A new MgB₂ bulk ring fabrication technique for use in magnetic shielding or bench-top NMR systems

Abstract

We report a new methodology in bulk MgB2 ring production for use in small-scale magnetic shielding or bench-top NMR systems. This process is a modified field-assisted sintering technique (mFAST) which enables direct formation of the rings without the need for machining or additives into the precursor powder. The shielding and trapped field capabilities of three mFAST MgB2 rings were determined using zero-field- (ZFC) and field-cooled (FC) magnetic experiments. Individual bulks trap magnetic fields up to 1.24T at 20K comparable to the highest published data for a ring sample. It is anticipated that for many applications, multiple rings will be stacked to form the required experimental structure. We find for the three ring stack a trapped field of 2.04T and a maximum shielded field of 1.74T at 20K. The major factor limiting performance at low temperatures are flux jumps which cause rapid loss of the trapped field or shielding capability. Preliminary studies of magnetic field ramp rate dependence on flux jumps were conducted illustrating that even at very slow ramp rates (0.007 T/min) they remain a significant issue. Despite this concern, we conclude that mFAST represents an exciting new fabrication methodology for bulk MgB2 rings.

Avalanche dynamics of magnetic flux in the Nb-Ti superconducting ring

“…When the possibility of easy entry and filling of the cavity with magnetic flux arises, the critical state of the doubly connected superconductors is less resistant to thermomagnetic disturbances [9]. Ring-shaped bulk superconductors have a wide range of practical applications (magnetic resonance imaging systems, etc) [18][19][20][21][22]. The stability threshold of the critical state of such superconductors, in accordance with theoretical concepts [23], is significantly lower.…”

The Influence of Preparation Temperature on the Different Facets of Bulk MgB2 Superconductors

“…It is also speculated that, according to the raw materials of MgB 2 superconducting bulks, there are no toxic elements in their ingredients, which is relatively safe and conducive to environmental protection [ 10 ]. All these characteristics make MgB 2 a promising superconducting material for NMR/MRI magnets [ 14 ], motors/generators [ 15 ], etc. Most of these applications need a strong trapped magnetic field that is proportional to the critical current density, J C , and sample size according to the Bean model [ 16 ].…”

A Comparative Study of Experimental and Simulated Trapped Magnetic Field of MgB2 Bulks Prepared by the Magnesium Vapor Transport Process

“…Several processes have been developed for MgB2 bulk fabrication, including the in-situ method [4], [6]- [9], in which a mixed powder of magnesium and boron reacts; the high-pressure synthesis method [10]- [16]; the diffusion method using liquid magnesium [17], [18]; and liquid phase assisted sintering [19]. In the conventional in-situ method, the packing factor of MgB2 is as low as around 50%, since the density of reacted MgB2 is higher than the density of the Mg/B precursor powders [6], [7].…”