Atom probe tomography analysis of Nb3Sn superconducting wires for fusion reactor and particle accelerator applications
<p>First discovered in 1954, Nb<sub>3</sub>Sn is a low temperature superconductor, which has had a resurgence in interest in recent years. Multiple projects, such as the Hi-Lumi upgrade to the Large Hadron Collider and the fusion reactor ITER have used Nb<sub>3</sub>Sn...
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| Other Authors: | |
| Format: | Thesis |
| Language: | English |
| Published: |
2023
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| _version_ | 1811140376368513024 |
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| author | Wheatley, L |
| author2 | Grovenor, C |
| author_facet | Grovenor, C Wheatley, L |
| author_sort | Wheatley, L |
| collection | OXFORD |
| description | <p>First discovered in 1954, Nb<sub>3</sub>Sn is a low temperature superconductor, which has had a resurgence in interest in recent years. Multiple projects, such as the Hi-Lumi upgrade to the Large Hadron Collider and the fusion reactor ITER have used Nb<sub>3</sub>Sn superconducting magnets, and there are plans to use improved Nb<sub>3</sub>Sn wires for a Future Circular Collider (FCC). Nb<sub>3</sub>Sn is the second most commercially available superconductor after NbTi, which revolutionised the medical sector making MRI machines possible. However, NbTi has a maximum field of 14 T, compared to the higher maximum field of 28 T for Nb<sub>3</sub>Sn.</p>
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<p>The FCC target is 1500 Amm<sup>-2</sup> at 16 T, much more challenging than previous applications of Nb<sub>3</sub>Sn. To reach this target fluxons, which are 3 - 4 nm in radius in Nb<sub>3</sub>Sn, need to be trapped at defects within the Nb<sub>3</sub>Sn microstructure. Historically, grain refinement has been the main method of increasing the J<sub>c</sub> by maximising the grain boundary area which can pin fluxons. Commercial Nb<sub>3</sub>Sn wires have a grain size of ≈ 100 nm, however, it is difficult to reduce the grain size further and still produce a homogeneous Nb<sub>3</sub>Sn layer with favourable superconducting properties. To increase J<sub>c</sub> to reach the FCC target, artificial pinning centres (APCs), on the scale of the fluxons are required.</p>
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<P>Considering the importance of the nanoscale structure on the superconducting properties of Nb<sub>3</sub>Sn, little is known about nanoscale chemical segregation within Nb<sub>3</sub>Sn. In this work, Atom Probe Tomography (APT) has been used to understand the nanoscale structure of two different types of Nb<sub>3</sub>Sn wires, restacked-rod-processed (RRP®) and rod-in-tube (RIT) type wires. The first set of results focuses on a commercial RRP® wire doped with Ti and a comparative RRP® wire, irradiated at a neutron fluence of 2.82 x 10<sup>22</sup>m<sup>-2</sup> in the TRIGA II reactor. The inter-grain compositions, intra-grain compositions and any additional features such as dislocations were studied. Both RRP® samples had intra-grain compositions which were formed of two different, non-equilibrium compositions, one higher in Nb and one lower in Nb. The irradiated RRP® sample had a lower volume of high Nb compared to the as-received sample, this suggests that irradiation induced diffusion has occurred due to the excess of vacancies produced during neutron irradiation.</p>
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<p>The second set of results focuses on a RIT test wire which reached the high J<sub>c</sub> requirement for the FCC. The pinning curve from this wire suggested the presence of APCs, despite no intentional source of oxygen added to the wire, to produce APCs through internal oxidation. An Electron probe micro-analyser (EPMA) and APT have been used to determine the oxygen concentration in the unreacted and reacted Nb-4Ta-1Hf (at%) alloy, with evidence of HfO<sub>2</sub> nanoparticles in the reacted Nb-4Ta-1Hf alloy. In a similar way to the RRP® samples, the intra-grain and inter-grain compositions of the Nb<sub>3</sub>Sn layer have been measured, and the size and number density of HfO<sub>2</sub> APCs have been calculated. Additional features have been analysed, such as a residual Nb<sub>6</sub>Sn<sub>5</sub> layer at the edge of the Nb<sub>3</sub>Sn region and residual Cu rich phases trapped within the Nb<sub>3</sub>Sn layer. Evidence of HfO<sub>2</sub> in the reacted Nb-4Ta-1Hf alloy and the Nb<sub>6</sub>Sn<sub>5</sub> layer shows HfO<sub>2</sub> nanoparticles were formed prior to Nb<sub>3</sub>Sn and that the HfO<sub>2</sub> nanoparticles may have acted as Zener pinning sites to reduce the grain size of the Nb<sub>3</sub>Sn. Nb<sub>6</sub>Sn<sub>5</sub> has been shown to have a higher Cu solubility than Nb<sub>3</sub>Sn, perhaps explaining the trapped regions of Cu rich phases within the Nb<sub>3</sub>Sn.</p>
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<p>For future Nb<sub>3</sub>Sn applications it is important to understand the effect of neutron irradiation and the presence of APCs on the nanoscale chemical segregation in Nb<sub>3</sub>Sn wires in order to design Nb<sub>3</sub>Sn with better superconducting properties. This work has shown that APT is a useful technique to analyse the nanostructure of Nb<sub>3</sub>Sn wires.</p> |
| first_indexed | 2024-09-25T04:21:00Z |
| format | Thesis |
| id | oxford-uuid:bbdb8e9e-852e-43b4-9783-51e943c5a48f |
| institution | University of Oxford |
| language | English |
| last_indexed | 2024-09-25T04:21:00Z |
| publishDate | 2023 |
| record_format | dspace |
| spelling | oxford-uuid:bbdb8e9e-852e-43b4-9783-51e943c5a48f2024-08-02T15:40:38ZAtom probe tomography analysis of Nb3Sn superconducting wires for fusion reactor and particle accelerator applicationsThesishttp://purl.org/coar/resource_type/c_db06uuid:bbdb8e9e-852e-43b4-9783-51e943c5a48fSuperconductorsMaterialsNuclear fusionAtom-probe field ion microscopyEnglishHyrax Deposit2023Wheatley, LGrovenor, CMoody, M<p>First discovered in 1954, Nb<sub>3</sub>Sn is a low temperature superconductor, which has had a resurgence in interest in recent years. Multiple projects, such as the Hi-Lumi upgrade to the Large Hadron Collider and the fusion reactor ITER have used Nb<sub>3</sub>Sn superconducting magnets, and there are plans to use improved Nb<sub>3</sub>Sn wires for a Future Circular Collider (FCC). Nb<sub>3</sub>Sn is the second most commercially available superconductor after NbTi, which revolutionised the medical sector making MRI machines possible. However, NbTi has a maximum field of 14 T, compared to the higher maximum field of 28 T for Nb<sub>3</sub>Sn.</p> <br> <p>The FCC target is 1500 Amm<sup>-2</sup> at 16 T, much more challenging than previous applications of Nb<sub>3</sub>Sn. To reach this target fluxons, which are 3 - 4 nm in radius in Nb<sub>3</sub>Sn, need to be trapped at defects within the Nb<sub>3</sub>Sn microstructure. Historically, grain refinement has been the main method of increasing the J<sub>c</sub> by maximising the grain boundary area which can pin fluxons. Commercial Nb<sub>3</sub>Sn wires have a grain size of ≈ 100 nm, however, it is difficult to reduce the grain size further and still produce a homogeneous Nb<sub>3</sub>Sn layer with favourable superconducting properties. To increase J<sub>c</sub> to reach the FCC target, artificial pinning centres (APCs), on the scale of the fluxons are required.</p> <br> <P>Considering the importance of the nanoscale structure on the superconducting properties of Nb<sub>3</sub>Sn, little is known about nanoscale chemical segregation within Nb<sub>3</sub>Sn. In this work, Atom Probe Tomography (APT) has been used to understand the nanoscale structure of two different types of Nb<sub>3</sub>Sn wires, restacked-rod-processed (RRP®) and rod-in-tube (RIT) type wires. The first set of results focuses on a commercial RRP® wire doped with Ti and a comparative RRP® wire, irradiated at a neutron fluence of 2.82 x 10<sup>22</sup>m<sup>-2</sup> in the TRIGA II reactor. The inter-grain compositions, intra-grain compositions and any additional features such as dislocations were studied. Both RRP® samples had intra-grain compositions which were formed of two different, non-equilibrium compositions, one higher in Nb and one lower in Nb. The irradiated RRP® sample had a lower volume of high Nb compared to the as-received sample, this suggests that irradiation induced diffusion has occurred due to the excess of vacancies produced during neutron irradiation.</p> <br> <p>The second set of results focuses on a RIT test wire which reached the high J<sub>c</sub> requirement for the FCC. The pinning curve from this wire suggested the presence of APCs, despite no intentional source of oxygen added to the wire, to produce APCs through internal oxidation. An Electron probe micro-analyser (EPMA) and APT have been used to determine the oxygen concentration in the unreacted and reacted Nb-4Ta-1Hf (at%) alloy, with evidence of HfO<sub>2</sub> nanoparticles in the reacted Nb-4Ta-1Hf alloy. In a similar way to the RRP® samples, the intra-grain and inter-grain compositions of the Nb<sub>3</sub>Sn layer have been measured, and the size and number density of HfO<sub>2</sub> APCs have been calculated. Additional features have been analysed, such as a residual Nb<sub>6</sub>Sn<sub>5</sub> layer at the edge of the Nb<sub>3</sub>Sn region and residual Cu rich phases trapped within the Nb<sub>3</sub>Sn layer. Evidence of HfO<sub>2</sub> in the reacted Nb-4Ta-1Hf alloy and the Nb<sub>6</sub>Sn<sub>5</sub> layer shows HfO<sub>2</sub> nanoparticles were formed prior to Nb<sub>3</sub>Sn and that the HfO<sub>2</sub> nanoparticles may have acted as Zener pinning sites to reduce the grain size of the Nb<sub>3</sub>Sn. Nb<sub>6</sub>Sn<sub>5</sub> has been shown to have a higher Cu solubility than Nb<sub>3</sub>Sn, perhaps explaining the trapped regions of Cu rich phases within the Nb<sub>3</sub>Sn.</p> <br> <p>For future Nb<sub>3</sub>Sn applications it is important to understand the effect of neutron irradiation and the presence of APCs on the nanoscale chemical segregation in Nb<sub>3</sub>Sn wires in order to design Nb<sub>3</sub>Sn with better superconducting properties. This work has shown that APT is a useful technique to analyse the nanostructure of Nb<sub>3</sub>Sn wires.</p> |
| spellingShingle | Superconductors Materials Nuclear fusion Atom-probe field ion microscopy Wheatley, L Atom probe tomography analysis of Nb3Sn superconducting wires for fusion reactor and particle accelerator applications |
| title | Atom probe tomography analysis of Nb3Sn superconducting wires for fusion reactor and particle accelerator applications |
| title_full | Atom probe tomography analysis of Nb3Sn superconducting wires for fusion reactor and particle accelerator applications |
| title_fullStr | Atom probe tomography analysis of Nb3Sn superconducting wires for fusion reactor and particle accelerator applications |
| title_full_unstemmed | Atom probe tomography analysis of Nb3Sn superconducting wires for fusion reactor and particle accelerator applications |
| title_short | Atom probe tomography analysis of Nb3Sn superconducting wires for fusion reactor and particle accelerator applications |
| title_sort | atom probe tomography analysis of nb3sn superconducting wires for fusion reactor and particle accelerator applications |
| topic | Superconductors Materials Nuclear fusion Atom-probe field ion microscopy |
| work_keys_str_mv | AT wheatleyl atomprobetomographyanalysisofnb3snsuperconductingwiresforfusionreactorandparticleacceleratorapplications |