Lawrence Livermore National Laboratory
Plasma Physics
Almost all of the observable matter in the universe is in the plasma state. Formed at high temperatures when electrons are stripped from neutral atoms, plasmas consist of freely moving ions and free electrons. They are often called the "fourth state of matter" because their unique physical properties distinguish them from solids, liquids and gases.
Characteristics of typical plasmas
Plasma densities and temperatures vary widely, from the cold gases of interstellar space to the extraordinarily hot, dense cores of stars and inside a nuclear weapon. On one end of the spectrum, plasma physicists study conditions of high vacuum, with only a few particles in a volume of one cubic centimeter – about the volume of a sugar cube. On the other end of the density range, plasmas with densities sometimes well above 1,000 times the density of a solid occur in stellar interiors and in laboratory experiments that attempt to reproduce the processes in the sun. Although we now most commonly encounter plasmas in energy-efficient light bulbs, plasmas may hold their greatest potential as a future inexhaustible source of energy (see Inertial Fusion Energy).
Two areas of plasma physics have been addressed with experiments using high-energy lasers and both are very relevant to the attempt to create inertial fusion (see How to Make a Star). First are studies of the phenomena created by the laser interacting with the plasma. Of particular importance in this area are two mechanisms of laser-plasma coupling: "stimulated Brillouin scattering" and "stimulated Raman scattering," two ways the energy of the laser beam is shared with the plasma (see Laser-Plasma Interactions). Both effects need to be minimized in order to drive the implosion of the ignition capsule as efficiently as possible.
The second area involves attempts to use the laser to emulate other phenomena occurring in nature. This research is also important to inertial fusion, but it extends well beyond that into fundamental areas of science, such as interpenetrating plasmas and plasma flow in a magnetic field.
The capabilities of NIF will allow production of hot dense plasmas that are sufficiently large and homogeneous to allow their detailed characterization, and thus to study these phenomena. NIF will allow measurement of electron and ion temperatures, charge states, electron density and plasma flow velocities, all of which are essential for understanding experiments on the two basic areas of plasma physics described above.
More Information
Basic Research Directions for User Science at the National Ignition Facility, National Nuclear Security Administration and U.S. Department of Energy Office of Science, November 2011
"Taking on the Stars: Teller´s Contributions to Plasma and Space Physics," Science & Technology Review, July/August 2007
"Duplicating the Plasmas of Distant Stars," Science & Technology Review, April 1999
