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1.
Phys Rev Lett ; 108(2): 025001, 2012 Jan 13.
Article in English | MEDLINE | ID: mdl-22324691

ABSTRACT

This Letter reports the first time-gated proton radiography of the spatial structure and temporal evolution of how the fill gas compresses the wall blowoff, inhibits plasma jet formation, and impedes plasma stagnation in the hohlraum interior. The potential roles of spontaneously generated electric and magnetic fields in the hohlraum dynamics and capsule implosion are discussed. It is shown that interpenetration of the two materials could result from the classical Rayleigh-Taylor instability occurring as the lighter, decelerating ionized fill gas pushes against the heavier, expanding gold wall blowoff. This experiment showed new observations of the effects of the fill gas on x-ray driven implosions, and an improved understanding of these results could impact the ongoing ignition experiments at the National Ignition Facility.

2.
Phys Rev E Stat Nonlin Soft Matter Phys ; 80(1 Pt 2): 016407, 2009 Jul.
Article in English | MEDLINE | ID: mdl-19658823

ABSTRACT

Recent experiments using proton backlighting of laser-foil interactions provide unique opportunities for studying magnetized plasma instabilities in laser-produced high-energy-density plasmas. Time-gated proton radiograph images indicate that the outer structure of a magnetic field entrained in a hemispherical plasma bubble becomes distinctly asymmetric after the laser turns off. It is shown that this asymmetry is a consequence of pressure-driven, resistive magnetohydrodynamic (MHD) interchange instabilities. In contrast to the predictions made by ideal MHD theory, the increasing plasma resistivity after laser turn-off allows for greater low-mode destabilization (m>1) from reduced stabilization by field-line bending. For laser-generated plasmas presented herein, a mode-number cutoff for stabilization of perturbations with m> approximately [8pibeta(1+D_{m}k_{ perpendicular};{2}gamma_{max};{-1})];{1/2} is found in the linear growth regime. The growth is measured and is found to be in reasonable agreement with model predictions.

3.
Phys Rev Lett ; 102(20): 205001, 2009 May 22.
Article in English | MEDLINE | ID: mdl-19519034

ABSTRACT

We report on the first proton radiography of laser-irradiated hohlraums. This experiment, with vacuum gold (Au) hohlraums, resulted in observations of self-generated magnetic fields with peak values approximately 10;{6} G. Time-gated radiographs of monoenergetic protons with discrete energies (15.0 and 3.3 MeV) reveal dynamic pictures of field structures and plasma flow. Near the end of the 1-ns laser drive, a stagnating Au plasma (approximately 10 mg cm;{-3}) forms at the center of the hohlraum. This is a consequence of supersonic, radially directed Au jets (approximately 1000 microm ns;{-1}, approximately Mach 4) that arise from the interaction of laser-driven plasma bubbles expanding into one another.

4.
Phys Rev Lett ; 100(18): 185006, 2008 May 09.
Article in English | MEDLINE | ID: mdl-18518386

ABSTRACT

The first observation of ignition-relevant areal-density deuterium from implosions of capsules with cryogenic fuel layers at ignition-relevant adiabats is reported. The experiments were performed on the 60-beam, 30-kJUV OMEGA Laser System [T. R. Boehly, Opt. Commun. 133, 495 (1997)10.1016/S0030-4018(96)00325-2]. Neutron-averaged areal densities of 202+/-7 mg/cm2 and 182+/-7 mg/cm2 (corresponding to estimated peak fuel densities in excess of 100 g/cm3) were inferred using an 18-kJ direct-drive pulse designed to put the converging fuel on an adiabat of 2.5. These areal densities are in good agreement with the predictions of hydrodynamic simulations indicating that the fuel adiabat can be accurately controlled under ignition-relevant conditions.

5.
Phys Rev Lett ; 92(20): 205001, 2004 May 21.
Article in English | MEDLINE | ID: mdl-15169359

ABSTRACT

Target areal density (rhoR) asymmetries in OMEGA direct-drive spherical implosions are studied. The rms variation / for low-mode-number structure is approximately proportional to the rms variation of on-target laser intensity / with an amplification factor of approximately 1/2(C(r)-1), where C(r) is the capsule convergence ratio. This result has critical implications for future work on the National Ignition Facility as well as OMEGA.

6.
Phys Rev Lett ; 92(18): 185002, 2004 May 07.
Article in English | MEDLINE | ID: mdl-15169493

ABSTRACT

The mixing of cold, high-density shell plasma with the low-density, hot spot plasma by the Rayleigh-Taylor instability in inertial confinement fusion is experimentally shown to correlate with the calculated perturbation feedthrough from the ablation surface to the inner shell surface. A fourfold decrease in the density of shell material in the mix region of direct drive implosions of gas filled spherical plastic shells having predicted convergence ratios approximately 15 was observed when laser imprint levels were reduced and the initial shell was thicker, corresponding to a reduction in the feedthrough rms level by a factor of 6. Shell mix is also shown to limit the spherical compression of the implosion.

7.
Phys Rev Lett ; 90(9): 095002, 2003 Mar 07.
Article in English | MEDLINE | ID: mdl-12689229

ABSTRACT

The areal density (rhoR) of D3He filled plastic capsules imploded at OMEGA has been measured at shock coalescence (1.7 ns) and, 400 ps later, during compressive burn, through the energy downshift of 14.7-MeV D3He protons. In this time interval, the azimuthally averaged rhoR changes from 13+/-2.5 to 70+/-8 mg/cm(2). The experiments demonstrate that fuel-shell mix is absent in the central regions at shock coalescence, and that the shell has no holes during compressive burn. We conjecture that rhoR asymmetries measured during compressive burn may be seeded by the time of shock coalescence.

8.
Phys Rev Lett ; 90(13): 135002, 2003 Apr 04.
Article in English | MEDLINE | ID: mdl-12689296

ABSTRACT

The temporal history of the target areal-density near peak compression of direct-drive spherical target implosions has been inferred with 14.7-MeV deuterium-helium-3 D3He proton spectroscopy of the 60-beam, 30-kJ UV OMEGA laser system. The target areal-density grows by a factor of approximately 8 during the time of neutron-production ( approximately 400 ps) before reaching 123+/-16 mg/cm(2) at peak compression in the implosion of a 950-micrometer-diam, 20-micrometer-thick plastic CH capsule filled with 4 atm of D3He fuel.

9.
Phys Rev Lett ; 89(16): 165002, 2002 Oct 14.
Article in English | MEDLINE | ID: mdl-12398729

ABSTRACT

Fuel-shell mix and implosion performance are studied for many capsule types in direct-drive experiments at OMEGA. The amount of mixing and the size of the mix region are inferred from charged-particle spectrometry data and confirmed with an experimentally constrained model. Measured yields and convergence ratios CR fall short of one-dimensional predictions, especially for low capsule fill pressures. CR is approximately 11 for pressures from 3 to 15 atm, in contrast to predictions of approximately 25 for 3 atm and approximately 12 for 15 atm. The performance shortfalls are likely to be caused by fuel-shell mix.

10.
Phys Rev Lett ; 89(8): 085003, 2002 Aug 19.
Article in English | MEDLINE | ID: mdl-12190476

ABSTRACT

The Rayleigh-Taylor instability in its highly nonlinear, turbulent stage causes atomic-scale mixing of the shell material with the fuel in the compressed core of inertial-confinement fusion targets. The density of shell material mixed into the outer core of direct-drive plastic-shell spherical-target implosions on the 60-beam, OMEGA laser system is estimated to be 3.4(+/-1.2) g/cm(3) from time-resolved x-ray spectroscopy, charged-particle spectroscopy, and core x-ray images. The estimated fuel density, 3.6(+/-1) g/cm(3), accounts for only approximately 50% of the neutron-burn-averaged electron density, n(e)=2.2(+/-0.4)x10(24) cm(-3).

12.
Appl Opt ; 12(5): 927-8, 1973 May 01.
Article in English | MEDLINE | ID: mdl-20125436
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