Development of High Quality Poly(α-Methylstyrene) Mandrels for NIF

Recently, we developed a new method for making spherical poly(α-methylstyrene) (PαMS) mandrels. The process utilizes a small amount (<0.1wt%) of high-molecular-weight poly(acrylic acid) (PAA) in the suspending medium, which substantially increases the interfacial tension during curing relative to methods using poly(vinyl alcohol) (PVA) and yields extremely round capsules. The PAA is also beneficial for centering of the core water, leading to exceptionally concentric capsules. However, fully cured capsules made by this method displayed a significant level of high frequency surface debris that became especially problematic when the mandrels were subsequently overcoated. To solve this problem we examined the use of PAA in conjunction with PVA in order to reduce these surface features, and explored numerous variations of concentration and timing of the PVA addition. The optimum conditions were found to be initial use of PAA for centering and symmetry of the mandrels, followed by removal of the PAA medium, washing of the mandrels with water, and finally transfer to PVA solution for completion of the curing cycle. Glow discharge polymer shells made from these mandrels have power spectra that meet the ignition capsule design requirements.