A High-Resolution 1.3-GHz/54-mm LTS/HTS NMR Magnet

The no-insulation (NI) winding technique drastically enhances the thermal stability of REBa2Cu30y (REBCO) coils. Even if a larger current than a critical current carried in NI REBCO pancake coils, the coils would not burn out. So far, many NI REBCO pancake coils showed a "self-protecting" characteristic in experiments. However, most of these experiments have been done under a low magnetic field or cooled by liquid nitrogen. Under these conditions, a huge electromagnetic force does not occur after an NI REBCO pancake coil transitions into a normal state.Recently, the NI winding technique has been applied to high field magnets, such as NMR and accelerators. Under a high magnetic field, a huge hoop stress are generated after one NI REBCO pancake coil constituting a high field magnet by stacking reaches to quench. The huge hoop stress causes the delamination of REBCO coated conductors. That is, the quench protection condition of high field NI REBCO magnets is decided according to the mechanical condition, even though the magnets show a high thermal stability. In this paper, 3 simulation models for NI REBCO pancake coils are compared, and then the mechanical condition is discussed for a quench protection through an electromagnetic, thermal, and mechanical simulation of multistacked NI REBCO pancake coils for high field generation.

“…A field of 31.5 T is a world record of DC magnetic field [1]. MIT, RIKEN, and other institutes have been developing NMR REBCO magnets generating a magentic field higher than 30 T [2].…”

Section: Introductionmentioning

confidence: 99%

Electromagnetic, Thermal, and Mechanical Quench Simulation of NI REBCO Pancake Coils for High Magnetic Field Generation

Noguchi

2019

“…On the other hand, when r ct > 1, r r is linearly proportional to r ct , i.e., r r is dominated by the turn-to-turn contact surface. Therefore, when the contact resistance is enough high, such as 70 µΩ·cm 2 [3], the coil-radial contact resistivity can be used as the turn-to-turn contact surface resistivity.…”

Section: B Coil-radial Contact Resistivitymentioning

confidence: 99%

“…This technique can be applied to REBCO pancake coils for the use of NMR [3], MRI, and accelerator applications. The NI winding technique enhances stability and current density simultaneously; when a local hotspot appears in an NI REBCO coil, the transport current can avoid it and flows directly into the adjacent turns.…”

Section: Introductionmentioning

confidence: 99%

“…So far, to confirm the effectiveness of the NI winding technique, some current flow simulations in a pancake coil have been performed using the simple equivalent electrical circuit model [5], [6] or the partial element equivalent circuit (PEEC) model [7]. Through these simulations [4]- [6] and experiments [1]- [3], [7] it was Automatically generated dates of receipt and acceptance will be placed here; authors do not produce these dates. This work was supported in part by the Grant-in-Aid for Scientific Research (A) (Grant Number 26249036).…”

Section: Introductionmentioning

confidence: 99%

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Investigation of Current Flow Between Turns of NI REBCO Pancake Coil by 2-D Finite-Element Method

Noguchi

Monma

Igarashi

et al. 2016

Abstract-TheNo-Insulation (NI) winding technique for NI REBCO pancake coil is expected to improve the dynamic and thermal stability and to enhance the current density. The investigations of the electromagnetic and thermal behaviors are important for the development of NI REBCO coils. Many stability investigations of the NI REBCO coil itself have been carried out by experiments and simulations. However, the detailed behavior of the bypass current between turns has been not shown yet. Although the contact resistivity was obtained through the priori experiment, it included the resistivity of not only contact surface but also the components, i.e., the copper stabilizer and the Hastelloy substrate, of REBCO tape. To investigate the detailed bypass current behavior in this paper, the true contact surface resistivity is taken into account in the simulation. The bypass current on the cross section of NI REBCO tape is simulated using the 2-D FEM. From the simulation results, the influence of the coil-radial resistivity between turns on the turn-to-turn contact surface resistivity is clarified. In addition, the heat loss is also reported, and a simple equivalent circuit of the turn-to-turn contact is proposed.

“…A general overview of the magnet system has been published elsewhere [1]. To date, Coil 1 the innermost coil has been fabricated and fully tested with and without its overbanding.…”

Section: Introductionmentioning

confidence: 99%

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

Bascuñán

Michael

Hahn

et al. 2017

Self Cite

This paper focuses on the construction and test results of Coil 2 that is 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 (LTS) 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 (NI) 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, charging time constant.