Electric field effects during disruptions
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arXiv
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| Format: | Preprint |
| Publié: |
2024
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| _version_ | 1866910587885191168 |
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| author | Boozer, Allen H |
| author_facet | Boozer, Allen H |
| contents | Tokamak disruptions are associated with breaking magnetic surfaces, which makes magnetic field lines chaotic in large regions of the plasma. The enforcement of quasi-neutrality in a region of chaotic field lines requires an electric potential that has both short and long correlation distances across the magnetic field lines. The short correlation distances produce a Bohm-like diffusion coefficient $\sim T_e/eB$ and the long correlation distances $a_T$ produce a large scale flow $\sim T_e/eB a_T$. This cross-field diffusion and flow are important for sweeping impurities into the core of a disrupting tokamak. The analysis separates of the electric field in a plasma into the sum of a divergence-free, $\vec{E}_B$, and a curl-free, $\vec{E}_q$, part, a Helmholtz decomposition. The divergence-free part of $\vec{E}$ determines the evolution of the magnetic field. The curl-free part enforces quasi-neutrality, $\vec{E}_q=-\vec{\nabla}Φ_q$. Magnetic helicity evolution gives the required boundary condition for a unique Helmholtz decomposition and an unfortunate constraint on steady-state tokamak maintenance. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2404_09744 |
| institution | arXiv |
| publishDate | 2024 |
| record_format | arxiv |
| spellingShingle | Electric field effects during disruptions Boozer, Allen H Plasma Physics Tokamak disruptions are associated with breaking magnetic surfaces, which makes magnetic field lines chaotic in large regions of the plasma. The enforcement of quasi-neutrality in a region of chaotic field lines requires an electric potential that has both short and long correlation distances across the magnetic field lines. The short correlation distances produce a Bohm-like diffusion coefficient $\sim T_e/eB$ and the long correlation distances $a_T$ produce a large scale flow $\sim T_e/eB a_T$. This cross-field diffusion and flow are important for sweeping impurities into the core of a disrupting tokamak. The analysis separates of the electric field in a plasma into the sum of a divergence-free, $\vec{E}_B$, and a curl-free, $\vec{E}_q$, part, a Helmholtz decomposition. The divergence-free part of $\vec{E}$ determines the evolution of the magnetic field. The curl-free part enforces quasi-neutrality, $\vec{E}_q=-\vec{\nabla}Φ_q$. Magnetic helicity evolution gives the required boundary condition for a unique Helmholtz decomposition and an unfortunate constraint on steady-state tokamak maintenance. |
| title | Electric field effects during disruptions |
| topic | Plasma Physics |
| url | https://arxiv.org/abs/2404.09744 |