Role of microstructure on flux expulsion of superconducting radio frequency cavities
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arXiv
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| Main Authors: | , , , , , , , , , , |
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| Format: | Preprint |
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2024
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| _version_ | 1866909334305243136 |
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| author | Khanal, B. D. Balachandran, S. Chetri, S. Barron, M. Mullinix, R. Williams, A. Xu, P. Ingrole, A. Lee, P. J. Ciovati, G. Dhakal, P. |
| author_facet | Khanal, B. D. Balachandran, S. Chetri, S. Barron, M. Mullinix, R. Williams, A. Xu, P. Ingrole, A. Lee, P. J. Ciovati, G. Dhakal, P. |
| contents | The trapped residual magnetic flux during the cool-down due to the incomplete Meissner state is a significant source of radio frequency losses in superconducting radio frequency (SRF) cavities. Here, we show a clear correlation between the niobium microstructure in elliptical cavity geometry and flux expulsion behavior. In particular, a traditionally fabricated Nb cavity half cell from an annealed poly-crystalline Nb sheet after an 800 $^\circ$C heat treatment leads to a bi-modal microstructure that ties in with flux trapping and inefficient flux expulsion. This non-uniform microstructure is related to varying strain profiles along the cavity shape. A novel approach to prevent this non uniform microstructure is presented by fabricating a 1.3 GHz single cell Nb cavity with a cold-worked sheet and subsequent heat treatment leading to better flux expulsion after 800 $^\circ$C/3 h. Microstructural evolution by electron backscattered diffraction-orientation imaging microscopy on cavity cutouts, and flux pinning behavior by dc-magnetization on coupon samples confirms a reduction in flux pinning centers with increased heat treatment temperature. The heat treatment temperature dependent mechanical properties and thermal conductivity are reported. The significant impact of cold-work in this study demonstrates clear evidence for the importance of microstructure required for high-performance superconducting cavities with reduced losses caused by magnetic flux trapping. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2410_02397 |
| institution | arXiv |
| publishDate | 2024 |
| record_format | arxiv |
| spellingShingle | Role of microstructure on flux expulsion of superconducting radio frequency cavities Khanal, B. D. Balachandran, S. Chetri, S. Barron, M. Mullinix, R. Williams, A. Xu, P. Ingrole, A. Lee, P. J. Ciovati, G. Dhakal, P. Accelerator Physics Superconductivity The trapped residual magnetic flux during the cool-down due to the incomplete Meissner state is a significant source of radio frequency losses in superconducting radio frequency (SRF) cavities. Here, we show a clear correlation between the niobium microstructure in elliptical cavity geometry and flux expulsion behavior. In particular, a traditionally fabricated Nb cavity half cell from an annealed poly-crystalline Nb sheet after an 800 $^\circ$C heat treatment leads to a bi-modal microstructure that ties in with flux trapping and inefficient flux expulsion. This non-uniform microstructure is related to varying strain profiles along the cavity shape. A novel approach to prevent this non uniform microstructure is presented by fabricating a 1.3 GHz single cell Nb cavity with a cold-worked sheet and subsequent heat treatment leading to better flux expulsion after 800 $^\circ$C/3 h. Microstructural evolution by electron backscattered diffraction-orientation imaging microscopy on cavity cutouts, and flux pinning behavior by dc-magnetization on coupon samples confirms a reduction in flux pinning centers with increased heat treatment temperature. The heat treatment temperature dependent mechanical properties and thermal conductivity are reported. The significant impact of cold-work in this study demonstrates clear evidence for the importance of microstructure required for high-performance superconducting cavities with reduced losses caused by magnetic flux trapping. |
| title | Role of microstructure on flux expulsion of superconducting radio frequency cavities |
| topic | Accelerator Physics Superconductivity |
| url | https://arxiv.org/abs/2410.02397 |