A Field-Shaking System to Reduce the Screening Current-Induced Field in the 800-MHz HTS Insert of the MIT 1.3-GHz LTS/HTS NMR Magnet: A Small-Model Study.

In this paper, we present experimental results, of a small-model study, from which we plan to develop and apply a full-scale field-shaking system to reduce the screening current-induced field (SCF) in the 800-MHz HTS Insert (H800) of the MIT 1.3-GHz LTS/HTS NMR magnet (1.3G) currently under construction-the H800 is composed of 3 nested coils, each a stack of no-insulation (NI) REBCO double-pancakes. In 1.3G, H800 is the chief source of a large error field generated by its own SCF. To study the effectiveness of the field-shaking technique, we used two NI REBCO double-pancakes, one from Coil 2 (HCoil2) and one from Coil 3 (HCoil3) of the 3 H800 coils, and placed them in the bore of a 5-T/300-mm room-temperature bore low-temperature superconducting (LTS) background magnet. The background magnet is used not only to induce the SCF in the double-pancakes but also to reduce it by the field-shaking technique. For each run, we induced the SCF in the double-pancakes at an axial location where the external radial field Br > 0, then for the field-shaking, moved them to another location where the external axial field Bz ≫ BR . Due to the geometry of H800 and L500, top double-pancakes of 3 H800 coils will experience the considerable radial magnetic field perpendicular to the REBCO tape surface. To examine the effect of the field-shaking on the SCF, we tested each NI REBCO DP in the absence or presence of a radial field. In this paper, we report 77-K experimental results and analysis of the effect and a few significant remarks of the field-shaking.