Critical Path to Impact Fast Ignition Suppression of the Rayleigh-Taylor Instability

Transcription

1 Critical Path to Impact Fast Ignition Suppression of the Rayleigh-Taylor Instability H. Azechi Vice Director Institute of Laser Engineering, Osaka University Jpn-US WS on HIF and HEDP September 28, 2005 Utsunomiya Collaborators: Institute of Laser Engineering, Osaka University, M. Murakami,T. Sakaiya, S. Fujioka, H. Saito, H. Shiraga, M. Nakai, K. Shigemori, A. Sunahara, H. Nagatomo, Naval Research Laboratory, 1 SAIC Japan S. Obenschain, M. Karasik, J. Gardner, J. Bates, D. Colombant, J. Weaver, Y. Aglitskiy1,

2 Compression Fast Heating Ignition&Burn FIREX-I GEKKO-XII

3 Outline 1. Introduction to impact-fast-ignition 2. Suppression of the RT instability 3. First intened exp't 4. Future experiment

4 Sufficient suppression of the Rayleigh-Taylor instability 1. increases compressed density. 2. revives an old ignition idea: Super velocity (10 8 cm/s) implosion can configure a hot-spark without a main fuel so as to ignite at very low laser energy ( kj). This idea was rejected by two major criticisms: No pathway towards high gain. The Rayleigh-Taylor instability limits the maximum implosion velocity.

5 Pathway towards high gain Impact Fast Ignition Laser τ L O(nsec) Cone guide Ablator Impactproduced igniter DT layer 1) High gain Laser or X-ray radiation Compressed main DT fuel 2) Simple Physics 3) Low Cost Murakami, NIM-A '05

6 2D Hydrodynamic Simulation rho rho T T Isocontour map at a time shortly before the impact Isocontour map at peak compression shortly after the impact Ahigh-density spark plug is created by impact collision.

7 Suppression of RT is the critical issure. Double ablation (Fujioka, PRL04) Cocktailcolor (Ohtani, submitted) High-Z layer (NRL) Picket (Rochester, NRL)

8 RT instability in CHBr target Double Ablation When targets are doped with high-z material, xraysfromthehigh-zgenerateanewablationsurface. We considered the RT growth only at the radiative ablation front, because grad ρ grad p is almost positive, namely RT stable, at the electron-conduction ablation front. 1D simulation (ILESTA-1D) RT unstable region Density Pressure RT stable region Radiative ablation front S. Fujioka (ILE. Osaka) ILE OSAKA 2D simulation (RAICHO*) * N. Ohnishi et al., JQSRT 71, 551 (2001) Electron-conduction ablation front Density (g/cm 3 ) Radiation ele. Laser Pressure (Mbar) Position (µ X-ray-ablation Physical mechanism generally which stable makes because the electron-conduction of large mdot andablation L. Electron front to be ablation RT stable is stabilized is now under by large investigation. mdot upper stream and low ablation velocity.

9 RT exp t with perturbed CHBr target Growth of perturbations in a CHBr target is lower than that of the CH target. CHBr I L (TW/cm 2 ) 61 g (µm/ns 2 ) 42 L m (µm) 2.6 * R. Betti et al., PoP 5, 1446 (1998) ρ a (g/cm 3 ) 2.4 m (g/cm 2 s -1 ) 6.9 x 10 5 V a (µm/ns) 2.9 S. Fujioka (ILE. Osaka) Fr µm thickness CHBr λ p = 47 µm, a 0 = 0.3 µm 1 ns 20 CHBr Growth factor CH µm Time (ns)

10 RT exp. with shorter wavelength perturbation Growth of the perturbations in the CHBr target is strongly suppressed in comparison with that in the CH target. 18-µm thick CHBr λ p = 25 µm, a 0 = 0.3 µm 300 µm 25-µm thick CH λ p = 20 µm, a 0 = 0.2 µm 1 ns 1 ns Temporal evolution of growth factor CH Growth factor (arb. units) CHBr S. Fujioka (ILE. Osaka) 300 µm Time (ns) The theory predicts the RT growth rate to be 1.5 ns -1 in the CHBr target. This value is large enough to amplify the perturbation to be observable

11 Density profile Note: 1. Double ablation is clealy observed. 2. The target density is only slightly lowered. Peak density of the CHBr target is not lowered drastically in comparison with that of the CH target. S. Fujioka (ILE. Osaka) ns ns Density (g/cm 3 ) LASER Density (g/cm 3 ) LASER Experiment Simulation Position (µm) Position (µm) 80 Differences between the experimental result and the simulation may indicate a more detail atomic model is required for reproducing the full characteristics of the density profile in a CHBr

12 ν =0.5THz Completely independent 2D rad hydro-code has confirmed CHBr stability.

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15 Reduction of Rayleigh-Taylor Instability Growth with Multi-Color Laser Irr Growth factor Rayleigh-Taylor growth rate is reduced by two-color laser irradiation. Streaked image 1 ns 100 µm one-color Two-color (1/3+1/2-m ) : Single-color (λ= 1/3 µm) irradiation : Two-colors (λ= 1/3 and 1/2 µm) irradiation

16 Reduction of Rayleigh-Taylor Instability Growth with Multi-Color Laser Irr Multi-color irradiation sustains the peak de of the ablating target The density profile of laser-driven polystyrene 1/3 µm wavelength 1/3 µm and 1 µm wavelength single-color laser irradiationtwo-color laser irradiation t= 1.0 ns t= 1.3 ns Density (g/cm 3 ) Laser Density (g/cm 3 ) Laser Distance (µm) : Experimental Data : Fokker-Planck Simulation Distance (µm) : Experimental Data : Fokker-Planck Simulation

17 Experiments aiming at super velocity

18 HIPER-0.35µm and/or NIKE-0.25 µm are the facilities that can demonstrate super velocity. HIPER NIKE

19 HIPER Laser System High Intensity Plasma Experimental Research (HIPER) Target: CH, CHBr Focal length = 500 cm Effective F# = 3 KDP Main pulse Wavelength: 0.35 µm (3ω) Energy: 1.55 kj kj Intensity: ~ 4x10 14 W/cm 2 Beam smoothing: 2-D SS +KPP

20 Experimental procedure The target trajectory is measured by side-on backlightin Setup (top view) Laser BL target (Cu) ESM Basis (Be) Visible light measurem Shock & Temperature HIPER Laser Colliding foil (Cu) Slit: µm 12 Filter: Mg Plane target (CH, CHBr) X-ray Streak Camera ESM

21 2-3 x10 7 -cm/s velocity wasthelimitforgeneric CH targets irradiated by 1/2-µm laser. Self emission x-ray backlighting ~10-µm CH@~10 14 W/cm Self emission (#18957) BL image (#19078) 0 1 Time (ns) 100 m 0 1 Time (ns) 100 m Flying distance m) ( Foil disassembly is observed at late time Time (ns) 10 8 cm/s-velocity must be achieve, if RT-reduced targets 1/3-µm laser at higher irradiance.

22 1/3-µm laser irradiation: Highest velocity of 580 km/s has been demonstrated at CHBr target. x-ray backlighting #28864 CH 14 µm t #28865 CHBr 14 µm t Self emission #28872 CHBr 14 µm t 5 ns 5 ns 5 ns 200 µ m m 200 µ m m I L 2x10 14 W/cm m m I L 4x10 14 W/cm 2 Periodic intensity variation is due to diagnostics

23 CHBr trajectory indicates 580 km/s velocity with slightly lower acceleration than prediction. 400 Self emission #28872 CHBr 14 µm t 200 m m Flying distance µ m) ( ns Tim e (ns)

24 Future experiments

25 1. Inflight target density should be measured. #28895 CH 14 µm t + Cu 10 µm t ρ µm 2 ρ1d γ + 1 CH 14 µm t Cu 10 µm t 2 p 2 D V γ γ 1 ( γ + 1) p2 + 2ρ1D γ ( γ 1) p2 + 2ρ1D = 2 2 Time 2 t= Space (µm) col Target density is determined from D: shock velocity V: flyer velocity Test of diagnostics SHK28895_img indicates reasonablly good uniformity.

26 Second critical element Cone guide Ablator Impactproduced igniter Laser τ L O(nsec) DT layer Effective friction cone expansion dragging shell Laser or X-ray radiation Compressed main DT fuel Energy transmittance through a cone should be demonstrated.

27 With minor modification of FIREX-I, We may perform integrated experiment. FIREX-I GEKKO-XII

28 summary Suppression of the Rayleigh-Taylor instability is the key requirement for impact-fast-ignition (IFI). Super velocity of 1000 km/s is the critical path to IFI. 600 km/s velocity has been demonstrated at HIPER-0.35 µm experiments. In future: Density data and faster velocity will be taken in the coming Jan. exp't. Energytransmittance through a cone will also be measured. Integrated exp't can be performed with minor modification of FIREX-I laser.

29 New concepts have been generated every 10 years. 5. Early 00's: Impact ig.? 4. Mid 80's-90's: Fast ig. Hot-ele based ig. Central ig. 3. Late 70's: Hot spark ignition Volume ig. 2. Early 70's: Implosion 1. Early 60's: Birth of laser fusion