fusion devices at the University of Wisconsin. A nanoengineered tungsten wall material showed an encouraging ability to mitigate helium retention. Experiments showed that cyclic heating in the IFE chamber mitigates helium retention.
The spectrum output issues associated with the RTL/Z-pinch system are unique to this approach. The mass of material in this assembly is much greater than in any other concept, leading to greater recycling requirements. Further, the interaction of the fusion output with the RTL structure could lead to unique problems with the formation of shrapnel and debris. These problems are not presently understood but appear to require a thick liquid-wall chamber.
The primary concern of this panel with regard to ICF target fabrication relates to the technical feasibility of various proposed fabrication methods and the remaining technical risks and uncertainties associated with these methods. The question of whether the targets can be made cost-efficiently for a power plant is beyond the purview of this panel and is addressed by the National Research Council’s IFE committee. Some promising approaches are discussed below.
Microfluidic Methodologies for Manufacturing Targets
The polymer shell that contains the DT fuel for DD laser and heavy-ion-beam fusion is proposed to be manufactured using a microfluidic droplet formation method.22 This is an established technology that is used to make ICF capsules for current DD and ID experiments. The principle is to flow three immiscible fluids coaxially through two nozzles where the Rayleigh-Plateau instability that occurs in the region where they intersect produces individual droplets. Each droplet is an emulsion consisting of a thin shell of water surrounding a spherical oil droplet; these droplets are collectively immersed in oil. The thin shell of water contains the polymer precursors that form the plastic capsule. The final phase of the production process is to remove the fluids using supercritical drying.
This process has a very high production rate that is needed for a fusion energy program. However, the repeatability and precision of the process must be improved if the process is to be a viable option for an energy program. (The repeatability of the current process does not ensure that each capsule meets the required
22 A. Nikroo, General Atomics, “Technical Feasibility of Target Manufacturing,” presentation to the panel on July 8, 2011; see also Utada et al., 2007.