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ABSTRACT: The energy in hot electrons produced by the two plasmon decay instability, in planar targets, is measured to be the same when driven by one or two laser beams and significantly reduced with four for a constant overlapped intensity on the OMEGA EP. This is caused by multiple beams sharing the same common electron-plasma wave. A model, consistent with the experimental results, predicts that multiple laser beams can only drive a resonant common two plasmon decay electron-plasma wave in the region of wave numbers bisecting the beams. In this region, the gain is proportional to the overlapped laser beam intensity.
Physical Review Letters 10/2012; 109(15):155007. · 7.37 Impact Factor
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ABSTRACT: High resolution measurements of N2 and O2 broadening and shift coefficients for more than 100 H2O absorption lines have been performed. Data on the broadening and shift coefficients were obtained from the analysis of the
absorption spectra, recorded in the 8650–9020 cm−1 spectral region at room temperature with the help of an IFS 125 HR Fourier spectrometer at a spectral resolution of 0.01
cm−1. It is shown that for a more exact definition of the line shift coefficients, it is necessary to take into account the contribution
of all neighboring lines, even with an intensity two orders of magnitude lower than that of the measured line. A linear pressure
dependence of line shifts was observed for all of the buffer gases.
Atmospheric and Oceanic Optics 04/2012; 23(6):455-461.
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[show abstract]
[hide abstract]
ABSTRACT: The combination vibrational bands ν5 + ν9 and ν1 + ν11 of ethylene absorption adsorbed by silica aerogel nanopores of different densities have been studied for the first time in
the 5700- to 6300-cm−1 spectral region. The conducted measurements show significant differences between the spectra of ethylene in aerogels and
ethylene in the gas phase, which consist of the change of the absorption band shapes, the shift of the band frequency, and
the increase of the absorption intensity. It was concluded that in the studied pressure range of 88–952 mbar, the adsorbed
ethylene is in the same structural state.
Atmospheric and Oceanic Optics 04/2012; 23(4):266-269.
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P M Nilson,
J R Davies,
W Theobald,
P A Jaanimagi,
C Mileham,
R K Jungquist,
C Stoeckl,
I A Begishev, A A Solodov,
J F Myatt,
J D Zuegel,
T C Sangster,
R Betti,
D D Meyerhofer
[show abstract]
[hide abstract]
ABSTRACT: Time-resolved K(α) spectroscopy has been used to infer the hot-electron equilibration dynamics in high-intensity laser interactions with picosecond pulses and thin-foil solid targets. The measured K(α)-emission pulse width increases from ~3 to 6 ps for laser intensities from ~10(18) to 10(19) W/cm(2). Collisional energy-transfer model calculations suggest that hot electrons with mean energies from ~0.8 to 2 MeV are contained inside the target. The inferred mean hot-electron energies are broadly consistent with ponderomotive scaling over the relevant intensity range.
Physical Review Letters 02/2012; 108(8):085002. · 7.37 Impact Factor
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D H Froula,
D T Michel,
I V Igumenshchev,
S X Hu,
B Yaakobi,
J F Myatt,
D H Edgell,
R Follett,
V Y Glebov,
V N Goncharov,
T J Kessler,
A V Maximov,
P B Radha,
T C Sangster,
W Seka,
R W Short, A A Solodov,
C Sorce,
C Stoeckl
[show abstract]
[hide abstract]
ABSTRACT: Direct-drive ignition is most susceptible to multiple-beam laser-plasma instabilities, as the single-beam intensities are low (I-s similar to 10(14)W cm(-2)) and the electron temperature in the underdense plasma is high (T-e similar or equal to 3.5 keV). Cross-beam energy transfer is driven by multiple laser beams and can significantly reduce the hydrodynamic efficiency in direct-drive experiments on OMEGA (Boehly et al 1997 Opt. Commun. 133 495). Reducing the radii of the laser beams significantly increases the hydrodynamic efficiency at the cost of an increase in the low-mode modulations. Initial 2D hydrodynamic simulations indicate that zooming, transitioning the laser-beam radius prior to the main drive, does not increase low-mode nonuniformities. The combination of zooming and dynamic bandwidth reduction will provide a 30% effective increase in the drive energy on OMEGA direct-drive implosions. It was shown that two-plasmon decay (TPD) can be driven by multiple laser beams and both planar and spherical experiments were performed to study the hot electrons generated by TPD. The fraction of laser energy converted to hot electrons scales with the hot-electron temperature for all geometries and over a wide range of intensities. At ignition-relevant intensities, the fraction of laser energy converted to hot electrons is measured to decrease by an order of magnitude when the ablator material is changed from carbon-hydrogen to aluminum. The TPD results are compared with a multiple-beam linear theory and a nonlinear Zakharov model.
Plasma Physics and Controlled Fusion 01/2012; 54(12). · 2.42 Impact Factor
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W. Theobald, A. A. Solodov,
C. Stoeckl,
K. S. Anderson,
R. Betti,
T. R. Boehly,
R. S. Craxton,
J. A. Delettrez,
C. Dorrer,
J. A. Frenje, [......],
P. M. Nilson,
P. K. Patel,
H. Chen,
T. C. Sangster,
W. Seka,
N. Sinenian,
T. Ma,
F. N. Beg,
E. Giraldez,
R. B. Stephens
[show abstract]
[hide abstract]
ABSTRACT: Fast ignition is a two-step inertial confinement fusion concept where megaelectron volt electrons ignite the compressed core of an imploded fuel capsule driven by a relatively low-implosion velocity. Initial surrogate cone-in-shell, fast-ignitor experiments using a highly shaped driver pulse to assemble a dense core in front of the cone tip were performed on the OMEGA/OMEGA EP Laser [
T. R. Boehly et al., Opt. Commun. 133, 495 (1997)
;
L. J. Waxer et al., Opt. Photonics News 16, 30 (2005)
]. With optimal timing, the OMEGA EP pulse produced up to ∼1.4 × 107 additional neutrons which is a factor of ∼4 more neutrons than without short-pulse heating. Shock-breakout measurements performed with the same targets and drive conditions demonstrate an intact cone tip at the time when the additional neutrons are produced. Velocity interferometer system for any reflector measurements show that x-rays from the shell’s coronal plasma preheat the inner cone wall of thin-walled Au cones, while the thick-walled cones that are used in the integrated experiments are not affected by preheat.
Physics of Plasmas 05/2011; 18(5):056305-056305-11. · 2.15 Impact Factor
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P.B. Radha,
R. Betti,
T.R. Boehly,
J.A. Delettrez,
D.H. Edgell,
V.N. Goncharov,
I.V. Igumenshchev,
J.P. Knauer,
J.A. Marozas,
F.J. Marshall, [......],
T.C. Sangster,
W. Seka,
S. Skupsky, A.A. Solodov,
C. Stoeckl,
W. Theobald,
J.A. Frenje,
D.T. Casey,
C.K. Li,
R.D. Petrasso
[show abstract]
[hide abstract]
ABSTRACT: The OMEGA laser system is being used to investigate several approaches to inertial confinement fusion: the traditional central-hot-spot (CHS) ignition, fast ignition (FI), and shock ignition (SI). To achieve ignition, CHS requires the highly uniform compression of a solid deuterium-tritium (DT)-layered target on a low adiabat (defined as the ratio of the pressure to the Fermi-degenerate pressure) and with an implosion velocity V <sub>imp</sub> ≥ 3.5 × 10<sup>7</sup> cm/s. A laser pulse shape with triple pickets is used to produce this low adiabat by optimally timing multiple shocks launched by the pickets and the main laser. Cryogenic targets that imploded optimally with such pulses have demonstrated near-design compression with an areal density ρ R ~ 290 mg/cm<sup>2</sup> at V <sub>imp</sub> = 3.1 × 10<sup>7</sup> cm/s. These are, by far, the highest DT areal densities demonstrated in the laboratory. SI experiments, where a shock is launched by a picket at the end of the laser pulse into the compressing capsule, have been performed on low-adiabat warm plastic targets. Both yield and areal density improve significantly when a spike is used at the end of the laser pulse, indicating that the energy from the shock is coupled into the compressing target. Integrated FI experiments have begun on the OMEGA/OMEGA EP laser system.
IEEE Transactions on Plasma Science 05/2011; · 1.17 Impact Factor
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P. M. Nilson, A. A. Solodov,
J. F. Myatt,
W. Theobald,
P. A. Jaanimagi,
L. Gao,
C. Stoeckl,
R. S. Craxton,
J. A. Delettrez,
B. Yaakobi,
J. D. Zuegel,
B. E. Kruschwitz,
C. Dorrer,
J. H. Kelly,
K. U. Akli,
P. K. Patel,
A. J. Mackinnon,
R. Betti,
T. C. Sangster,
D. D. Meyerhofer
[show abstract]
[hide abstract]
ABSTRACT: Experiments have been performed to determine the effect of laser-pulse duration and energy on hot-electron–generation efficiency at high intensity. Thin copper foil targets were irradiated with 1 to 2100 J, 1 to 10 ps pulses focused to intensities >1018 W/cm2. The target volume was varied from 75 × 75 × 3 μm3 to 600 × 600 × 50 μm3 to access a range of bulk thermal-electron temperatures up to several hundred electron volts. Comparison of K-photon spectroscopy measurements from these targets with electron transport and radiation-generation calculations indicates that the energy conversion efficiency into hot electrons is 20 ± 10%, independent of laser-pulse duration and energy.
Physics of Plasmas 04/2011; 18(5):056703-056703-6. · 2.15 Impact Factor
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ABSTRACT: The absorption spectrum of the water vapor, confined in the nanoporous silica aerogel, was measured within 5000-5600 cm(-1) with the IFS 125 HR Fourier spectrometer. It has been shown, that tight confinement of the molecules by the nanoporous size leads to the strong lines broadening and shift. For water vapor lines, the HWHM of confined molecules are on the average 23 times larger than those for free molecules. The shift values are in the range from -0.03 cm(-1) to 0.09 cm(-1). Some spectral lines have negative shift. The data on the half-widths and center shifts for some strongest H(2)O lines have been presented.
Optics Express 12/2010; 18(25):26062-7. · 3.59 Impact Factor
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P M Nilson, A A Solodov,
J F Myatt,
W Theobald,
P A Jaanimagi,
L Gao,
C Stoeckl,
R S Craxton,
J A Delettrez,
B Yaakobi,
J D Zuegel,
B E Kruschwitz,
C Dorrer,
J H Kelly,
K U Akli,
P K Patel,
A J Mackinnon,
R Betti,
T C Sangster,
D D Meyerhofer
[show abstract]
[hide abstract]
ABSTRACT: Thin-foil targets were irradiated with high-power (1 ≤ P(L) ≤ 210 TW), 10-ps pulses focused to intensities of I>10(18) W/cm(2) and studied with K-photon spectroscopy. Comparing the energy emitted in K photons to target-heating calculations shows a laser-energy-coupling efficiency to hot electrons of η(L-e) = 20 ± 10%. Time-resolved x-ray emission measurements suggest that laser energy is coupled to hot electrons over the entire duration of the incident laser drive. Comparison of the K-photon emission data to previous data at similar laser intensities shows that η(L-e) is independent of laser-pulse duration from 1 ≤ τ(p) ≤ 10 ps.
Physical Review Letters 12/2010; 105(23):235001. · 7.37 Impact Factor
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[show abstract]
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ABSTRACT: Three-dimensional simulations of solid-target electron-transport experiments have been performed, using the hybrid-PIC code LSP. The experimentally observed fast-electron divergence half-angle of 16° in the target was reproduced assuming an initial divergence half-angle of ~56°, close to the value expected from the simple ponderomotive acceleration formula: where γ is the electron relativistic factor. The simulations accurately reproduce the details of the electron transport observed in the experiment. The electron beam propagates as an expanding annulus that breaks into filaments due to the resistive filamentation instability. The electron-beam partial collimation and annular propagation is due to the resistive azimuthal magnetic field generated at the outer edge of the electron beam.
Journal of Physics Conference Series 09/2010; 244(2):022063.
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W Theobald,
K S Anderson,
R Betti,
R S Craxton,
J A Delettrez,
J A Frenje,
V Yu Glebov,
O V Gotchev,
J H Kelly,
C K Li, [......],
R D Petrasso,
P B Radha,
C Ren,
T C Sangster,
W Seka,
V A Smalyuk, A A Solodov,
R B Stephens,
C Stoeckl,
B Yaakobi
[show abstract]
[hide abstract]
ABSTRACT: Advanced ignition concepts, such as fast ignition and shock ignition, are being investigated at the Omega Laser Facility. Integrated fast-ignition experiments with room-temperature re-entrant cone targets have begun, using 18 kJ of 351 nm drive energy to implode empty 40 µm thick CD shells, followed by 1.0 kJ of 1053 nm wavelength, short-pulse energy. Short pulses of 10 ps width have irradiated the inside of a hollow gold re-entrant cone at the time of peak compression. A threefold increase in the time-integrated, 2 to 7 keV x-ray emission was observed with x-ray pinhole cameras, indicating that energy is coupled from the short-pulse laser into the core by fast electrons. In shock-ignition experiments, spherical plastic-shell targets were compressed to high areal densities on a low adiabat, and a strong shock wave was sent into the converging, compressed capsule. In one experiment, 60 beams were used with an intensity spike at the end of the laser pulse, and the implosion performance was studied through neutron-yield and areal-density measurements. In a second experiment, the 60 OMEGA beams were split into a 40+20 configuration, with 40 low-intensity beams used for fuel assembly and 20 delayed beams with a short, high-intensity pulse shape (up to 1 × 1016 W cm−2) for shock generation.
Plasma Physics and Controlled Fusion 11/2009; 51(12):124052. · 2.42 Impact Factor
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M Storm, A A Solodov,
J F Myatt,
D D Meyerhofer,
C Stoeckl,
C Mileham,
R Betti,
P M Nilson,
T C Sangster,
W Theobald,
Chunlei Guo
[show abstract]
[hide abstract]
ABSTRACT: High-resolution coherent transition radiation (CTR) imaging diagnoses electrons accelerated in laser-solid interactions with intensities of approximately 10;{19} W/cm;{2}. The CTR images indicate electron-beam filamentation and annular propagation. The beam temperature and half-angle divergence are inferred to be approximately 1.4 MeV and approximately 16 degrees , respectively. Three-dimensional hybrid-particle-in-cell code simulations reproduce the details of the CTR images assuming an initial half-angle divergence of approximately 56 degrees . Self-generated resistive magnetic fields are responsible for the difference between the initial and measured divergence.
Physical Review Letters 07/2009; 102(23):235004. · 7.37 Impact Factor
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ABSTRACT: A thorough understanding of future integrated fast-ignition experiments combining compression and heating of high-density thermonuclear fuel requires hybrid (fluid+particle) simulations of the implosion and ignition process. Different spatial and temporal scales need to be resolved to model the entire fast-ignition experiment. The two-dimensional (2D) axisymmetric hydrocode DRACO [
P. B. Radha et al., Phys. Plasmas 12, 056307 (2005)
] and the 2D/three-dimensional hybrid particle-in-cell code LSP [
D. R. Welch et al., Nucl. Instrum. Methods Phys. Res. A 464, 134 (2001)
] have been integrated to simulate the implosion and heating of direct-drive, fast-ignition fusion targets. DRACO includes the physics required to simulate compression, ignition, and burn of fast-ignition targets. LSP simulates the transport of hot electrons from the place where they are generated to the dense fuel core where their energy is absorbed. The results from integrated simulations of cone-in-shell CD targets designed for fast-ignition experiments on OMEGA [
T. R. Boehly et al., Opt. Commun. 133, 495 (1997)
;
C. Stoeckl et al., Fusion Sci. Technol. 49, 367 (2006)
] are presented. Target heating and neutron yields are computed. The results from LSP simulations of electron transport in solid-density plastic targets are also presented. They confirm an increase in the electron divergence angle with the laser intensity in the current experiments. The self-generated resistive magnetic field is found to collimate the hot-electron beam and increase the coupling efficiency of hot electrons with the target. Resistive filamentation of the hot-electron beam is also observed.
Physics of Plasmas 04/2009; 16(5):056309-056309-9. · 2.15 Impact Factor
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[show abstract]
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ABSTRACT: The performance of high-gain, fast-ignition fusion targets is investigated using one-dimensional hydrodynamic simulations of implosion and two-dimensional (2D) hybrid fluid-particle simulations of hot-electron transport, ignition, and burn. The 2D/3D hybrid-particle-in-cell code LSP [
D. R. Welch et al., Nucl. Instrum. Methods Phys. Res. A 464, 134 (2001)
] and the 2D fluid code DRACO [
P. B. Radha et al., Phys. Plasmas 12, 056307 (2005)
] are integrated to simulate the hot-electron transport and heating for direct-drive fast-ignition targets. LSP simulates the transport of hot electrons from the place where they are generated to the dense fuel core where their energy is absorbed. DRACO includes the physics required to simulate compression, ignition, and burn of fast-ignition targets. The self-generated resistive magnetic field is found to collimate the hot-electron beam, increase the coupling efficiency of hot electrons with the target, and reduce the minimum energy required for ignition. Resistive filamentation of the hot-electron beam is also observed. The minimum energy required for ignition is found for hot electrons with realistic angular spread and Maxwellian energy-distribution function.
Physics of Plasmas 11/2008; 15(11):112702-112702-6. · 2.15 Impact Factor
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C Stoeckl,
K S Anderson,
R Betti,
T R Boehly,
J A Delettrez,
J A Frenje,
V N Goncharov,
V Yu Glebov,
J H Kelly,
A J MacKinnon, [......],
P M Nilson,
R D Petrasso,
T C Sangster, A A Solodov,
R B Stephens,
M Storm,
W Theobald,
B Yaakobi,
L J Waxer,
C D Zhou
[show abstract]
[hide abstract]
ABSTRACT: A comprehensive scientific program is being pursued at LLE to explore the physics of fast ignition. The OMEGA EP Laser was completed in April 2008, adjacent to the 60 beam, 30 kJ OMEGA Laser Facility. OMEGA EP consists of four beamlines with a NIF-like architecture, each delivering up to 6.5 kJ of UV laser energy in long pulse (ns) mode into the OMEGA EP target chamber. Two of the beamlines can operate as high-energy petawatt lasers, with up to 2.6 kJ each with 10 ps pulse duration. These beams can either be injected into the OMEGA EP target chamber or combined collinearly into the existing OMEGA target chamber for integrated fast-ignitor experiments. Fuel-assembly experiments on OMEGA have achieved high fuel areal densities, and the effects of a cone on the fuel assembly are being studied. Experiments on short-pulse laser systems in collaboration with other institutions are being pursued to investigate the conversion efficiency from laser energy to fast electrons. A coherent transition radiation diagnostic to study the transport of the electrons in high-density material is being developed. Integrated experiments with room-temperature targets on OMEGA will be performed in 2008. Simulations of these integrated experiments show significant heating of up to 1 keV due to the hot electrons from the short-pulse laser.
Plasma Physics and Controlled Fusion 11/2008; 50(12):124044. · 2.42 Impact Factor
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[show abstract]
[hide abstract]
ABSTRACT: Current theoretical predictions of the stopping range of fast electrons in the dense cores of fast-ignition fusion targets differ by about a factor of 2. Inconsistencies in the previous derivations are discussed and correct values of the stopping power, scattering coefficients, and ranges of fast electrons are obtained. Such more-accurate results can be used in theoretical studies of the ignition conditions and particles-in-cell and Monte Carlo simulations of the collisional electron transport in the plasma of fast-ignition targets. Convenient approximate relations for the stopping range and angular moments of the hot-electron distribution function are also obtained.
Physics of Plasmas 04/2008; 15(4):042707-042707-5. · 2.15 Impact Factor
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W. Theobald,
R. Betti,
C. Stoeckl,
K. S. Anderson,
J. A. Delettrez,
V. Yu. Glebov,
V. N. Goncharov,
F. J. Marshall,
D. N. Maywar,
R. L. McCrory, [......],
D. Shvarts,
V. A. Smalyuk, A. A. Solodov,
B. Yaakobi,
C. D. Zhou,
J. A. Frenje,
C. K. Li,
F. H. Séguin,
R. D. Petrasso,
L. J. Perkins
[show abstract]
[hide abstract]
ABSTRACT: Shock ignition is a two-step inertial confinement fusion concept where a strong shock wave is launched at the end of the laser pulse to ignite the compressed core of a low-velocity implosion. Initial shock-ignition technique experiments were performed at the OMEGA Laser Facility [
T. R. Boehly et al., Opt. Commun. 133, 495 (1997)
] using 40-μm-thick, 0.9-mm-diam, warm surrogate plastic shells filled with deuterium gas. The experiments showed a significant improvement in the performance of low-adiabat, low-velocity implosions compared to conventional “hot-spot” implosions. High areal densities with average values exceeding ∼ 0.2 g/cm2 and peak areal densities above 0.3 g/cm2 were measured, which is in good agreement with one-dimensional hydrodynamical simulation predictions. Shock-ignition technique implosions with cryogenic deuterium and deuterium-tritium ice shells produced areal densities close to the 1D prediction and achieved up to 12% of the predicted 1D fusion yield.
Physics of Plasmas 03/2008; 15(5):056306-056306-9. · 2.15 Impact Factor
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[show abstract]
[hide abstract]
ABSTRACT: Hydrodynamic simulations of realistic high-gain fast-ignition targets are performed, including one-dimensional simulations of the implosion and two-dimensional simulations of ignition by a collimated electron beam and burn propagation. These simulations are used to generate gain curves for fast-ignition direct-drive inertial confinement fusion. The minimum energy required for ignition is computed for fast-electron beams with a monoenergetic or Maxwellian distribution, generated by a constant or Gaussian laser pulse. It is found that realistic fast-ignition targets can be ignited by monoenergetic collimated electron beams with a radius of 20 μm, duration of 10 ps, and energy of 15 kJ. Simulations using ponderomotive temperature scaling for fast electrons and Gaussian laser pulses predict a minimum laser energy for ignition of 235 kJ (105 kJ) for the energy conversion efficiency from the laser to fast electrons 0.3 (0.5) and the wavelength of 1.054 μm. Such large energies are required because ultra-intense lasers are predicted to generate very energetic (multi-MeV) electrons with stopping distance exceeding the target size. The fast-electron energy, the stopping distance and the minimum energy required for ignition can be reduced using frequency-doubled laser pulses. Simulations of idealized cone targets are also performed in order to determine a lower bound of the gain deterioration due to the cone.
Physics of Plasmas 06/2007; 14(6):062701-062701-11. · 2.15 Impact Factor
