Fibrous structure and critical current density of MgB2 superconducting wire

Uchiyama, Daisuke; Mizuno, K.; Akao, Takashi; Maeda, Masafumi; Kawakami, Takateru; Kobayashi, Hirokazu; Kubota, Yoshihiro; Yasohama, K.

doi:10.1016/j.cryogenics.2007.03.003

Cited by 16 publications

(16 citation statements)

References 16 publications

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“…Transport measurements of J ct and magnetic measurements of J cm as functions of B and T were made as described above. As shown in Figure 1(a) the MgB 2 core of the CTFF strand is a solid cylinder (albeit with a longitudinal fibrous macrostructure [6][8]), whereas the superconducting core of the IMD strand is a hollow cylinder of MgB 2 [7],…”

Section: Transport and Magnetic Critical Current Densities J Ct And J CMmentioning

confidence: 99%

“…Attention has also been paid to strand fabrication techniques, particularly Hyper Tech Research's (HTR) "continuous tube filling and forming" (CTFF) process in which the precursor powder mixture is continuously dispensed onto a strip of metal prior to its being formed into a tube [4], and the "internal Mg diffusion" (IMD) process, which starts off with a Mg rod imbedded axially in a B-filled tube and continues with wire forming and final heat treatment, HT [5]. Compared to the CTFF and conventional powder-in-tube (PIT) processes which yield a system of randomly connected MgB 2 fibers [6] IMD produces a dense MgB 2 layer structure with better longitudinal connectivity [7].…”

Section: Introductionmentioning

confidence: 99%

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Critical current densities andn-values of MgB₂strands over a wide range of temperatures and fields

Yang²,

Susner³

et al. 2011

Supercond. Sci. Technol.

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Transport measurements of critical current density, J ct , in monocore powder-in-tube MgB 2 strands have been carried out at temperatures, T, of from 4.2 K to 40 K, and in transverse fields, B, of up to 14 T. Processing methods used were conventional continuous-tube-forming-filling (CTFF) and internal-magnesium-diffusion (IMD).Strands with several powder compositions were measured, including binary (undoped) MgB 2 , 2% carbon doped MgB 2 , and 3% carbon doped MgB 2 . Magnetization loops (M-B) were also measured, and magnetic critical current density, J cm , values extracted from them. The transport, J ct (B) and magnetic, J cm (B), critical current densities were compared.Also studied was the influence of doping on the resistively measured irreversibility field, B irr and upper critical field B c2 . Critical current densities, J ct , and n-values were extracted from transport measurements and were found to be universally related (for all B and T) according to n∝ J ct m in which m = 0.52 ± 0.11. Likewise n was found to be related to B according to n ∝ B -p with a T-dependent p in the range of about 0.08~0.21. Further analysis of the field (B) and temperature (T) dependencies of n-value resulted in an expression that enabled n(B,T), for all B and T, to be estimated for a given strand based on the results of transport J ct (B) measurements made at one arbitrarily chosen temperature. Symbols B Magnetic field strength B irrResistively determined irreversibility field B irr,trans Apparent irreversibility field for magnetically induced current paths which must always include a portion transverse to the strand axis B c2Upper critical field B 0 (t)Temperature-dependent field-normalization quotient in the exponential form of J c (B,t) -see below B 00 Zero-temperature value of B 0 (t) CTFF Continuous tube forming/filling (process for strand fabrication) d 0 Inner diameter of the Nb chemical barrier (both CTFF and IMD strands) d i Inner diameter of the annular MgB 2 reaction layer (IMD strands) ∆M Full height of the magnetization loop normalized to the actual SC volume F p Bulk pinning force density F p,max Maximum value of F p vs B or B/B irr IMD Internal magnesium diffusion (process for strand fabrication) J c Abbreviation for the words "critical current density" J ct Transport-measured critical current density J cm Magnetically measured critical current density J cte Transport critical current density found by normalized I ct to the whole area inside the Nb chemical barrier J c2Critical current density transverse to the strand axis (magnetically induced) J c (B,t) Field-and temperature dependent J c J ct (B,t) Transport-measured value of field-and temperature dependent J c J c0 (t)Fitted zero-field temperature-dependent J c J ct0 (t)Fitted zero-field temperature-dependent J c based on transport measured field and temperature dependent J c equation J c00Fitted value of J c at zero field and zero temperature

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Section: Transport and Magnetic Critical Current Densities J Ct And J CMmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Critical current densities andn-values of MgB₂strands over a wide range of temperatures and fields

Yang²,

Susner³

et al. 2011

Supercond. Sci. Technol.

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“…Connectivity manifests itself at two levels: (i) between the individual MgB 2 grains, (ii) between aggregates (fibers, see below) of even well connected polycrystalline grains. With regard to in situ processed PIT MgB 2 strands, it has been noted [4] [43] that the drawing of the mixed powders leads eventually to a fibrous macrostructure. The term "macrostructure" is herein used to indicate that the fiber dimensions (typically 27 µm x 2.5 µm) are very much larger than the typical grain size (≈ 50 nm).…”

Section: Introductionmentioning

confidence: 99%

Drawing induced texture and the evolution of superconductive properties with heat treatment time in powder-in-tubein situprocessed MgB₂strands

Susner

Daniels

Sumption

et al. 2012

Supercond. Sci. Technol.

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Monocore powder-in-tube MgB 2 precursor strands were cold-drawn and heat- This effect is attributed to the fibrous macrostructure and its accompanying anisotropic connectivity. Magnetic measurements with the field directed along the strand axis yielded a critical density, J cm ┴ (B), for current flowing transversely to the strand axis that was less than and dropped off more rapidly than J ct (B). In the conventional magnetic measurement, the loop currents that support the magnetization are restricted by the lower of J ct (B) and J cm  (B). In the present case the latter, leading to the premature dropoff of the measured J cm (B) compared to J ct (B) with increasing field. This result is supported byKramer plots of the J cm  (B) and J ct (B) data which lead to an irreversibility field for transverse current that is very much less than the usual transport-measured longitudinal one, B irr,t .

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“…The formation of the textured structure in superconducting wires and tapes is important because it allows a significant increase in the critical parameters, e.g., transport critical current density ( J c ) and irreversible ( B irr ) as well as upper ( B c2 ) magnetic fields. Uchiyama et al [ 1 ] showed that cold rolling a square wire using a two-axial grooved roller could create a textured fiber structure with a fiber diameter of 15 µm for a 1-mm diameter wire before annealing. However, annealing above 630 °C would lead to the disappearance of the textured fiber structure, and a large number of sizable voids would appear [ 1 ].…”

Section: Introductionmentioning

confidence: 99%

High Critical Current Density in the Textured Nanofiber Structure in Multifilament MgB2 Wires Made by the Powder-In-Tube (PIT) Technique

et al. 2022

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We show that the structure of multifilament MgB2 wires made by the powder-in-tube (PIT) method can be texturized by annealing the structure under high isostatic pressure. Our results show that we obtained continuous fibers with a uniform diameter of 250 nm in all 36 filaments, a small grain size of approximately 50 nm and a high density of the superconducting material. These results contribute to a significant improvement in the critical current density in high magnetic fields, e.g., 100 A/mm2 at 14 T and 4.2 K.

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Fibrous structure and critical current density of MgB2 superconducting wire

Cited by 16 publications

References 16 publications

Critical current densities andn-values of MgB₂strands over a wide range of temperatures and fields

Critical current densities andn-values of MgB₂strands over a wide range of temperatures and fields

Drawing induced texture and the evolution of superconductive properties with heat treatment time in powder-in-tubein situprocessed MgB₂strands

High Critical Current Density in the Textured Nanofiber Structure in Multifilament MgB2 Wires Made by the Powder-In-Tube (PIT) Technique

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Fibrous structure and critical current density of MgB2 superconducting wire

Cited by 16 publications

References 16 publications

Critical current densities andn-values of MgB2strands over a wide range of temperatures and fields

Critical current densities andn-values of MgB2strands over a wide range of temperatures and fields

Drawing induced texture and the evolution of superconductive properties with heat treatment time in powder-in-tubein situprocessed MgB2strands

High Critical Current Density in the Textured Nanofiber Structure in Multifilament MgB2 Wires Made by the Powder-In-Tube (PIT) Technique

Contact Info

Product

Resources

About

Critical current densities andn-values of MgB₂strands over a wide range of temperatures and fields

Critical current densities andn-values of MgB₂strands over a wide range of temperatures and fields

Drawing induced texture and the evolution of superconductive properties with heat treatment time in powder-in-tubein situprocessed MgB₂strands