Construction and Test Results of Coil 2 of a Three-Coil 800-MHz REBCO Insert for the 1.3-GHz High-Resolution NMR Magnet

This paper focuses on the construction and test results of Coil 2 that is a part of a trio of nested coils composing the REBCO 800-MHz insert. Upon its completion, the REBCO 800-MHz insert will be placed in the bore of a 500-MHz low-temperature superconducting nuclear magnetic resonance NMR magnet (L500) to form the MIT 1.3-GHz high-resolution NMR magnet. Coil 2 is a stack of 32 double-pancake (DP) coils wound with 6-mm-wide REBCO tape using the no-insulation technique. Each pancake is wound on a stainless steel inner supporting ring to prevent the collapsing of its crossover due to the external pressure exerted by the winding pack. Coil 2 will be constructed in the following sequence: 1) after winding, each DP will be individually tested in a bath of liquid nitrogen at atmospheric pressure to determine its current carrying capabilities; 2) DPs will be then assembled as a stack with interconnecting joints, and 3) as in Coil 1, each pancake will be overbanded with a stainless steel tape, this time to a thickness of 5 mm, thickness determined by a stress analysis previously performed. Finally, the fully assembled Coil 2 will be tested in liquid nitrogen at 77 K and then in liquid helium at 4.2 K. We present here details of the stress analysis leading to the sizing of the DP inner supporting stainless steel ring and of the overbanding thickness required. Test results include coil index, critical current, and charging time constant.