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Target Highlights • Scaling (gain curves) and progress on “hybrid “ targets • Fast ignition scaling and physics • Improved models of fluid instabilities • New “fast ignition” ideas such as impact ignition, “shaped charges”, laser-generated ions, directly with heavy ions… • Targets for high energy density physics • Real progress in target mass production techniques
Overall pathway for HIF target supply has been established Fabricate Capsules DT Fuel Fill DT Fuel Layer Microencapsulation Load capsule in hohlraum Inject/ track Fabricate hohlraum Pressure cell Fluidized bed Multiple advanced manufacturing steps Injector demo experiment 1) Fabricating the spherical capsule 2) Filling the capsule with fuel 7) Assembling the cryo components 3) Cooling the capsule to cryo 8) Accelerating for injection 4) Layering the DT into shell 9) Tracking the target’s position 5) Fabricating the hohlraum case 10) Providing steering/timing info 6) Fabricating the radiators Major advantages: started with DP/ICF experience base, synergism with laser fusion and ZFE programs
Taken together I believe that the progress and directions represented by the target work can have a truly profound effect on heavy ion fusion.
The difficult programmatic problem for heavy ion fusion has always been the high buy-in cost. • This problem has been emphasized at the last two Symposia. • Western Europe, Russia, and Japan have partially solved the problem by joining forces with nuclear physics programs; however, the parameters are not ideal for fusion. • The problem is more serious in the United States because the induction approach is not usually favored for nuclear and particle physics. • Long-term projected costs are also high, e. g. , RPD.
There at least four ways to attack the cost problem • Advancements in beam physics • Improved accelerator engineering and fabrication • Efficient development paths, e. g. , modularity • Target improvements and proper attention to target scaling laws
By exploiting target scaling laws one can dramatically reduce required driver energy • Specific energy, E/(a 3 ), and focused intensity, S E/(a 2 ), are hydrodynamic invariants (a = scale length). • By exploiting this scaling, lasers have been able to do significant HEDP experiments ( >> 10 MJ/g and S >> 10 TW/cm 2) at low E (kilojoules). • Given the increased emphasis on HEDP, can ion accelerators do the same? In principle, Yes! Beam brightness should improve with decreasing scale.
Previously HIF has not scaled well to small size for several reasons • GW power plants have needed large yields => large E (about 7 MJ) because of limitations on chamber rep rate and cost of targets. • Present engineering assumptions in induction linac systems codes limit scaling (for example, thyratron pulsers, rise and fall models, alignment models, voltage models, and lattice design). • To scale to small size, one must do the engineering differently.
D. Callahan’s new gain curve Unlike HEDP targets, alpha range, diffusive processes, etc. set minimum scale size and change scaling behavior.
Things that I would like to see at the next meeting: • Extension of fusion target scaling to sub-megajoule levels (say 0. 7 MJ) -- perhaps using polar direct drive (An Engineering Test Facility and HEDP (> 10 MJ/g) rather than a 1 GWe power plant guide driver scale & engineering and beam science) • Evaluation of the new ideas on fast ignition, especially heavy ion fast ignition. • Elimination of dual-energy requirement • Progress in changing the rules that preclude certain types of research needed for both HEDP and fusion. • More thought about development path issues
Progress in targets and interest in HEDP offer a real opportunity to reduce the driver energy by an order of magnitude. Let’s seize the opportunity.
Development path desiderata • Lead to an optimal full-scale driver • Address critical issues early and inexpensively • Enable HEDP, including target physics, early and inexpensively • Make technical sense
Advances in beam physics may allow HIF to operate in a more economical parameter regime. Old Cost Recent Acceleration Voltage