Capsule design for the National Ignition Facility

Several choices exist in the design and production of capsules intended to ignite and propagate fusion burn of the DT fuel when imploded by indirect drive at the National Ignition Facility. 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 the nominal NIF laser (1.3 MJ, 500 TW)