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IFE Chamber Dynamics

ESLI. IFE Chamber Dynamics. Presented by Mark S. Tillack. contributors: F. Najmabadi, A. R. Raffray, S. S. & Bindhu Harilal, D. Blair, A. Gaeris, S. Krasheninnikov (UCSD), C. Olson, T. Renk (SNLA), T. Knowles (ESLI), D. Haynes (UWisc),

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IFE Chamber Dynamics

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  1. ESLI IFE Chamber Dynamics Presented by Mark S. Tillack contributors: F. Najmabadi, A. R. Raffray, S. S. & Bindhu Harilal, D. Blair, A. Gaeris, S. Krasheninnikov (UCSD), C. Olson, T. Renk (SNLA), T. Knowles (ESLI), D. Haynes (UWisc), J. P. Sharpe (INEEL), J. Latkowski, D. Blackfield (LLNL) DOE Budget Planning Meeting Germantown, MD March 12, 2002

  2. Background •Following target explosions, several distinct stages of chamber response occur:1. Prompt transport of energy through and deposition into materials (ns-ms) 2. Radiation fireball & shock propagation, mass ejection from walls (1-100 ms) 3. Afterglow plasma & transport processes (1-100 ms) 4. Liquid wall dynamics (ms-s) 5. Long-term changes in materials (days-months) •A better understanding of chamber physics is neededin order to make progress on key IFE technology issues:8 Wall protection8 Chamber clearing for target and driver injection •This presentation focuses on the underlying science of IFE chambers in a generic sense (i.e., without ties to a specific chamber design concept), using results from OFES IFE Technology, DP-HAPL and ARIES-IFE programs

  3. Outline 1. Surface modification from pulsed ion flux2. Fireball dynamics in a gas-protected chamber3. Plume ejection dynamics4. Aerosol and dust generation and transport 5. Magnetic diversion of expanding plasma6. Ion stopping by beam-plasma instabilities

  4. 1 m CH +300 Å Au Energy Split CH Foam + DT .195 cm X-rays DT Fuel .169 cm DT Vapor 0.3 mg/cc .150 cm Neutrons Ions CH foam  = 20 mg/cc Total Details of target emissions have a strong impact on chamber and wall responses NRL Direct-Drive Target Direct Drive Target (MJ) High Yield DD Target Indirect Drive Target (MJ) 2.14 (1%) 6.07 (1%) 115 (25%) 109 (71%) 279 (70%) 316 (69%) 43 (28%) 112 (28%) 26.5 (6%) 154 397 458 X-ray spectra LLNL/LBNL HIF Target

  5. Time-of-flight spreading allows significant thermal penetration during energy deposition NRL direct drive target spectrum (154 MJ) Ion power at chamber wall (R=6.5 m) 100 ns Photon and ion attenuation in C and W slabs (1 ms~1 mm thermal penetration depth)

  6. Modeling and simulation experiments are being used to improve our understanding of chamber dynamics Facilities: Modeling tools: Pulsed ion sources (e.g., RHEPP) Pulsed x-ray sources (e.g., Z) Pulsed e-beam facilities (DTRA) Lasers: 1–2 J materials response, laser propagation diagnostic development 100–200 J rep-rated chamber dynamics 1–2 kJ IRE (integrated effects) Ignited targets (ETF) Rad/hydro (LASNEX, BUCKY) Surface responses (SRIM, Ablator) Mass ejection and recondensation Gasdynamics (CFDSTARS) Ion transport (LSP) Atomic physics

  7. 1. Surface modification from pulsed ion flux

  8. Ion exposure experiments are being performed at the RHEPP pulsed ion source • 0.5 MeV ions C+, H+ • Range ~ 1 mm • 150-300 ns pulse • Thermal penetration ~ microns • 10 J/cm2 fluence • Similar to IFE • Repeating • 1000 shots max Magnetically confined Anode Plasma IFE Materials Test Matrix: • W alloys • C-graphite, Ceramic fiber composites • Innovative architectures e.g., fiber flocked, functionally graded, nano-engineered • Flibe

  9. Severe carbon erosion and roughening are observed above 2–3 J/cm2 Ablation Step (microns) Ra (treated) Ra (untreated) 100 ESLI engineered wall exhibits much less net erosion • Each pulse is spread over 15x more area • The ablated material may redeposit on the nearby fibers: recycling • Thermal penetration into vertical fibers may be providing effective cooling on this time scale 10 Ion Beam Fluence (J/cm2) 1 Specimen fractured to reveal interior 0.1 0 1 2 3 4 5 6 Mechanically polished Poco graphite exposed to 75 pulses of 70% C/30% H beam at average dose of 5.5 J/cm2 Step measurement accuracy ~ 0. 4 µm reached below ~ 3 J/cm2 Profilometer scan across interface: ~ 20 micron step (0.27 µm/pulse) Ra (original) = 0.23 microns Ra (treated) = 3.6 microns

  10. IBEST (Ion Beam Surface Treatment) uses intense ion beams to melt and modify surfaces Melt Region • 500-750 keV N+ ions • Range ~ 2–10 mm • 109 K/s cooling rate due to thermal diffusion • 2–8 J/cm2 fluence to melt IONS Cooling by Thermal Diffusion Ion Range Tribometer wear tracks in Pt-Ti cosputtered layer without and with surface treatment (2000 wear cycles) T. Renk et al., “Improvement of surface properties by modification and alloying with high-power ion beams,” Phys. Plasmas 5(5), May 1998.

  11. 2. Fireball dynamics in a gas-protected chamber

  12. The dominant threat for the indirect-drive target is from soft x-rays created by debris ions • Simulating the protection of a dry first wall with a buffer gas requires: • Radiative hydrodynamics (BUCKY) • EOS/opacity data from the coronal to the collisional regimes (IONMIX) This would be deposited in the first micron of the wall effectively instantaneously, causing the graphite to sublimate at a rate incompatible with rep-rated reactor concepts. Nearly half of the 115MJ of prompt x-ray energy comes in the form of sub-keV photons

  13. For the HIB target in a 4.5m radius graphite chamber, 1 Torr of Xe is sufficient to prevent first wall sublimation X-ray energy (MJ) Ion energy (MJ) Gas 105 19 Wall 10 6 (knock-ons only) • The simulation proceeds by instantly depositing the prompt target x-rays through the gas and the wall. • The ions from the target then traverse the ionized gas, depositing their energy through a stopping power formalism, while the gas dynamics are tracked using 1d Lagrangian radiative-hydrodynamics. Ion temperature (eV) contours from BUCKY simulation Fireball forms from captured x-ray and ion energy Fireball propagates and slowly re-radiates energy, allowing wall to conduct energy away from surface, avoiding sublimation HIB target output energy deposited in the gas and wall of a 4.5m radius graphite walled chamber filled with 960mTorr of Xe starting at 1000C.

  14. 3. Plume ejection dynamics

  15. Processes present in IFE mass ejection and transport are analogous to laser micromachining • Energy absorption in surface • Prompt thermal response of surface • Liquid hydrodynamics • Evaporation • Unsteady gas dynamics (including chamber environment) • Radiation transport • Condensation • Laser-plume interaction

  16. Table-top experiments with extensive diagnosticsare being developed to explore chamber responses

  17. Modeling and experiments are being performed for both liquid and solid surfaces 1 . E + 1 9 1 . E + 1 8 1 . E + 1 7 1 0 1 0 0 1 0 0 0 1 0 0 0 0 Electron density of Si ablation plume measured by Stark broadening at 390 nm, 1e9 W/cm2 0.15 Torr Electron Density [cm-3] Time [ns] 100 Torr Expansion velocity = 4.5e6 cm/s (300 eV)

  18. 4. Aerosol and dust generation and transport

  19. Aerosol and dust generation and transport are important for both chamber clearing and safety Convective Diffusion and Transport Particle Growth Rates Growth Rate Models: Nova dust Homogeneous Nucleation (Becker-Doring model) Condensation Growth Coagulation where the coagulation kernel is given by

  20. Opportunities and challenges for IFE research on aerosol and dust generation and transport Formation Rate and Size of Pb droplets in an IFE System • Computational improvements to solve stiff integro-differential transport equations • Plasma effects on dust growth and transport mechanisms (e.g., dusty plasmas) • In-situ particle diagnostics for determining fundamental mechanisms of nucleation and growth in fusion, space, and industrial plasma environments • Development of nanoparticle generation systems for industrial and medical uses SIRENS simulator vs. TopGun model Cu plasma 5.2 kJ, 120 ms 450 mg particulate 70% melt blowoff typical value for a bubble chamber J.P. Sharpe, B.D. Merrill, D.A. Petti, "Modeling of Particulate Production in the SIRENS Plasma Disruption Simulator," J. Nuclear Materials, vol.290-293, 1128-1133 (2001).

  21. 5. Magnetic diversion of expanding plasma

  22. Magnetic deflection is being studied forprotection of the first wall against ions Three configurations are currently under consideration: • Uniform field • Mirror arrangement • Cusp arrangement Cusp configuration is simply a mirror with the field reversed in one of the coils. Uniform field configuration would require more magnets but lower (~2 T) fields. L. A. Booth and T. G. Frank, “Commercial Applications of Inertial Confinement Fusion,” LA-6838-MS, May 1977.

  23. PIC simulations have been initiated using LSP code (MRC) developed for HIF • Ions only in these two movies • Field strength ~8 T, 14 m diameter coils • Red particles are DT (mass=2.5, charge=1) at 250 keV; blue particles are alphas at 1 MeV; Total plasma energy is 113 MJ Mirror Cusp

  24. Inclusion of electrons is computationally very challenging, but necessary • Red particles are DT (mass=2.5, charge=1) at 250 keV; green particles are alphas, blue particles are electrons • Key issues include stability, collisions, charge exchange, Bremsstrahlung & synchotron radiation, cost of magnets & shielding, recirculating power for magnet cooling

  25. 6. Ion stopping by beam-plasma instabilities

  26. Residual plasma persists longer than the dwell time Chamber gas/plasma temperature stops falling below ~1 eV for Lrad(t)~10–25 W-cm3 Recombination becomes ineffective below npl~1019/m3 Characteristic plasma recombination time, trec

  27. Impact of residual plasma on ion stopping •For reasonable chamber gas density the impact of binary collisions on stopping of energetic (~ 1 MeV) ions is small (e.g.,for H on Xe at 10 mTorr,dE/dx=87 MeV-cm2/g = 0.05 MeV/m) •However, collective effects of the interactions of the beam of energetic ions with residual plasma can significantly alter the population of energetic ions •Total number of fast ions per pellet, ni-fast~1020 m–3, results in average ion beam density ni-beam~1016 m–3 •During pellet explosion the electron temper-ature of residual plasma can be quickly heated up by electron heat conduction, so that the electron temperature of residual plasma exceeds the ion temperature.

  28. • Free expansion into an ambient plasma is also a subject of astrophysical interest D. S. Spicer, R. W. Clark and S. P. Maran, “A model of the pre-Sedov expansion phase of supernova remnant-ambient plasma coupling and x-ray emission from SN1987A,” The Astrophysical Journal 356 (1990) 549. Impact of residual plasma on ion stopping •For ni-beam~1016 m–3 and, npl~1018 m–3, we find gi-beam~108 s–1 •Assuming the effective collision frequency of the beam with residual plasma is of the order of gi-beam , we find a crude estimate of stopping distance of fast ions caused by collective effects, Li-beam: • •Further study of the impact of collective effects on fast ion stopping is needed: • – a more accurate description of the evolution of residual plasma parameters • – a more detailed evaluation of collective interactions of fast components (both electron and ion) with the background gas/plasma

  29. Closing Remarks • IFE chamber dynamics encompasses a wide variety of phenomena with numerous opportunities for fundamental scientific investigations • A better understanding of IFE chamber dynamics is needed in order to make progress toward an IFE power plant • IFE chamber dynamics shares many features in common with MFE and non-fusion sciences • A multi-institutional program of theory, modeling and experiments is being developed through a combination of DP & OFES support

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