Ultrasmooth plasma polymerized coatings for laser fusion targets

Abstract

Coatings for laser fusion targets were deposited up to 135 μm thick by plasma polymerization onto 140 μm diam DT filled glass microspheres. Ultrasmooth surfaces (no defect higher than 0.1 μm) were achieved by eliminating particulate contamination. Process generated particles were eliminated by determining the optimum operating conditions of power, gas flow, and pressure, and maintaining these conditions through feedback control. From a study of coating defects grown over known surface irregularities, a quantitative relationship between irregularity size, film thickness, and defect size was determined. This relationship was used to set standards for the maximum microshell surface irregularity tolerable in the production of hydrocarbon or fluorocarbon coated laser fusion targets.

Fabrication of Graded Germanium-Doped CH Shells

“…The density used for CH is 1.08-1. 10. These values give a very good match of the calculated curve with normalized transmission curve for the outer CH layer.…”

“…9,10 To distinguish between mandrel defects and possible agitation induced defects, mandrels from several different batches were coated in the same coating run. We examined dozens of mandrel batches using shorter (~ 6-7 day, ~ 70 µm thickness) coating runs.…”

Fabrication of Surface Bumps on a Capsule to Simulate Fill Tube Mass Defects

“…The gas flows were 0.3 sccm for trans-2-butene and 10 for hydrogen. The chamber pressure was controlled to 98 mTorr and the discharge power was 10 watts (3,6). The rate of coating at this position deposited a 3 µm bump in 6.33 hours…”

“…The bumps specified were to be roughly gaussian in shape, from 60 to 40 µm in diameter and from 1 to 10 µm high. The approach we used to fabricate the bump was to align a precision aperture to the capsule and coat through the aperture onto the capsule surface using plasma polymer coating technology (3). Previous work used a similar approach to fabricate micro-spot flat targets with various dopants for plasma temperature and stability measurements (4).…”

Adapting the Decomposable Mandrel Technique to Build Specialty ICF Targets

“…A shell of poly(α-methyl styrene) (PAMS) produced by microencapsulation is overcoated with plasma polymer (CH). 4 This composite shell is then heat treated at 300 °C to decompose the PAMS to gaseous monomer which diffuses through the thermally more stable plasma polymer shell to leave a shell which replicates the initial mandrel.…”