Fabrication of Graded Germanium-doped CH Shells

One of the capsule designs for achieving ignition on the National Ignition Facility (NIF) is a 2~mm diameter graded germanium-doped plastic (CH) shell with a 160~$\mu$m thick wall. The graded Ge-doped design allows a somewhat relaxed outer surface finish requirement than the original uniformly Ge-doped CH design. We produced Ge-doped shells that met nearly all the NIF design specifications using plasma-assisted polymer deposition with (CH$_3$)$_4$Ge as the doping source. The Ge concentration, layer thickness and surface smoothness were determined by quantitative contact radiography, x-ray fluorescence analysis, and atomic force microscopy. The shell has an inner 10~$\mu$m undoped CH layer, followed by 481~$\mu$m of 0.83~atom \% Ge-doped CH, 10~$\mu$m of 0.38~atom \% Ge-doped CH and then 90~$\mu$m of undoped CH, with an outer surface rms roughness of $\sim$24~nm (modes 10-1000). A few isolated surface domes about 1~$\mu$m high and 20~$\mu$m in diameter were present.