Electric field effects during disruptions
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...
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Veröffentlicht in: | Physics of plasmas 2024-10, Vol.31 (10) |
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Format: | Artikel |
Sprache: | eng |
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Zusammenfassung: | 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
∼Te/eB and the long correlation distances
aT produce a large scale flow
∼Te/eBaT. This cross-field diffusion and flow are important for sweeping impurities into the core of a disrupting tokamak. The analysis separates the electric field in a plasma into the sum of a divergence-free,
E→B, and a curl-free,
E→q, part, a Helmholtz decomposition. The divergence-free part of
E→ determines the evolution of the magnetic field. The curl-free part enforces quasi-neutrality,
E→q=−∇→Φq. Magnetic helicity evolution gives the required boundary condition for a unique Helmholtz decomposition and an unfortunate constraint on steady-state tokamak maintenance. |
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ISSN: | 1070-664X 1089-7674 |
DOI: | 10.1063/5.0219727 |