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| Format: | Preprint |
| Published: |
2026
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| Online Access: | https://arxiv.org/abs/2604.08321 |
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| _version_ | 1866909034024534016 |
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| author | Bhattacharjee, Amitava |
| author_facet | Bhattacharjee, Amitava |
| contents | Ion temperature clamping -- the saturation of the ion temperature regardless of heating power -- is observed across stellarator experiments. We propose a minimal model based on Anderson localisation. Starting from a reduced fluid model for drift waves [Phys. Fluids 26, 880 (1983)], we show that aperiodic stellarator geometry leads to a quasiperiodic Hill equation for the ion-temperature-gradient (ITG) mode structure. In a tight-binding approximation this equation reduces to an Aubry--Andre--Harper difference equation, suggesting an Anderson-localisation mechanism for ITG eigenfunctions. We identify a three-threshold ordering: the linear instability threshold lies below the Anderson localisation threshold, which lies below the observed clamp. This is conjectured to create a low-transport second regime above the instability threshold, qualitatively analogous to the second stability regime of MHD ballooning theory, and provides a power-independent lower bound on the observed gradient. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2604_08321 |
| institution | arXiv |
| publishDate | 2026 |
| record_format | arxiv |
| spellingShingle | Anderson Localization of Ion-Temperature-Gradient Modes and Ion Temperature Clamping in Aperiodic Stellarators Bhattacharjee, Amitava Plasma Physics Ion temperature clamping -- the saturation of the ion temperature regardless of heating power -- is observed across stellarator experiments. We propose a minimal model based on Anderson localisation. Starting from a reduced fluid model for drift waves [Phys. Fluids 26, 880 (1983)], we show that aperiodic stellarator geometry leads to a quasiperiodic Hill equation for the ion-temperature-gradient (ITG) mode structure. In a tight-binding approximation this equation reduces to an Aubry--Andre--Harper difference equation, suggesting an Anderson-localisation mechanism for ITG eigenfunctions. We identify a three-threshold ordering: the linear instability threshold lies below the Anderson localisation threshold, which lies below the observed clamp. This is conjectured to create a low-transport second regime above the instability threshold, qualitatively analogous to the second stability regime of MHD ballooning theory, and provides a power-independent lower bound on the observed gradient. |
| title | Anderson Localization of Ion-Temperature-Gradient Modes and Ion Temperature Clamping in Aperiodic Stellarators |
| topic | Plasma Physics |
| url | https://arxiv.org/abs/2604.08321 |