Preparation of NIF Scale Poly ((alpha)-METHYLSTYRENE) Mandrels

Takagi, M ; Cook, R ; McQuillan, B ; Elsner, F ; Stephens, R ; Nikroo, A ; Paguio, S

Lawrence Livermore National Laboratory

关键词: Glow Discharges;    Solvents;    Agglomeration;    Symmetry;    70 Plasma Physics And Fusion Technology;   

DOI  :  10.2172/15005032
RP-ID  :  UCRL-ID-148920
RP-ID  :  W-7405-ENG-48
RP-ID  :  15005032

美国|英语

来源: UNT Digital Library

【 摘 要 】

All planned National Ignition Facility (NIF) capsule targets except machined beryllium require a plastic mandrel upon which the ablator is applied. This mandrel must at least meet if not exceed the symmetry and surface finish requirements of the final capsule. The mandrels are produced by a two-step process. In the first step a thin-walled poly({alpha}-methylstyrene)(P{alpha}MS) shell is produced using microencapsulation techniques. This shell is overcoated with 10 to 15 {micro}m of glow discharge polymer (GDP) and then pyrolyzed at 300 C. This pyrolysis causes the P{alpha}MS to depolymerize to gas phase monomer that diffuses away through the more thermally stable plasma polymer shell, which retains all the symmetry of the original P{alpha}MS shell. Thus our challenge has been to produce 2-mm-diameter P{alpha}MS shells to serve as these initial ''decomposable'' mandrels that meet or exceed the current NIF design specifications. The basic microencapsulation process used in producing P{alpha}MS mandrels involves using a droplet generator to produce a water droplet (Wl) encapsulated by a fluorobenzene solution of P{alpha}MS (O), this compound droplet being suspended in a stirred aqueous bath (W2). Historically this bath has contained poly(vinyl alcohol) (PVA, 88% hydrolyzed, mol. wt. {approx}25,000 g/mol) to prevent agglomeration of the initially fluid compound droplets. As the compound droplets are stirred in the bath, the fluorobenzene solvent slowly dissipates leaving a solid P{alpha}MS shell. The internal water is subsequently removed by low temperature drying. We found using these techniques that 2-mm shells could easily be produced, however their low mode sphericity did not meet design specifications. In our last published report we detailed how replacement of the PVA with poly(acrylic acid) (PAA) resulted in a major improvement in sphericity due to a greatly increased interfacial tension between the bath and the compound droplet, relative to the use of PVA as the bath additive. P{alpha}MS mandrels produced using PAA in the bath along with slow curing to suppress Marangoni convection that was perturbing the mode 10 to 20 symmetry resulted in 2-mm-diameter P{alpha}MS shells with mode 2 out-of-round{sup 10} (OOR) of {approx}0.5 {micro}m (as well as non-concentricity (NC) < 1%) which meet the capsule design requirements. A representative set of equatorial traces produced by our AFM-based Spheremapper along with the computed power spectrum is shown in Figure 1 for an average shell. Although the power spectrum is at or below the design specification at nearly all modes one can see in the traces some degree of roughness which manifests itself at the very high modes in the power spectrum.