Opportunities and Issues for IFE Chamber Science

1. Opportunities and Issues for IFE Chamber Science Jeff Latkowksi, Wayne Meier Fusion Energy Program, LLNL Per F. Peterson, Philippe Bardet, Haihua ZhaoDepartment of Nuclear Engineering University of California, Berkeley Heavy Ion Fusion Science VNL Program Advisory Committee Meeting Aug. 9-10, 2006 Livermore, CA

2. Outline • Thick liquid wall chambers for IFE • Near-term opportunities • Preparing for an experimental test facility • Connecting to NIF

3. Thick liquid wall (TLW) chambers have beenthe focus of chamber research for HIF • Potential advantages are well known: • Chamber structures experience a much lower rate of damage  may last for plant lifetime (>30 years) • 14 MeV neutron source (~$1B) not required  existing or slightly modified steels can be used • Chambers can be much more compact  improves HI focusing • TLW also protects from short range target emission and shock due to first surface ablation • Most fusion energy deposited directly in the coolant  efficient heat transport • Have high tritium breeding efficiency

4. The key issues can be summarizedin three primary categories • Issues related to repetitive nature of IFE, including liquid wall response and recovery of chamber conditions between pulses (reformation of protective liquid configuration, clearing of drops and vapor that could interfere with next shot). • Issues related to shock mitigation, including ability of multi-layer thick liquid wall configurations to attenuate shocks and thus protect the structural wall from possible damaging effects of shocks. • Issues related to use of molten salt (preferred liquid), including material compatibility (corrosion), target debris transport and removal, tritium recovery, heat transport and power conversion.

5. Recent past R&D has focused on fundamental understanding and key issues • Hydrodynamic scaling • High quality jets needed along beam paths • Disruption and re-establishment of liquid protection • Condensation and vacuum recovery • Shock propagation through jet array • New schemes, e.g., vortex flow, that may permit higher rep-rate • Interface issues and integrated design studies, e.g., Robust Point Design

6. Near-term opportunities • Re-engage Universities for small scale experiments • Focus on schemes compatible with lower cost development path • Small effort on system integration to assure coupling of development in targets, driver, and focusing schemes

7. Scaled water experiments have demonstrated multiple liquid configurations of interest for HIF UCB Re = 100,000 High-Re Cylindrical Jets Vortex Layers for Beam Tubes Oscillating Voided Liquid Slabs

8. Large liquid vortices could enable thick-liquid, high-rep-rate, lower yield HIF options Example: Chamber volume: 80m3 Liquid volume: 28m3 Open fraction of solid angle: 2.4%

9. UCB has performed detailed measurements of turbulence and surface topology in vortex beam tubes

10. A series of scaled experiments were constructed at UCB to provide proof of principle for large vortex generation • A first-generation test device was fabricated from a short segment of cylindrical pipe (22.5-cm diameter) • Eight pressurized plenums provided blowing flow • Perforations between injection plenums provided suction • Asuction = 2Ainjection • End walls produced modest non-ideality

11. Liquid accumulated during startup was cleared in the first-generation device t = 2.0 sec t = 7.0 sec • The first viability issue for large-vortex flows is removing excess liquid during startup • UCB experiments demonstrate that this can be done by providing sufficient suction area • After startup, flow dumps on suction drains can be closed, and pressure recovery can be achieved • Reduce pumping power • Increase layer thickness t = 14.0 sec stable layer established

12. A large variable recirculation flow loop was constructed Flow meter • Pump is rated for 500-gpm at 300-ft of head • Thanks to the frequency controller,the flow rate can be accurately controlledat any flow rates up to 800-gpm Manifold Nozzle Frequency controller 1000 liter tank 50 hp pump

13. Larger scale facilities will be needed prior to ETF (could begin prior to ignition if funding available) • Hydraulics Test Facility – Demonstrate the type of flow configurations needed for TLW chambers at ~1/4 scale. Simulant fluid (e.g., water) used to minimize costs. Facility would simulate (e.g., by using chemical detonations) flow disruption by fusion energy pulses to study chamber clearing. Also used to study/validate shock mitigation techniques. • Chamber Dynamics Test Facility – Study vaporization/condensation dynamics of molten salt. Focus on aspects unique to molten salt and cannot be simulated in the hydraulic test facility. • Molten Salt Test Loop(s) – Address issues related to use of molten salts in fusion applications: corrosion, transport & recovery of target debris, transport and recovery of tritium. • Heat Transfer Component Facilities – Develop/demonstrate compact, efficient heat exchangers and power cycle components using molten salt coolants. Applicable to IFE, MFE and fission, including hydrogen production.

14. NIF will benefit from chamber science work and spin-backs are possible • First opportunity for test with prototypical target emissions • Experiments to validate chamber response models • First opportunity for neutron isochoric heating experiment (disassembles jets in some TLW designs) • IFE analyses tools will be improved and can be used for NIF experiment planning • X-ray and debris transport and deposition • Surface heating, ablation, shocks • Liquid motion, condensation, etc. • Neutron heating, neutron activation

15. Neutron isochoric heating can be an important issue for the NIF • Neutron isochoric heating will first be experienced on NIF • Can drive debris and shrapnel threats to the final optics(e.g., He-filled cryotubes was the original design) • Understanding of the liquid response to isochoric heating is a critical issue for TLW IFE: • liquid break-up • droplet formation • chamber clearing Can ion beams be used as near-term surrogate and assist in these issues prior to high-yield shots on NIF?

16. Target drop experiment on the NIF? • One could think about “dropping” a target rather than holding it on the target positioner • Would greatly reduce the mass sitting near the target, and thus, debris and shrapnel issues • Translates into reduced debris loading on diagnostics and final optics – may lead to reduced maintenance needs • Would benefit IFE along path of getting past the giggle factor regarding target injection & tracking • Can it be done? • Is this also too many sigmas from the norm?

17. Conclusions • A good start has been made in TLW chamber science for HIF • Opportunities exist for modest cost, near-term R&D to continue progress • A serious IFE effort will require larger scale facilities to address key issues • Chamber science will benefit from experiments that can be fielded on NIF – more work is needed to define in detail • HIF chamber science can also benefit NIF operation

18. BACK-UP SLIDES

19. 2-mm diameter injection hole 4-mm diameter suction hole An second-generation device was constructed, based on the previous experiment • A test device was fabricated from a segment of cylindrical pipe (25.4-cm diameter, 14-cm wide) • Injection and suction holes were fabricated with precision • Eight pressurized plenums provided blowing flow • Perforations between injection plenums provided suction • Asuction = 2Ainjection • End walls produced modest non-ideality

20. Different layer thicknesses have been obtained with Froude number as low as 3 in the second-generation device • d/R = 5% • Fr = U2/gR = 13.6 • Re = UR/d = 5·105 • the layer is inhomogeneous, due to sharp angle of injection Polygon shape layer

21. Dye marking of injection jets revealed their behavior in the layer - further work is required Inline Nozzle Homogeneous Nozzle Rapid prototyping nozzles Free Surface Dye Marking

22. Based on the 2nd generation, a new area of study was commenced on concepts with modular nozzles • To provide improved vortex layer control, distributed injection and suction are needed • The investigation studied injection/suction modulesto study the influence of the injection and suctionanglesthe injection is homogeneously distributed over the circumference • the modules can be built with rapid prototyping

23. Two nozzles with different injection/extraction patterns were built and tested in a ramp experiment • Inline Concept • Homogeneous Concept Ramp experiment allows testing of a modular nozzle section (1/8th circumference).