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PFI

PFI. Objectives of the field: Deliver Proton/Ions beam of matched energy distribution and Intensity to reach Ignition of a pellet compressed by moderate primary driver energy Transport and focus beam energy into the fuel to the required density

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PFI

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  1. PFI • Objectives of the field: • Deliver Proton/Ions beam of matched energy distributionand Intensity to reach Ignition of a pellet compressed bymoderate primary driver energy • Transport and focus beam energy into the fuel to the required density • Develop a system that works under real ICF conditions and is technically compatible with requirements of a power plant Fast Ignition with Protons /Carbon /Heavy Ions Produced by UHI Lasers

  2. PFI- Candidates • Protons / Ions from TNSA (Maxwellian distr.) • Mono-energetic Ions (target chemistry, pulse shape) • Ions from BOA, RPD Mechanisms • Ions driven by SPLA

  3. Objectives of the field: • Deliver Proton/Ions beam of matched energy distributionand Intensity to reach Ignition of a pellet compressed bymoderate primary driver energy • Transport and focus beam energy into the fuel to the required density • Develop a system that works under real ICF conditions and is technically compatible with requirements of a power plant PFI - Status • TNSA: • Protons up to 60 MeV • Sufficient to reach hot spot, dependent on laser intensity • Exponential Spectrum • Problem with source distance, might be beneficial with respect to change in stopping power • High conversion efficiency • 12 % observed (would be 24 %), needs confirmation • Source size, ion depletion, distance must match • Excellent beam quality

  4. PFI Status • BOA /RPD • High energy ions expected (HI-FI possible) • mono-energetic distribution • needs confirmation, long source distance possible • needs circularly polarized light and ultra thin foils • number of available ions, source hydro stability • Beam quality • SPLA • High particle numbers • Hydro tolerance • no need for a high gradient rear surface • Low energy • enough to reach hot spot • Beam quality

  5. PFI Status • Objectives of the field: • Deliver Proton/Ions beam of matched energy distributionand Intensity to reach Ignition of a pellet compressed bymoderate primary driver energy • Transport and focus beam energy into the fuel to the required density • Develop a system that works under real ICF conditions and is technically compatible with requirements of a power plant Source to fuel distance critical (dispersion, focus ability, source size) TNSA has demonstrated 50 µm (15 required) Beam qualilty allows for smaller spots (space charge) Electron sheath shape crucial Lower divergence for Carbon/ HI Ion stopping in ICF plasmas is not known to required detail Ion transport in transport region might cause instabilities

  6. PFI Status • Objectives of the field: • Deliver Proton/Ions beam of matched energy distributionand Intensity to reach Ignition of a pellet compressed bymoderate primary driver energy • Transport and focus beam energy into the fuel to the required density • Develop a system that works under real ICF conditions and is technically compatible with requirements of a power plant Cone guided PFI might be beneficial Relaxed laser focusing/ pointing requirements cone can act as heat shield in direct drive reactor scenarios cone can protect ion source (hydro tolerance to drive pulse)

  7. Proton fast ignition - target stability Shield to protect ion source

  8. Recent and short term experiments • BOA at LANL • Focusing experiments at SNL • large focal spot ion acceleration at RAL • conversion efficiency of 8% at RAL • cone targets at LANL • Experiments on SPLA at LULI Ion acceleration with 10 ps lasers overlap of multiple beams focusing including sheath compensation improvement of conversion efficiency

  9. 100 µm 100 µm 1 D curved foil Z-100 TW: 40J, <1ps, >1019 W/cm2

  10. Elaser=18.7 J, I=1x1019 W/cm2, Δτ=600 fs HD RCF Flared Flat-Top Cone Typical Target Shape and Dimensions θt 200 mm θn side MD RCF θt top θn= 15 -135 mm θt= 75 - 440 mm HS RCF I=11019 W/cm2, E=19 J, Δτ=605 fs HD RCF MD RCF HS RCF LANEX HS RCF CR-39 Flat-top Cone Target Enhances Proton Beam Energy and Efficiency Flat-foil (slab) 15 mm x 2mm x 15 µm LA-UR-08-3173 K. A. Flippo, E. d'Humières, S. A. Gaillard, J. Rassuchine, et al. Phys. Plasmas 15, 056709 (2008)

  11. Ion Generation The laser-ion beam conversion efficiency is determined by the rates of loss mechanisms versus ion acceleration. • Efficiency enhanced by minimizing the target thickness • Thickness limited by breakout of shock from laser prepulse • Data from Key et al. (shown), Fuchs et al., IFSA 2005 • Efficiency enhanced by increasing mass ratio of matrix / accelerated ions (minimize loss to matrix ions) • Efficiency enhanced by minimizing collisional losses • Work is needed to understand design tradeoffs.

  12. Theory • Recent theoretical insights: • Two beam, shaped ignition at only 6-7 kJ compatible with HIPER (Temporal, Atzeni, Honrubia, POP 2008) • BOA, RPD mechanism predicted • Improved simulation capabilities lead to better understanding of the acceleration mechanism • Code predictions to be experimentally tested

  13. 20 µm neck Bottom Line: ~63% absorption~14 MeV 10 µm neck (shown) Bottom Line: ~78% absorption~26 MeV“Best Case” On axis (previous best case) 90 µm top (shown) Bottom Line: “Best Case”~78% absorption~26 MeV Bottom Line: “Best Case”~78% absorption~26 MeV 18 µm off-axis (shown) Bottom Line: White arrow shows approximate entrance offset of laser beam. Red arrow indicates where the electric field is highest (also in previous best case) Absorption down and proton energy down to flat-foil levels 20 µm top Bottom Line: Absorption up slightly, andproton energydown slightly Simulations Show Geometry and Plasma Conditions Affect the Sheath formation and Proton Energy but Electron Temperature Remains About the Same 1-µm scale-lengthpreplasma (shown) Bottom Line: “Best Case”~78% absorption~26 MeV 2nc preplasma Bottom Line: Absorption up butproton energydown to ~18 MeV Simulations by Emmanuel d'Humières, UNR currently at CHPT Ecole Polytechnique

  14. 6 MeV 10 MeV 15 MeV Expansion modeling and PIC-simulations 2/2 • Construct transfer function, that maps positions of proton to their respective momenta • Solve equations of motion of proton flow • Charged Particle Transfer (CPT) Codeby H. Ruhl, M. Schollmeier • Trident shot #18500 • top left: experiment RCF • CPT fitted to experiment • - top right: RCF image • - bottom left: envelope • - bottom right: transverse emittance

  15. C-based The laser-breakout afterburner*: a path to high efficiency & high energy ion beam. • Requirements: • Ultra-high laser contrast, ~ 1021 W/cm2 • Ultra-thin targets (e.g., ~ 30 nm C) • 1D & 2D Simulations using VPIC code • Start with solid density C, including cases with H contaminants • Mechanism: • Laser penetration across target • Electron heating • Electron energy  ion energy via kinetic Buneman instability. • Initial Results: • 35% (1D, 15% in 2D) of all ions accelerated to 0.3 GeV  7%, 4% conversion efficiency. • C-ion acceleration is immune to surface proton contamination! This concept is the new focus of LANL research in ion-beam generation Simulations by Brian Albright X-1-PTA LANL * Yin et al., Laser and Part. Beams 24, P. 291 (2006); Phys. Plasmas 14, 056706 (2007)

  16. 3D VPIC simulation of the RPA mechanism has beenperformed to examine higher-dimensional effects • Our largest simulation to date on ion acceleration (run on Roadrunner base system): • Physical domain 25x25x20 μm w/ solid target density 14x109 cells, 21 x 109 particles, • 4096 processors • Contrasting with sim. size at the time of the proposal: • 0.5x109 cells, 2.2x109 particles, 510 processors • 3D visualization using EnSight server-of-servers mode enables viewing, analysis of very large (multiple-TB) data sets. Circular polarization, 30nm C and I0=1021 W/cm2 & 312 fs pulse Simulations by Lin Yin X-1-PTA LANL

  17. LASNEX Simulation Shows Two Carbon Beams (480 MeV) with 7.2 kJ Yields a Gain of 6.5 35.5 kJ absorbed laser energy, peak fuel density is ρDT ~ 150 g/cc. 14.2 ns pulse (foot + P~ t3.5 pulse) that peaks at 270 eV, Simulations by Brian Albright X-1-PTA LANL

  18. Questions • 10 ps ion acceleration and instabilities of the laser in preplasma • overlap of multiple beams • source stability, ion depletion • conversion efficiency • higher Z ions (still Maxwellian) • stopping in degenerate plasma

  19. T7 T8 T6 T5 T3 T4 T2 T1 t8 t1 t2 t3 t5 t6 t7 t4 Proton Fast ignition - target stability (1) Target under consideration: 1-D 3-T code DEIRA High yield target: 4.4 mg fuel mass, yield 500 MJ 2.7 mm Be 2.5 mm DT ice 2.25 mm Driving X-ray pulse: DT gas t1 = 2.0 ns, T1 = 90 eV; t2 = 24.0 ns, T2 = 95 eV; t3 = 26.0 ns, T3 = 110 eV; t4 = 32.0 ns, T4 = 110 eV; t5 = 34.5 ns, T5 = 130 eV; t6 = 39.0 ns, T6 = 145 eV; t7 = 44.0 ns, T7 = 240 eV; t8 = 46.0 ns, T8 = 240 eV; Tx Driving pulse for optimum compression without ignition Absorbed X-ray energy: Ecaps 1 MJ; Implosion velocity: vim = 2.40107 cm/s; Maximum compression: rm = 3.53 g/cm2 at tm = 47.76 ns, RDT = 0.180 mm, rDT = 180 – 260 g/cm3, TDT = 0.80 – 0.38 keV;

  20. Proton fast ignition - target stability (2) Problems: 1) Proton production target rear surface has to remain cold 2) A vacuum gap for acceleration is required 3) distance between proton target and capsule should be small Proton target is closely attached to the target or hohlraum therefore subject to the soft-x-rays driving the capsule A shield is required to protect the production target Requirements for the shield: as thin as possible to avoid energy loss/straggling thick enough to protect the target

  21. Proton fast ignition - target stability (3)

  22. Proton fast ignition - target stability (4)

  23. Proton fast ignition - target stability (5) Conclusion: a 50 µm shield is displaced by 280 µm at the time of ignition (maximum compression) the shield is heated up to 2-3 eV at the time of ignition temperature of the production target closely coupled to the shield (a problem ? Evaporation of proton layers) a second (thin) shield could further reduce the thermal load on the target

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