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Lecture 2: Symmetry issues Oswald Willi Institut für Laser- und Plasmaphysik Vorlesung SS 2007 User ID: Laser Passwort: Plasma Tel. 0211 81 12157

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Presentation on theme: "Lecture 2: Symmetry issues Oswald Willi Institut für Laser- und Plasmaphysik Vorlesung SS 2007 User ID: Laser Passwort: Plasma Tel. 0211 81 12157"— Presentation transcript:

1 Lecture 2: Symmetry issues Oswald Willi Institut für Laser- und Plasmaphysik Vorlesung SS 2007 User ID: Laser Passwort: Plasma Tel

2 Different ignition concepts

3 The Rayleigh-Taylor instability RT instability in inertial confinement fusion RT instability induced by laser imprint RT instability induced by target modulations

4 The Rayleigh-Taylor instability occurs when a heavy fluid sits on top of a lighter fluid

5 The RT instability is studied due to its potential to degrade the implosion performance

6 Rayleigh-Taylor instability

7 Face on and side on radiographic techniques are used to measure RT growth

8 Temporal evolution of the Rayleigh-Taylor instability (Osaka)

9 A shaped, low adiabat x-ray drive is generated in a hohlraum. Foil diagnosis is through imaging in back illumination with x-rays.

10 Rayleigh-Taylor instability

11 Ablative stabilization reduces the growth rate, results from material flowing through the RT unstable region with a velocity v a

12 RT growth rate scaling with wavelength

13 For ICF, a high aspect ratio target is required to amplify the ablation pressure, but Rayleigh-Taylor instability limits the aspect ratio

14 Cylindrical Rayleigh-Taylor instability

15 A series of 2-D images showing RT growth in converging geometry

16 3-D hydrodynamic simulations of RT instability at fuel-pusher interface

17 The uniformity problem

18 Laser imprinting and the RT instability in inertial confinement fusion

19 The physical process of imprint is similar to that of the classical Richtmyer - Meshkov instability

20 Laser spatial non-uniformities give rise to perturbations in the driving pressure

21 Mechanism for non-uniform imprinting due to lack of thermal smoothing

22 Observations of laser imprinting and 3-D hydro- code simulations

23 Considerable growth is observed in the case of a smooth CH foil driven by a laser beam with a single 60µm mode perturbation

24 Model based on single-mode imprint scalings from simulations predicts multi-mode result

25 Single-mode imprint simulations provide scalings for time and amplitude of saturation

26 Saturation of imprint is predicted by single mode simulations for start-up conditions

27 Proposed solutions to the imprint problem Multi-wavelength drive Problem: early-time imprint is still a problem, even at long Low intensity start-up Problem: imprint still seen at the very lowest irradiances Ultra-broad bandwidth lasers Problem: not developed Beam smoothing techniques Problem: expensive Indirect-direct drive Foam.buffered targets Indirect drive Problem: unable to control the blow-off plasma, leading to large instability generation. Also - strong shock wave launched into the solid - preheat Supersonic x-ray preheating of a foam overcoat. Large initial D ac can be created, with no blow-off problem and shock generation Problem: conversation to x-rays

28 Schematic of the operation of random phase plate arrays

29 Random phase plates and equivalent focal planes

30 Arrangement of induced spatial incoherence system

31 Variation of ISI smoothing with bandwidth

32 Even ISI irradiation still show plasma non- uniformities

33 Equivalent plane images of raw and optically smoothed laser beams

34 Side-on XUV radiographs of premodulated CH foils driven by coherent, ISI/RPP smoothed laser drives and soft x-rays to bare targets

35 Plasma smoothing

36 Thermal smoothing of non-uniform laser deposition in a preformed plasma

37 Schematic of hybrid x-ray optical drive schemes using foam overcoats

38 Diffusive electron conduction acts to thermally smooth the non-uniform energy deposition fusion

39 Soft x-ray imaging system with submicron spatial resolution

40 Transmission radiograph recorded on a foil target irradiated by an RPP-smoothed laser

41 Transmission radiograph recorded on an uncoated foam + foil target

42 Foam buffering mitigates the imprint problem

43 2D LASNEX simulations show the increased scalelength in the gold-coated foam target

44 Density contour plots of a plain plastic foil accelerated with coherent radiation

45 Density contour plots of a CH foil and pre-irradiated foam buffer layer accelerated with coherent radiation

46 Simulation of laser imprint seeding and RT growth

47 Foam overcoatings have been shown to affect imprinting and target stability

48 Spitzer simulations of foam-buffered targets show higher ablation velocities and reduced RT growth compared to bare targets


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