Several choices exist in the design and production
of capsules intended to ignite and propagate fusion burn
of the deuterium–tritium (D–T) fuel when imploded
by indirect drive at the National Ignition Facility (NIF).
These choices include ablator material, ablator dopant
concentration and distribution, capsule dimensions, and
X-ray drive profile (shock timings and strengths). The
choice of ablator material must also include fabrication
and material characteristics, such as attainable surface
finishes, permeability, strength, transparency to radio
frequency and infrared radiation, thermal conductivity,
and material homogeneity. Understanding the advantages
and/or limitations of these choices is an ongoing effort
for LLNL and LANL designers. At this time, simulations
in one-, two-, and three-dimensions show that capsules
with either a copper-doped beryllium or a polyimide (C22H10N2O4)
ablator material have both the least sensitivity to initial
surface roughnesses and favorable fabrication qualities.
Simulations also indicate the existence of capsule designs
based on these ablator materials which ignite and burn
when imploded by less than nominal laser performance (900-kJ
energy, 250-TW power, producing 250-eV peak radiation temperature).
We will describe and compare these reduced-scale capsules,
in addition to several designs which use the expected 300-eV
peak X-ray drive obtained from operating the NIF laser
at 1.3 MJ and 500 TW.
Automated analysis of hot spot X-ray images at the National Ignition
Facility
