1. November 20, 2002 A. R. Raffray, et al., Thin Liquid Wall Behavior under IFE Cyclic Operation 1 Thin Liquid Wall Behavior under IFE Cyclic Operation A. R. Raffray 1, S. I. Abdel-Khalik 2, D. Haynes 3, F. Najmabadi 4, J. P. Sharpe 5 and the ARIES Team 1 Mechanical and Aerospace Engineering Department and Center for Energy Research, University of California, San Diego, EBU-II, Room 460, La Jolla, CA 92093-0417 2 School of Mechanical Engineering, Georgia Institute of Technology, Atlanta, GA 30332-0405 3 University of Wisconsin, Fusion Technology Institute, 1500 Engineering Drive, Madison, WI 53706-1687 4 Electrical and Computer Engineering Department and Center for Energy Research, University of California, San Diego, EBU-II, Room 460, La Jolla, CA 92093-0417 5 Fusion Safety Program, EROB E-3 MS 3860, INEEL, Idaho Falls, Idaho 83415-3860 15th Topical Meeting on the Technology of Fusion Energy Washington, D.C. November 20, 2002

2. November 20, 2002 A. R. Raffray, et al., Thin Liquid Wall Behavior under IFE Cyclic Operation 2 Outline IFE chamber operating conditions Thin Liquid Wall Configuration –Attractiveness and key issues Film Establishment and Coverage –Wetted wall –Forced film flow Film Condensation Aerosol formation and behavior –Aerosol source term (including explosive boiling estimate) –Aerosol formation and transport analysis –Design windows (including driver and target constraints) Concluding Remarks

3. November 20, 2002 A. R. Raffray, et al., Thin Liquid Wall Behavior under IFE Cyclic Operation 3 IFE Operating Conditions Cyclic with repetition rate of ~1-10 Hz Target injection (direct drive or indirect drive) Driver firing (laser or heavy ion beam) Microexplosion Large fluxes of photons, neutrons, fast ions, debris ions toward the wall -possible attenuation by chamber gas Target micro- explosion Chamber wall X-rays Fast & debris ions Neutrons Example of Direct-Drive Target (NRL) (preferred option for coupling with laser driver) DT Vapor 0.3 mg/cc DT Fuel CH Foam + DT 1  m CH +300 Å Au.195 cm.150 cm.169 cm CH foam  = 20 mg/cc Example of Indirect-Drive Target (LLNL/LBLL) (preferred option for coupling with heavy ion beam driver)

4. November 20, 2002 A. R. Raffray, et al., Thin Liquid Wall Behavior under IFE Cyclic Operation 4 Energy Partitioning and Photon Spectra for Example Direct Drive and Indirect Drive Targets Energy Partitions for Example Direct Drive and Indirect Drive Targets Photon Spectra for Example Direct Drive and Indirect Drive Targets Much higher X-ray energy for indirect drive target case (but with softer spectrum) Basis for example wetted wall analysis presented here (More details on target spectra available on ARIES Web site: http://aries.ucsd.edu/ARIES/) (25%) (1%)

5. November 20, 2002 A. R. Raffray, et al., Thin Liquid Wall Behavior under IFE Cyclic Operation 5 IFE Thin Liquid Wall Configuration Key processes:  Thin film dynamics  Condensation  Aerosol formation and behavior  These are assessed here with Pb and flibe as example fluids Injection from the back Condensation Ablation PgTgPgTg Film flow Photons Ions In-flight condensation Advantages of decoupling functions: –Armor function to accommodate X-ray and ion threat spectra provided by renewable liquid film for longer lifetime –Structural and energy recovery functions provided by solid blanket at the back for high efficiency Major issues: –Film establishment and coverage Film dynamics Injection method Geometry effects Recondensation –Ablated material and chamber clearing requirements Ablation processes Film condensation Aerosol formation and behavior Driver and target requirements

6. November 20, 2002 A. R. Raffray, et al., Thin Liquid Wall Behavior under IFE Cyclic Operation 6 Film Dynamics Two Injection Methods Considered -Radial injection through a porous first wall ( “wetted wall” design) - Forced flow of a thin liquid film tangential to a solid first wall (“forced film” design) Critical Questions Include: (1) Can a stable liquid film be maintained on the upper section of the chamber? (2) Can the film be re-established over the entire cavity surface prior to the next target explosion? (3) Can a minimum film thickness be maintained to prevent dry patch formation and provide adequate protection during the next target explosion. These Questions are Being Addressed through Complementary Modeling and Experimental Investigations -Example results illustrated here

7. November 20, 2002 A. R. Raffray, et al., Thin Liquid Wall Behavior under IFE Cyclic Operation 7 Example of Wetted Wall Investigation Modeling simulation of 3-D evolution of liquid film surface based on: -Liquid injection velocity through porous wall -Surface disturbance amplitude, configuration and mode number -Surface inclination angle -Liquid properties -Effect of film evaporation and/or condensation Results used to develop “generalized charts,” showing effects of these variables on: -Frequency of liquid drop formation and detachment, -Size of detached droplets -Minimum film thickness prior to droplet detachment Example results for 700 K Pb with initial thickness of 1.0 mm and injection velocity of 1.0 mm/s Random initial perturbation with maximum amplitude of 1.0 mm applied beginning of the transient In this case, droplet detachment occurs ~0.38 s after initial perturbation t = 0.38 s t = 0.37 s t = 0.32 s t = 0.35 s Poster presented during Tue. afternoon session (1.27)

8. November 20, 2002 A. R. Raffray, et al., Thin Liquid Wall Behavior under IFE Cyclic Operation 8 Examples of Forced Film Investigation Film detachment most likely to occur on downward facing surfaces in upper part of chamber -Could interfere with beam propagation and/or target injection Experimental study to determine film detachment distance as a function of: -Wetting and non-wetting surfaces -Initial film thickness (1.0 to 2.0 mm) -Film injection velocity (1.9 to 11.0 m/s) -Inclination angle (0º to 45º) Poster presented during Tue. afternoon session (1.31) Film detachment distance vs. Froude number for horizontal downward-facing surfaces wetting surface Non-wetting surface 1.5 mm 2.0 mm 1.0 mm Film thickness: Flow of 1.5 mm thick film with a 5.0 m/s velocity around 25.4 mm dia., 2.4 mm high cylindrical “port.” Experimental study of behavior of thin liquid films flowing around cylindrical obstacles, typical of beam and target injection ports -Such obstacles will pose significant challenge to designers -Efforts underway to examine behavior of thin films flowing past "streamlined" obstacles.

9. November 20, 2002 A. R. Raffray, et al., Thin Liquid Wall Behavior under IFE Cyclic Operation 9 Film Condensation Rate is Fast Characteristic time to clear chamber, t char, based on condensation rates and Pb inventory for given conditions For higher P vap, t char is independent of P vap -Probably more limited by heat transfer effectiveness As P vap decreases and approaches P sat, t char increases substantially Typically, IFE rep rate ~ 1–10 Time between shots ~ 0.1–1 s P vap prior to next shot ~(1-10)P sat Can be controlled by setting T film Of more concern is aerosol generation (in-flight condensation) and behavior Example Analysis of Pb Vapor Film Condensation in a 10-m Diameter Chamber

10. November 20, 2002 A. R. Raffray, et al., Thin Liquid Wall Behavior under IFE Cyclic Operation 10 Processes Leading to Vapor/Liquid Ejection Following High Energy Deposition Over Short Time Scale Energy Deposition & Transient Heat Transport Induced Thermal- Spikes Mechanical Response Phase Transitions Stresses and Strains and Hydrodynamic Motion Fractures and Spall Surface Vaporization Heterogeneous Nucleation Homogeneous Nucleation (Phase Explosion) Material Removal Processes Expansion, Cooling and Condensation Surface Vaporization Phase Explosion Liquid/Vapor Mixture Spall Fractures Liquid Film X-Rays Fast Ions Slow Ions Impulse yy xx zz

11. November 20, 2002 A. R. Raffray, et al., Thin Liquid Wall Behavior under IFE Cyclic Operation 11 High Photon Heating Rate Could Lead to Explosive Boiling Photon-like heating rate Ion-like heating rate Effect of free surface vaporization is reduced for very high for heating rate (photon-like) Vaporization into heterogeneous nuclei is also very low for high heating rate From K. Song and X. Xu, Applied Surface Science 127- 129 (1998) 111-116 Rapid boiling involving homogeneous nucleation leads to superheating to a metastable liquid state The metastable liquid has an excess free energy, so it decomposes explosively into liquid and vapor phases. -As T/T tc increases past 0.9, Becker- Döhring theory of nucleation indicate an avalanche-like and explosive growth of nucleation rate (by 20-30 orders of magnitude)

12. November 20, 2002 A. R. Raffray, et al., Thin Liquid Wall Behavior under IFE Cyclic Operation 12 Photon Energy Deposition Density Profile in Flibe Film and Explosive Boiling Region Cohesion energy (total evaporation energy) 2.5 Evap. region 10.4 2-phase region Sensible energy (energy to reach saturation) Sensible energy based on uniform vapor pressure following photon passage in chamber and including evaporated Flibe from film 0.9 T critical 4.1 Explo. boil. region Bounding estimates of aerosol source term: (1)Upper bound: the whole 2-phase region; (2)Lower bound: explosive boiling region Posters on flibe properties presented during Tue.& Wed. afternoon sessions (1.38 & 2.36)

13. November 20, 2002 A. R. Raffray, et al., Thin Liquid Wall Behavior under IFE Cyclic Operation 13 Spherical chamber with a radius of 6.5 m Surrounded by liquid Pb wall Spectra from 458 MJ Indirect Drive Target Explosive boiling source term (2.5  m, lower bound) Analysis of Aerosol Formation and Behavior Region 1 From the analysis, aerosol formation could be a key issue and need to be further addressed Driver and target constraint also need to be more accurately defined Appreciable # and size of aerosol particles present after 0.25 s ~10 7 -10 9 droplets/m 3 with sizes of 0.05-5  m in Region 1 Preliminary estimate of constraints: -Target tracking based on 90%beam propagation -Heavy ion driver based on stripping with integrated line density of 1 mtorr for neutralized ballistic transport

14. November 20, 2002 A. R. Raffray, et al., Thin Liquid Wall Behavior under IFE Cyclic Operation 14 Spherical chamber with a radius of 6.5 m Spectra from 458 MJ Indirect Drive Target Explosive boiling source term (5.5  m) Analysis of Aerosol Formation and Behavior for Flibe Aerosol size and # after 0.25 s -10 7 -10 9 droplets/m 3 with sizes of 0.3-3  m -Exceeds driver limit Again, from this analysis, aerosol formation could be a key issue Needs to be addressed by future effort Oral presentation during Thu. morning session Region 1 Target tracking constraint Neutralized ballistic transport: stripping constraint

15. November 20, 2002 A. R. Raffray, et al., Thin Liquid Wall Behavior under IFE Cyclic Operation 15 Concluding Remarks Wetted walls provide possibility of high efficiency and renewable armor Key issues are film establishment and chamber conditions prior to next shot Experimental and modeling effort under way to provide generalized charts for designing film injection system: -Wetted wall (droplet detachment, minimum film thickness…) -Forced film flow (film detachment, beam port obstacles...) High energy deposition rate of X-rays would lead to explosive boiling - Provide bounding estimates for aerosol source term Aerosol modeling analysis indicate substantial # and size of droplets prior to next shot for both Pb and FLiBe - Preliminary estimates of constraints for indirect-drive target and heavy ion driver - Marginal design window (if any) Future effort: -Completing generalized charts on film dynamics -Better understanding aerosol source term and behavior -Confirmation of target and driver constraints

16. November 20, 2002 A. R. Raffray, et al., Thin Liquid Wall Behavior under IFE Cyclic Operation 16 Other ARIES-IFE Related Presentations at 15 th TOFE S. Shin, S. I. Abdel-Khalik, D. Juric and M. Yoda, ”Effects of surface evaporation and condensation on the dynamics of thin liquid films for the porous wetted wall protection scheme in IFE reactors,” Tue. afternoon poster session, 1.27 J. K. Anderson, M. Yoda, S. I. Abdel-Khalik and D. L. Sadowski, “Experimental studies of high-speed liquid films on downward-facing surfaces,” Tue. afternoon poster session, 1.31 M. Zaghloul, D. K. Sze and R. Raffray, “Thermo-physical properties and equilibrium vapor-composition of lithium fluoride-beryllium fluoride (LiF/BeF 2 ) molten salt,” Tue. afternoon poster session, 1.38 L. El-Guebaly, P. Wilson, D. Henderson, L. Waganer, R. Raffray and the ARIES Team, “Radiological issues for thin liquid walls of ARIES-IFE study, Tue. afternoon poster session, 1.51 J. P. Sharpe, B. J. Merrill and D. A. Petti, “Aerosol production in IFE chamber systems,” Thu. Morning oral session L. El-Guebaly, P. Wilson, D. Henderson, A. Varuttamaseni and the ARIES Team, “Feasibility of target material recycling as waste management alternative, “ Thu. Morning oral session M. Zaghloul, “Ionization equilibrium and thermodynamic properties of high-temperature FLiBe vapor in wide range of densities,” Wed. afternoon poster session, 2.36