In both laboratory toroidal plasmas and astrophysical disks are observed to rotate in the toroidal direction. It is also known that the toroidal angular momentum is transported in the radial direction in both cases. In the MST experiment, during a reconnection event the rotation of the plasma is abruptly changed (as shown in the figure). In the astrophysical situation, the force that moves the momentum outward radially is believed to arise from flow-driven instabilities. Theoretical work applied to the laboratory situtation has established that the forces can arise from current-driven instabilities that cause reconnection. The space and time varying fluctuations associated with the reconnection, produce a large-scale forces (Lorentz forces and fluid Reynolds stress) that alter the rotation. Future work will focus on comparison with experiment and consideration of whether this mechanism is active is astrophysical plasmas.

Rotation of the toroidal lab plasma showing sudden changes during reconnection (or relaxation) events in the MST experiment at Wisconsin.

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