus the availability of superconducting joints may be enabling for large, cable-wound magnets. The development of superconducting joints for complex cables, however, is more challenging than the development of tape-to-tape joints. The limited space available, the need to maintain high engineering critical current density (J_E) and the complexity of the geometries dictate that a joining technique be simple, reliable and readily reproducible. We propose to use electric field assisted processing (EFP) to develop superconducting joints between REBCO conductors. In experiments with other materials systems, EFP has been shown to inhibit grain growth, clean the surface of grains to encourage intergranular contacts, improve the quality of interparticle bonds and allow for lower temperature atomic diffusion and defect motion. EFP has also been shown to prevent the formation of new phases and maintain anisotropy of the material being processed. EFP can be performed at or near room temperature, which aids in preventing oxygen loss in oxides. Thus, EFP is a particularly promising pathway to REBCO-REBCO superconducting joints. Furthermore, a recent preliminary experiment at NC State University has shown that EFP can cause diffusion bonding at a YBCO-YBCO interface and create a mechanically sound bond. Thus, we propose to build on this initial proof-of-concept experiment to investigate systematically EFP as an approach to creating high performance REBCO-REBCO superconducting joints. The objective of this work is to develop a pathway to joining REBCO coated-conductors that is directly scalable to cables. In particular, a primary objective is to form superconducting joints with high J_E using a simple, localized approach based upon EFP that does not require high temperatures. Additionally, we will develop an understanding of the relationships between EFP-microstructure-properties, including electrical, magnetic and mechanical behavior. The primary focus will be on high field transport and electromechanical behavior. By developing an understanding of the mechanisms and factors pertinent to improving behavior, we will subsequently improve the specific details of the EFP approach to further improve joint characteristics. This research will result in a dense superconducting joint which facilitates magnets requiring much longer lengths than the current batch-length limit to be built and operated in persistent mode, tape-to-tape and cable-to-cable connections, and magnet design flexibility through conductor grading. Collaborative experiment: none.

Superconducting Joints Between (RE)Ba₂Cu₃O_7-x Coated Conductors via Electric Field Assisted Processing

Principal Investigator: Justin Schwartz, North Carolina State University

High temperature superconductors (HTS) are expected to be the primary high field superconductors for future high-energy physics (HEP) magnets. In the 26 years since their discoveries, significant progress has been made in HTS technology and high field magnet projects are moving forward. Of the HTS materials discovered, Bi₂Sr₂CaCu₂O_x–based wires and (RE)Ba₂Cu₃O_7-x (REBCO) coated conductors have the greatest potential for high magnetic field HEP magnets, with REBCO having a distinct advantage in mechanical properties and electromechanical behavior.

Although long length manufacturing of REBCO tapes has made progress, routine lengths are still only 100-300 m. As large, high field magnets for HEP applications require km lengths of REBCO conductor, superconducting joints are needed to piece together lengths of conductor. Furthermore, even if improvements in the manufacturing of REBCO conductors improves such that sufficiently long lengths of homogeneous conductor become available, superconducting joints offer magnet designers the option of grading the conductor within a large magnet. It is also important to recognize that large superconducting magnets for HEP applications often require cables because large inductances cause severe problems during the charging and discharging of high ampere-turn devices; high inductance can be particularly challenging for quench protection. The batch length of REBCO conductor available limits the length of cable that can be manufactured, thus the availability of superconducting joints may be enabling for large, cable-wound magnets. The development of superconducting joints for complex cables, however, is more challenging than the development of tape-to-tape joints. The limited space available, the need to maintain high engineering critical current density (J_E) and the complexity of the geometries dictate that a joining technique be simple, reliable and readily reproducible.

We propose to use electric field assisted processing (EFP) to develop superconducting joints between REBCO conductors. In experiments with other materials systems, EFP has been shown to inhibit grain growth, clean the surface of grains to encourage intergranular contacts, improve the quality of interparticle bonds and allow for lower temperature atomic diffusion and defect motion. EFP has also been shown to prevent the formation of new phases and maintain anisotropy of the material being processed. EFP can be performed at or near room temperature, which aids in preventing oxygen loss in oxides. Thus, EFP is a particularly promising pathway to REBCO-REBCO superconducting joints. Furthermore, a recent preliminary experiment at NC State University has shown that EFP can cause diffusion bonding at a YBCO-YBCO interface and create a mechanically sound bond. Thus, we propose to build on this initial proof-of-concept experiment to investigate systematically EFP as an approach to creating high performance REBCO-REBCO superconducting joints.

The objective of this work is to develop a pathway to joining REBCO coated-conductors that is directly scalable to cables. In particular, a primary objective is to form superconducting joints with high J_E using a simple, localized approach based upon EFP that does not require high temperatures. Additionally, we will develop an understanding of the relationships between EFP-microstructure-properties, including electrical, magnetic and mechanical behavior. The primary focus will be on high field transport and electromechanical behavior. By developing an understanding of the mechanisms and factors pertinent to improving behavior, we will subsequently improve the specific details of the EFP approach to further improve joint characteristics. This research will result in a dense superconducting joint which facilitates magnets requiring much longer lengths than the current batch-length limit to be built and operated in persistent mode, tape-to-tape and cable-to-cable connections, and magnet design flexibility through conductor grading.

Collaborative experiment: none.