HTS Technology for High-Field Persistent-Current Magnet Systems

Title data

Oomen, Marijn ; Arndt, Tabea ; Hasselt, Peter van ; Frank, Michael ; Denneler, Stefan ; Glosse, Philipp ; Stöcker, Thomas ; Kauffmann-Weiss, Sandra ; Häßler, Wolfgang:
HTS Technology for High-Field Persistent-Current Magnet Systems.
2016
Event: Applied Superconductivity Conference 2016, ASC2016 , 04.-09.09.2016 , Denver, Colorado, USA.
(Conference item: Conference , Speech )

Project information

Abstract in another language

Nuclear-magnetic resonance (NMR) and magnetic-resonance-imaging (MRI) systems are based on superconducting persistent-current magnets, usually wound with Nb-based low-Tc superconductors cooled with liquid Helium (LHe). Use of magnesium diboride (MgB2), or the cuprate high-temperature superconductors (HTS) like Y- or Bi-compounds, enables higher field strengths or operating temperatures, allowing simpler cooling systems without large volumes of LHe. The sustainable use of the precious resource Helium becomes increasingly important. Dry magnet systems will contribute to that. In addition, using HTS the quench stability can be increased. Technical challenges in using HTS are: persistent-current operation, slow quench propagation, ride-through of an interruption in cooling power, screening currents in the HTS wire / tape, conductor cost and uniform cooling of a large system. In addition to the economy of scale, the conductor cost may be greatly decreased by using MgB2 in combination with a simple scalable production process, like aerosol deposition, which we are developing in-house. MgB2 powder is dispersed in a gas stream and impacts a substrate at high velocity, the kinetic energy enables compression and bonding even at room temperature. The process is outlined and promising recent results are presented. In order to demonstrate and validate solutions for persistent operation, screening currents and uniform cooling, we have built and tested an HTS demonstrator magnet system. The system uses 470 m of ReBCO tape for a 1.3 T design field in a 170 mm warm bore. The coils are cooled to 25 K by a single-stage GM refrigerator in a simple vacuum vessel. We discuss the specification, system design, the manufacturing technique, system assembly and sensors. The system has been successfully tested up to 70 A operating current. Stability of the persistent current measured over a long time shows an overall system resistance below 10-11 Ohm, low enough to fulfill the MRI field-stability criterion in a full-scale system. This semi-portable “desk-top” magnet system can be demonstrated virtually anywhere. We believe, when the challenges are addressed, MgB2 and ReBCO are viable materials for future NMR and MRI (potentially cryogen-free) magnet systems and may also open further opportunities for superconducting magnet applications.