Issues of Liner-Plasma Compression

For several decades, the notion of compression of plasma to fusion conditions by liner implosion has been pursued by several groups. This quest has often achieved success with some form of liner implosion technology, but not in the actual compression of plasma. Several plasma targets have been proposed, ranging from plasma magnetized to reduce heat transfer, but mechanically-supported by the liner, to plasmas confined and supported by magnetic field, in some configuration of open and closed field-lines. In all cases, the principal issue remains one of preventing the high atomic-number material of the liner from penetrating the plasma and countering the gain in plasma temperature sought by compression. Two factors foster development of such deleterious penetration: the creation of a liquid/vapor layer at the liner surface at high magnetic fields, and disruption of this layer by Rayleigh-Taylor instability in the final stages of plasma compression. The latter factor, of course, depends on the desired efficiency of energy transfer from liner kinetic energy to the plasma. In reactor concepts, the efficiency needs to be high in order to reduce the total system energy and size to attractive values. Within a general review of issues of liner compression of plasma, we discuss reactor cost optimization by use of plasma at pressures intermediate between the values of conventional magnetically- or inertially-confined fusion concepts. We also describe the development of an equilibrium layer of vapor adjacent to the liner surface at high magnetic fields, and the consequences of liner deceleration and rebound for reactor concepts and research progress.