Intensive research has been directed at MgB2 since its discovery in 2001, focusing first on the material properties and conductor development and recently also on coil demonstrations. The relatively cheap and easy fabrication makes MgB2 a tempting material for superconducting applications. It can also be operated in the vicinity of 20 K, at which the commercial LTS materials are still in the normal state. However, commercial breakthrough requires practical applications and demonstrations. Therefore, we built a solenoidal react-and-wind MgB2 coil consisting of 46 m of commercially available MgB2 /Ni/Fe/Cu tape manufactured by Columbus Superconductors. We tested the coil in a cryogen-free environment and measured the effect of repeated cooldowns and current ramp rate on the coil critical current. Also, temperature homogeneity in the winding was studied. Based on the test results we point out features which should be checked when cryogen-free magnet systems are designed or their performance is discussed. For example, the coil critical current and n value can depend notably on the current ramp rate.

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Superconducting magnets operate at low temperatures, and therefore, even small heat pulses can ruin their stable operation. For example, resistive joints or changes in the operation current generate heat which must be extracted to prevent a quench. In impregnated magnets, the transverse thermal conductivity inside the coil has a vital influence on the heat extraction, and it dominates the 3D quench propagation. In this study, the transverse heat conductivity is measured from the cross-section of a small epoxy impregnated MgB2 coil at temperatures between 10 and 35 K. Finally, the results are analysed and compared with the results of a computational model based on heat conduction equation solved with the finite element method. The results show that effective thermal conductivity is over two orders of magnitude higher in the parallel direction with conductor axis compared to the perpendicular direction. The measured effective thermal conductivities at 20 K parallel to the broad tape face and perpendicular to the broad tape face were 1.55 W/mK and 0.31 W/mK, respectively. The fill factor of the measured coil was 60.5% for the whole conductor.