Sputter-deposited Be ablators for NIF target capsules

We have performed a series of preliminary experiments to determine whether sputter deposition of doped Be is a practical route to producing NIF target capsules with Be ablators. Films ranging in thickness from 7 to similar to 120 mu m have been deposited on spherical polymer mandrels using a bounce pan to ensure uniform coating. With no voltage bias applied to the pan, relatively porous coatings were formed that were highly permeable to hydrogen. The surface finish of these films ranged from similar to 250 nm rms for 13-mu m-thick films to a minimum of similar to 75 nm rms for an 80-mu m-thick film. Application of a voltage bias was found to significantly modify the film morphology. At a bias of 120 V, 7-mu m-thick films with a dense, fine-grained microstructure were produced. These capsules had a reflective surface with a 50 nm rms roughness. Finally, to demonstrate the ability to produce a graded dopant profile, a coating was produced in which the concentration of added Cu was varied from 2.5 atom % at the beginning to zero after 40 mu m of deposition.