Without plasma flow (left); with plasma flow (right).

Plasma science (the study of ionized gases) is critical to the development of fusion energy (involving the fusion of nuclei), which could be an abundant energy source in the future. Efficient confinement of hot plasma, which is necessary to create fusion energy, is prevented by small-scale instabilities that cause turbulence. Office of Science support has played a major role in efforts to understand and reduce plasma turbulence. U.S. researchers have demonstrated that flow shear (radially varying plasma flow velocities) can suppress the turbulence responsible for transporting particles and energy across the magnetic field in fusion devices. Experimental, theoretical, and computer simulation studies have shown that flow shear produces localized, sharply defined transport barriers that alter the physics of energy and particle transport. The first improved plasma confinement mode resulting from the onset of a sharply defined transport barrier was discovered by German researchers in the early 1980s. More recently, U.S. researchers identified flow shear as the mechanism that produces this edge transport barrier. Sheared flows also have been shown to play a dominant role in the formation of other plasma confinement modes.

Scientific Impact: The enhanced confinement regimes resulting from flow shear stabilization of turbulence are of considerable scientific interest; systems seldom self-organize to a higher energy state, with reduced turbulence and transport, when an additional source of free energy is applied.

Social Impact: These advances will help promote the availability of fusion as an inexhaustible, safe, and environmentally attractive energy source. In addition to the general public, beneficiaries may include industries that use plasma science and technology, including makers of semiconductors and space propulsion systems.

Reference: Z. Lin, et al., Science, 281, 1835 (1998)

"Comparisons and Physics Basis of Tokamak Transport Models and Turbulence Simulations," A. M. Dimits, G. Bateman, M. A. Beer, B. I. Cohen, ..., Phys. Plasmas 7, 969 (2000)

URL: http://fusion.gat.com/theory/pmp/

Technical Contact: Steve Eckstrand, Research Division, 301-903-5546

Press Contact: Jeff Sherwood, DOE Office of Public Affairs, 202-586-5806

SC-Funding Office: Office of Fusion Energy Sciences