A wide variety of heavy-ion target designs has been investigated, including indirect-drive, hohlraum/capsule targets that resemble NIC targets. Recently, the emphasis has shifted to direct-drive targets, but to date the analysis of how these targets perform has been based on computation rather than experiment, and the codes have not been benchmarked with experiments in relevant regimes.
CONCLUSION 4-12: The U.S. heavy-ion-driven fusion program is considering direct-drive and indirect-drive target concepts. There is also significant current work on advanced target designs.4 This work is at a very early stage, but if successful may provide very high gain.
• The work in the heavy-ion fusion (HIF) program involves solid and promising science.
• Work on heavy-ion drivers is complementary to the laser approaches to IFE and offers a long-term driver option for beam-driven targets.
• The HIF program relating to advanced target designs is in a very early stage and is unlikely to be ready for technical assessment in the near term.
• The development of driver technology will take several years, and the cost to build a significant accelerator driver facility for any target is likely to be very high.
Current Z-pinch direct-drive concepts utilize the pressure of a pulsed, high magnetic field to implode deuterium-tritium fuel to fusion conditions. Simulations predict that directly using the pressure of the magnetic field to implode and compress the target can greatly increase the efficiency with which the electrical energy is coupled to the fuel as compared with the efficiency of indirect drive from Z-pinch X-ray sources. There is work under way on both classified and unclassified target designs.
CONCLUSION 4-13: Sandia National Laboratories is leading a research effort on a Z-pinch scheme that has the potential to produce high gain with good energy efficiency, but concepts for an energy delivery system based on this driver are too immature to be evaluated at this time.
4 Advanced designs include direct-drive, conical X-target configurations (see Chapter 2).