A Field-Shaking System to Eliminate 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 results, experimental and analytical, of a small-model study, from which we plan to develop and ap-ply a full-scale field-shaking system to minimize or even elim-inate 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 dou-ble-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 use two NI REBCO double-pancakes, one from 2 coils (HCoil2 and HCoil3) of the 3 H800 coils, and place them in the bore of a 5-T/300-mm room-temperature bore external magnet. The external magnet is used not only to induce SCF in the double-pancakes but also elimi-nate it by the field-shaking. For each run, we induce SCF in the double-pancake at an axial location where the external radial field Br > 0, then for the field-shaking, move to another location where the external axial field Bz >> BR. To examine if other SCF eliminating techniques, e.g., the current-sweep-reversal (CSR) method, is applicable to H800 even when L500 and H800 are series-connected, we perform similar sequences of test for other combinations of the double-pancake axial locations. In this paper, we report 77-K experimental results, develop an analy-sis that satisfactorily explains the results, and apply the analy-sis to design a field-shaking system for 1.3G at full operation.