Number 288 (Story #2), September 26, 1996 by Phillip F. Schewe and Ben Stein PROBING ARTIFICIAL PLASMAS 6 TIMES DENSER THAN AT THE CENTER OF THE SUN is the goal of scientists working on the proposed National Ignition Facility (NIF), a U.S. research center where scientists plan to study nuclear fusion and other processes involving extremely dense plasmas. Expected to be funded and completed by the early part of next decade, NIF will use high-power lasers to achieve, among other things, inertial confinement fusion, in which a deuterium-tritium (D-T) fuel pellet is compressed to extremely high densities. In experiments that aim to achieve self- sustaining fusion reactions, the densities are expected to reach up to 1000 grams per cubic centimeter (compared to the 150-160 g/cc at the center of the Sun and the 40-50 g/cc reported for D-T plasmas at existing facilities such as OMEGA in Rochester and ILE in Japan.) NIF would therefore create the densest conventional plasmas ever to exist on Earth. To determine what goes on at the center of such hard-to-penetrate plasmas, researchers at MIT, Livermore, and University of Rochester have proposed studying "tertiary protons," which are created at the end of a three-step process starting with the fusion of deuterium and tritium nuclei. These tertiary protons would be energetic enough (~30 MeV) to escape the dense plasma and reach a network of detectors. Energy losses of protons emerging from all different directions can show whether the fuel pellet compresses uniformly (important for maximizing the efficiency of fusion reactions) and also yield information on the density and size of the region in which fusion occurs. In the near future, the researchers plan to study tertiary protons created in D-T reactions at OMEGA. (R. D. Petrasso et al., Physical Review Letters, 23 September 1996)