Coronal fluid-dynamics in laser fusion

The fluid-dynamics of the corona ejected by laser-fusion targets in the direct-drive approach (thermal radiation and atomic physics unimportant) is discussed. A two-fluid model involves inverse bremsstrahlung absorption, refraction, different ion and electron temperatures with energy exchange, different ion and electron velocities and magnetic field generation, and their effect on ion-electron friction and heat flux. Four dimensionless parameters determine coronal regimes for one-dimensional flows under uniform irradiation. One additional parameter is involved in two-dimension al prob­ lems, including the stability of one-dimension al flows, and the smoothing of non­ uniform driving. We discuss here the fluid dynamics of the corona of fully ionized plasma ejected by a laser-irradiated target. The motivation of such a discussion is that, first, coronal flow is a special field in fluid dynamics, and, second, the variety of existing flow regimes needs to be explored prior to a full understanding of laser fusion, particularly of the compression of the imploding (part of the) target. We restrict our study to the direct-drive approach, for which thermal radiation and atomic physics play no dominant role. The special features of the corona are elaborated in Sec. 2. The equations involved in its analysis and the dimensionless parameters characterizing the coronal regimes are considered in Sees. 3 and 4 respectively. In the following section we review the limiting regimes and time behaviours for uniform laser irradiation, leading to one-dimension al problems described by systems of ordinary differential equations; their solutions involve non-linear eigenvalue determination and provide basic universal laws. In Sec. 6 we consider weakly two-dimensional problems that include the stability of 1-D flows, and the coronal smoothing of weakly non-uniform irradiation of targets. Some effects not included in the model of Sec. 3 are discussed in Sec. 7.