Design and Optimization of ForceReduced Superconducting Magnets Szabolcs
Design and Optimization of Force-Reduced Superconducting Magnets Szabolcs Rembeczki* 74 th Annual Meeting of Southeastern Section of the American Physical Society (SESAPS) November 8 -10, 2007 Nashville, Tennessee *Florida Institute of Technology, Dept. of Physics and Space Sciences, Melbourne, Florida SESAPS
Why High Magnetic Fields ? Reaching higher magnetic fields would open new areas in various fields of research. Applications in: Several targets for magnet technology: • Condensed matter physics • High energy physics • Spin physics • 30 T Superconducting high resolution NMR • Materials chemistry • 60 T DC Hybrid magnet • Structural biology • 100 T Long-pulse magnet • Power industry etc. Great demand on higher magnetic fields ! 10/29/2020 SESAPS 2
Current High Field Magnet Technology 45 T Hybrid Magnet at NHMFL • Hybrid concept: Resistive insert + Superconducting outsert • Layered structure Normal Conducting Water cooled 10/29/2020 Superconducting Liquid Helium cooled SESAPS 3
Superconducting Materials Operational Parameter Technical Superconductor Promising HTS Materials: Nb. Ti (ductile) Nb 3 Sn (brittle) HTS (brittle) • Mg. B 2 Toper(K) 4. 2 20 -77 • YBCO Boper(T) < 10 < 25 >100 • Bi 2212 Superconductors are pressure and strain sensitive ! H. J Schneider-Muntau et al. : Magnet Technology Beyond 50 T, Trans. Appl. Supercond. , Vol. 16, 2006 10/29/2020 SESAPS 4
Issue of Lorentz Forces in High Magnetic Field Magnets High Stored Energy in the Magnet Large Lorentz Forces The main challenge of high field magnet development is the handling of the Lorentz forces. The pressure due to Lorentz force in a thin winding cylinder: Pm = Em = B 2 / 2μ 0 (Em – energy density) For B = 50 T field: Pm = 1 GPa (Yield tensile strength of maraging steel ~ 1400 -2100 MPa ) Lorentz force acting on SC coils: movement of the coil configuration can generate local frictional heat resulting in quench ! 10/29/2020 SESAPS 5
Force-Free Magnetic Field A magnetic field configuration B is force-free in a region if the j current(density) and B are parallel: FL = i l × B = 0 and j × B = 0 (G. J. Buck, Journal of Applied Physics, Vol. 36. ) 10/29/2020 SESAPS 6
Force-Reduced Superconducting Magnet Method of Force Reduction: • solenoid & toroid with windings of variably directed currents in N layers • geometrical parameters, conductor materials, and operational parameters needs to be optimized 10/29/2020 SESAPS 7
Concluding Remarks • State-of-the art high temperature superconductors allow realization of magnetic fields in access of 50 Tesla • However, the current carrying capacity of these conductors is compromised by stress and strain dependence of the materials • Reducing the forces acting in the winding configurations of high field magnets enables the application of such conductors • The main challenge of high field magnet development is the handling of the Lorentz forces • Force reduction is necessary in order to reach highest magnetic fields and to reduce the mass of the magnet support structure Force-reduced coils are the enabling technology for highest magnetic fields needed for basic research and applications ! 10/29/2020 SESAPS 8
Questions or Comments? Thank You! 10/29/2020 SESAPS 9
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