This paper reviews the current direct-drive ignition capsule designed for t
he National Ignition Facility (NIF) [M. D. Campbell and W. J. Hogan, Plasma
Phys. Control. Fusion 41, B39 (1999)]. The ignition design consists of a c
ryogenic deuterium-tritium (DT) shell contained within a very thin CH shell
. To maintain shell integrity during the implosion, the target is placed on
an isentrope approximately three times that of Fermi-degenerate DT (alpha
=3). One-dimensional studies show that the ignition design is robust. Two-d
imensional simulations examine the effects on target performance due to las
er imprint, power imbalance, and inner- and outer-target-surface roughness.
Results from these studies indicate that the capsule gain can be scaled to
the ice/vapor surface deformation at the end of the acceleration stage of
the implosion. The physical reason for gain reduction as a function of incr
easing nonuniformities is examined. Simulations show that direct-drive targ
et gains in excess of 30 can be achieved for an inner-ice-surface roughness
of 1 mum rms, an on-target power imbalance of 2% rms, and by using the bea
m-smoothing technique SSD with 1 THz and two color cycles. (C) 2001 America
n Institute of Physics.