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 deuterium-tritium (D-T) fuel when i mploded by indirect drive at the National Ignition Facility (NIF). These ch oices include ablator material, ablator dopant concentration and distributi on, capsule dimensions, and X-ray drive profile (shock timings and strength s). The choice of ablator material must also include fabrication and materi al characteristics, such as attainable surface finishes, permeability, stre ngth, transparency to radio frequency and infrared radiation, thermal condu ctivity, and material homogeneity. Understanding the advantages and/or limi tations of these choices is an ongoing effort for LLNL and LANL designers. At this time, simulations in one-, two-, and three-dimensions show that cap sules with either a copper-doped beryllium or a polyimide (C22H10N2O4) abla tor material have both the least sensitivity to initial surface roughnesses and favorable fabrication qualities. Simulations also indicate the existen ce of capsule designs based on these ablator materials which ignite and bur n when imploded by less than nominal laser performance (900-kJ energy, 250- TW power, producing 250-eV peak radiation temperature). We will describe an d compare these reduced-scale capsules, in addition to several designs whic h use the expected 300-eV peak X-ray drive obtained from operating the NIF laser at 1.3 MJ and 500 TW.