Physics Colloquium - Can Magnetically Confined Plasmas Help Explain Solar Physics and Space Weather

Dr. Linda Sugiyama

 Massachusetts Institute of Technology

The surface of the sun transmits the enormous energy generated by fusion in the solar interior into space. A significant fraction of the energy and particles that reach the earth are ejected by impulsive local events, such as solar flares and coronal mass ejections, that are associated with the growth of magnetic loops, or flux ropes, into the solar corona. The difficulty of remotely measuring magnetic fields and currents means that the flux rope structure, and thus the trigger conditions and evolution of these events, are partly conjectural and usually discussed using simplified plasma models.

On the other hand, magnetically confined toroidal plasmas have been extensively investigated in the laboratory and their steady states are well understood. Despite quite different parameters, the basic relations still apply.

Toroidal plasmas are intrinsically unstable to outward radial expansion, due the force imbalance between the small and large radius sides of the torus. For coronal loops, a consistent MHD solution shows that the non-axisymmetric solar gravity and loop internal plasma pressure, previously ignored as small, can balance the expansion force.

Three possible steady states are found, that appear to describe a range of important types of coronal flux ropes, where the loop height scales with the MHD gravity parameter.

The solutions also have much broader applications.