Magnetic helicity in the solar corona
Thesis/Dissertation
·
OSTI ID:5472244
The relation of magnetic helicity to the structure and evolution of magnetic fields is discussed. Helicity measures the topological complexity of field lines: if a configuration is divided into a collection of flux tubes, then helicity arises from the linkage and knotting of the tubes as well as from internal field line structure such as twist and kinking. If helicity is integrated over a volume not bounded by a magnetic surface (for example, the solar atmosphere), then the helicity integral cannot be related to field-line linkage structure and will not be gauge-invariant. However, a well-defined relative measure of helicity for arbitrary volumes is shown to exist. The potential field, which is uniquely determined by boundary conditions, provides a universal reference field for this relative helicity measure. The time derivative of the relative helicity of a volume measures helicity flow across the boundaries of the volume, as well as internal dissipation. Helicity flow from the interior of the sun into the corona can be determined by observing the motion of photospheric magnetic flux. Rigorous limits have been placed on magnetic helicity dissipatior in a resistive plasma. These limits strongly suggest that helicity nonconservation in the corona is negligible.
- Research Organization:
- Harvard Univ., Boston, MA (USA)
- OSTI ID:
- 5472244
- Country of Publication:
- United States
- Language:
- English
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