Design and Optimization of Force-Reduced Superconducting Magnets Szabolcs Rembeczki* 74th 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

Why High Magnetic Fields ? Reaching higher magnetic fields would open new areas in various fields of research. Applications in: Condensed matter physics High energy physics Spin physics Materials chemistry Structural biology Power industry etc. Several targets for magnet technology: 30 T Superconducting high resolution NMR 60 T DC Hybrid magnet 100 T Long-pulse magnet Great demand on higher magnetic fields ! 11/29/2018 6:23 AM SESAPS

Current High Field Magnet Technology 45 T Hybrid Magnet at NHMFL Hybrid concept: Resistive insert + Superconducting outsert Layered structure Normal Conducting Water cooled Superconducting Liquid Helium cooled 11/29/2018 6:23 AM SESAPS

Operational Parameter Technical Superconductor Superconducting Materials Operational Parameter Technical Superconductor NbTi (ductile) Nb3Sn (brittle) HTS Toper(K) 4.2 20-77 Boper(T) < 10 < 25 >100 Promising HTS Materials: MgB2 Bi2212 YBCO Superconductors are pressure and strain sensitive ! H.J Schneider-Muntau et al.: Magnet Technology Beyond 50 T, Trans. Appl. Supercond., Vol.16, 2006 11/29/2018 6:23 AM SESAPS

Issue of Lorentz Forces in High Magnetic Field Magnets High 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 = B2 / 2μ0 (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 ! 11/29/2018 6:23 AM SESAPS

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.) 11/29/2018 6:23 AM SESAPS

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 11/29/2018 6:23 AM SESAPS

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 ! 11/29/2018 6:23 AM SESAPS

Questions or Comments? Thank You! 11/29/2018 6:23 AM SESAPS