Target Injection and Fabrication Possibilities for Fast Ignitor IFE

1. Target Injection and Fabrication Possibilities for Fast Ignitor IFE R.B. Stephens and D.T. Goodin General Atomics San Diego, CA 92121 • High gain • Relaxed symmetries • Low-cost targets?? (IFSA Paper #1102)

2. Separation of compression and ignition gives flexibility Driver assembles fuel ~1 MJ, 10 ns laser, Z-pinch, or HIB Direct or indirect

3. Separation of compression and ignition gives flexibility • Driver assembles fuel • ~1 MJ, 10 ns • laser Z-pinch, or HIB • Direct or indirect • Ignitor heats minimal volume of DT • ~100kJ, 10 ps • ~20 µm dia to ~10 keV • Fuel can vary • DT • DD • Low z compound

4. Central Hot Spot targets ignite using spherically converging shock waves Precision spheres and uniform ablator thicknesses so waves converge Smooth ablator to avoid breakup Smooth ice to minimize mixing Fast ignition targets ignite from the outside Want to avoid a “hot spot” in the compression - reduces burn efficiency Pure DT fuel in the ignition volume Uniformly dense fuel in the assembled target Compact shape Need to know where the target assembles, and provide reliable access to it Breakup could be good Mixing should be encouraged Targets don’t need highly spherical symmetry

5. The original concept is very simple  must have approximate spherical symmetry, requires additional laser to create tunnel for ignitor beam - but ignition volume is clouded by blowoff Trend = add protected ignition access closer to the assembled target define ignition volume allow target jitter FI targets concepts are being defined M. Roth, T.E. Cowan, et al. (GSI, LLNL, MSFC, UA-Huntsville) R.B. Stephens, M. Key, et a l, Proceedings of Fusion Summer Study, Snowmass, CO

6. Indirect drive cone in shell concept selected for testing at LLE Was difficult to make (GDP/PAMS) Was even more difficult to assemble tip of cone 20 m from center And cryo-ignition target may be even more difficult - uniform ice layer? ice cover the cone?* thermal control? Be+Cu DT ice Au cone r=3.e-5gcm-3 2 mm Ignition scale Cone Shell Hohlraum Direct drive version is being investigated at Osaka * see poster “Optimizing the strucutre of FI targets,” Stephens, Dahlburg & Hatchett

7. Form DT layers for mass production Processes such as stamping or injection molding Simplifies target construction Layer not dependent on shell thermal properties or shape Allows pure DT shell (eliminate plastic ablator and radiative preheat) Eliminate diffusion fill and layering time Little temperature control needed during fabrication Increased tolerance to heating during injection Possible problems Rougher surface Joint defect Temperature control (can’t use liquid or gas helium to control temperature while storing) Cracking between cone and shell

8. Fast ignition targets can tolerate this approach? Rough surface and join seam encourages mixing More RT sensitive encourages even more mixing Control of ice shape allows incorporation of cone Injection immediately on assembly - no heating problems - minimizes inventory Cone can lead shell on injection - takes the brunt of gas heating & deposition Removal of high z ablator reduces radiation heating

9. Future work Need a real FI target design to get realistic idea of roughness allowed Stamping processes can produce surfaces like? With joins like? Would DT stick to the mold? What are true temperature tolerances? Model heating & stresses during injection