Design Optimization of a Hybrid Trapped Field Magnet Lens (HTFML)

The concept of a hybrid trapped field magnet lens (HTFML) was recently proposed by the authors, which consists of a trapped field magnet (TFM) cylinder exploiting the “vortex pinning effect,” combined with a superconducting bulk magnetic lens exploiting the “diamagnetic shielding effect.” This HTFML can generate, within its bore, a magnetic field higher than the applied magnetic field, even after external field decreases to zero. In this paper, a design optimization of the inner GdBaCuO magnetic lens within the GdBaCuO TFM cylinder was carried out using numerical simulations based on the finite-element method, in order to maximize the concentrated magnetic field. The HTFML with an optimized shape and size achieved a concentrated magnetic field of B
_c
= 5.6 and 12.8 T at the center of the lens for applied magnetic fields of B
_app
= 3 and 10 T, respectively. A maximum tensile stress of +135 MPa exists in the outer GdBaCuO TFM cylinder during the magnetizing process for B
_app
= 10 T, which exceeds the fracture strength of the bulk. This result suggests that mechanical reinforcement is necessary to avoid mechanical fracture under such high magnetic field conditions.