Pinning mechanism and engineering critical current density considerations in the design of MgB2superconducting coils

Influence of Amorphous Boron Grain Size, High Isostatic Pressure, Annealing Temperature, and Filling Density of Unreacted Material on Structure, Critical Parameters, n-Value, and Engineering Critical Current Density in MgB2 Wires

“…The critical parameters B irr , T c , and B c2 were identified for the criteria of 10%, 50%, and 90% resistance in the normal state [18]. The resistance in the normal state (R n ) for B = 0 T was determined at 40 K. However, magnetoresistance was determined in the range of the magnetic field from 0 T to 14 T. Transport critical current measurements were made using a measurement system with a bitter magnet up to 14 T at a temperature of 4.2 K. The critical current (I c ) was determined based on the 1 µm/cm criterion [29]. J ec was calculated from the relationship J ec = I c /S (S-wire cross-section) [29].…”

“…The transport measurements in the zero magnetic field show that the K-L samples have lower resistance (30% less) in the normal state than the A-C and F-H samples, indicating that nanoboron creates a larger number of connections between the grains than large boron and a mixture of boron. The results in Figure 11 for samples A-C (grain size of 1 µm) show that increasing the annealing temperature from 680 °C to 740 °C significantly increases the Jec by approximately 50% in the magnetic field range from 3 T to 6 T. The high annealing temperature in MgB2 wires with large boron grains seems to form mainly on surface pinning centers [29]. Jec was determined with the ratio Jec = Ic/S (S-wire cross-section) [29].…”

“…The results in Figure 11 for samples A-C (grain size of 1 µm) show that increasing the annealing temperature from 680 °C to 740 °C significantly increases the Jec by approximately 50% in the magnetic field range from 3 T to 6 T. The high annealing temperature in MgB2 wires with large boron grains seems to form mainly on surface pinning centers [29]. Jec was determined with the ratio Jec = Ic/S (S-wire cross-section) [29]. The transport results for sample F-H (mixture of boron grains-1 µm and 0.25 µm) show that increasing the annealing temperature from 680 °C to 700 °C increases Jec by one order of magnitude The results in Figure 11 for samples A-C (grain size of 1 µm) show that increasing the annealing temperature from 680 • C to 740 • C significantly increases the J ec by approximately 50% in the magnetic field range from 3 T to 6 T. The high annealing temperature in MgB 2 wires with large boron grains seems to form mainly on surface pinning centers [29].…”

“…Research has shown that nanoamorphous boron allows more connections between grains to be obtained, improves critical current density magnets. This value determines the critical current density (J c ) for the cross-section of superconducting wire and tape (e.g., diffusion barrier, wire sheath, heat matrix, and superconducting material) [28,29]. Depending on the device in which the superconducting coils are used, the J ec value is currently 20-50 A/mm 2 for magnetic resonance imaging (MRI) magnets, 20-50 A/mm 2 for large coils for detectors, and 100-200 A/mm 2 for laboratory solenoids [28].…”

“…B irr is dependent on high-field pinning centers that are created by structural defects, e.g., dislocations, stresses, strains, and substitutions of C for B [29][30][31][32]. MgB 2 material has an advantage of having a high critical temperature of 39 K [33].…”