Influence of Inner Diameter and Height of Ring-Shaped REBaCuO Bulks on Trapped Field and Mechanical Stress During Field-Cooled Magnetization

In this paper, the trapped field B
_z
, thermal hoop stress σ
_θ
^cool
by cooling from 300 to 50 K, and electromagnetic hoop stress σ
_θ
^FCM
during field-cooled magnetization (FCM) from B
_app
= 6.3 and 9.4 T are investigated numerically for ring-shaped REBaCuO bulks with various inner diameters (I.D.) and heights (H) and reinforced by an Al alloy ring. For simplicity, an identical critical current density J
_c
(B), which is a typical value at 50 K, is assumed in the simulation. The B
_z
value at the center of the ring bulk changes depending on the I.D. and H values of the ring bulk, which results from the different distribution of the superconducting current. As a result, the total hoop stress σ
_θ
^total
(= σ
_θ
^cool
+ σ
_θ
^FCM
) also changes for each ring bulk and each B
_app
because of the variation of the σ
_θ
^cool
and σ
_θ
^FCM
values. The maximum σ
_θ
^total
value, which affects the bulk fracture at B
_app
= 9.4 T, increases with decreasing the height of ring bulk. These results can present guidelines for designing a trapped-field magnet using ring bulks.