Diffusion wall time in toroidally segmented shell aka Armadillo
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arXiv
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| Formato: | Preprint |
| Publicado: |
2026
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| _version_ | 1866915983337193472 |
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| author | Abate, D. Corbioli, A. |
| author_facet | Abate, D. Corbioli, A. |
| contents | An analytical expression for the diffusion wall time of a toroidally segmented conducting shell (the Armadillo configuration) is derived by extending the continuous-shell formulation to include the non-axisymmetric current pattern imposed by the presence of toroidal gaps. The segmentation constrains the toroidal current to follow a standing-wave structure that vanishes at the gap locations, introducing a correction to the effective resistivity that grows quadratically with the number of gaps and competes with the intrinsic toroidal scale of the mode. As a result, the wall time decreases rapidly for low toroidal-number modes, more gradually for intermediate ones, and only for sufficiently large segmentation in the high-n regime. The analytical formula shows agreement within 10% against 3D electromagnetic numerical calculations. The resulting expression provides a compact tool for estimating the wall time of segmented conducting structures surrounding the plasma, with direct applications to MHD stability and control in both RFPs and tokamaks. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2605_02018 |
| institution | arXiv |
| publishDate | 2026 |
| record_format | arxiv |
| spellingShingle | Diffusion wall time in toroidally segmented shell aka Armadillo Abate, D. Corbioli, A. Plasma Physics An analytical expression for the diffusion wall time of a toroidally segmented conducting shell (the Armadillo configuration) is derived by extending the continuous-shell formulation to include the non-axisymmetric current pattern imposed by the presence of toroidal gaps. The segmentation constrains the toroidal current to follow a standing-wave structure that vanishes at the gap locations, introducing a correction to the effective resistivity that grows quadratically with the number of gaps and competes with the intrinsic toroidal scale of the mode. As a result, the wall time decreases rapidly for low toroidal-number modes, more gradually for intermediate ones, and only for sufficiently large segmentation in the high-n regime. The analytical formula shows agreement within 10% against 3D electromagnetic numerical calculations. The resulting expression provides a compact tool for estimating the wall time of segmented conducting structures surrounding the plasma, with direct applications to MHD stability and control in both RFPs and tokamaks. |
| title | Diffusion wall time in toroidally segmented shell aka Armadillo |
| topic | Plasma Physics |
| url | https://arxiv.org/abs/2605.02018 |