What is magnetic self-organization?

Self-organization here refers to the following process. A system is driven such that excess free energy excites instabilities (and possibly turbulence) that cause the system to relax to a lower energy state by rearranging (self-organizing) its large-scale structure. In magnetic self-organization the instabilities are magnetic (the magnetic field fluctuates in space or time); and large-scale quantities that are rearranged include the magnetic field, and possibly other quantities such as flow and pressure. Laboratory plasmas may be driven to a state of high magnetic energy by an applied electric field. Magnetospheric substorms may be driven by the solar wind; solar dynamo and coronal activity may be driven by convection and rotation; magnetic activity in accretion disks may be driven by rotation. The specifications of the drive differ between situations; and in some of the phenomena rearrangement of quantities other than the magnetic field may dominate. But, the phenomena strongly share underlying physics.

What are the major physics questions?

The topics, and sample questions the center will address are as follows (links to research plans are provided):

(1) Dynamo effects: What determines the spontaneous generation of magnetic fields throughout the universe? The existence of a dynamo is not in doubt ­ it has been demonstrated in laboratory plasmas, and observed in stars and planets. Our focus is the underlying physics. Magnetohydrodynamic (MHD) theory predicts the initial, exponential growth of a seed magnetic field. There are two major questions we seek to answer: What determines the nonlinear saturation of the dynamo? Are there new dynamo mechanisms beyond that of the standard MHD models? Both questions, and most of those that follow, require the high electrical conductivity (high Lundquist number) uniquely provided by a high temperature plasma.

(2) Magnetic reconnection: What determines the spatial scales and rates of reconnection in coronae of stars, in stellar accretion disks, and during relaxation of laboratory plasmas? How do the local features of reconnection influence the global structure?

(3) Magnetic helicity conservation and transport: Is magnetic helicity, a topological measure of magnetic field knottedness, a conserved quantity during self-organization, and is it a key constraint for dynamos, and for magnetic relaxation in the solar corona and the laboratory?

(4) Angular momentum transport: What determines momentum transport essential for the disk accretion of matter onto compact objects such as black holes and for the sudden rotation changes in laboratory plasmas? Is the magnetic Reynolds stress, the leading theory for both laboratory and astrophysics, correct?

(5) Ion heating: Why are ions in the solar wind, laboratory plasmas, and possibly accretion disks, hotter than the electrons? How do relativistic ions in galactic cosmic rays acquire their energy?

(6) Magnetic chaos and transport: How are plasma energy and particles transported along magnetic field lines that wander chaotically, as occurs for cosmic rays in the heliosphere and galaxy, laboratory plasmas, and thermally inhomogeneous interstellar and intergalactic plasmas? What do we plan to do? Through a series of meetings held over the first several months of the Center life, we have assembled work plans in each of the six topics, as follows.