POP Nameplate
  • Volume/Page
  • Keyword
  • DOI
  • Citation
  • Advanced
   
 
 
 

Flickr Twitter iResearch App Facebook

Search Issue | RSS Feeds RSS
Previous Issue Next Issue

May 2001

Volume 8, Issue 5, pp. 1447-2594

Return to All Sections
back to top
RSS Feeds
back to top Inertially Confined Plasmas, Dense Plasmas, Equations of State

Stimulated Brillouin and Raman scattering from a randomized laser beam in large inhomogeneous collisional plasmas. II. Model description and comparison with experiments

V. T. Tikhonchuk, J. Fuchs, C. Labaune, S. Depierreux, S. Hüller, J. Myatt, and H. A. Baldis

Phys. Plasmas 8, 1636 (2001); http://dx.doi.org/10.1063/1.1357218 (14 pages) | Cited 18 times

Full Text: | Download PDF

Show Abstract
A model for stimulated Brillouin (SBS) and Raman (SRS) backscattering of a spatially smoothed laser beam interacting with a collisional, inhomogeneous, expanding plasma is presented. It is based on the independent hot spots description [H. A. Rose and D. F. DuBois, Phys. Rev. Lett. 72, 2883 (1994)], in which the overall plasma reflectivity is assumed to be a sum of the individual speckle reflectivities. Self-focusing is taken into account in the computation of the speckle intensity profile and reflectivities. Two additions have been made to previous similar theories: (i) the thermal effects are retained along with the ponderomotive force for what concerns speckle self-focusing, and (ii) SRS (convective and absolute) is accounted for in calculations of the speckle reflectivity. The model is benchmarked against recent laser–plasma experiments at Laboratoire pour l’Utilisation des Lasers Intenses, at École Polytechnique, France, with well-characterized interaction conditions. A good agreement is found between the experimental SBS levels and the model calculations using the measured plasma parameters. This agreement applies for two types of beam smoothing techniques, random phase plates, and polarization smoothing, various plasma densities, and laser energies. Self-focusing itself, and thermal effects in it, play both a fundamental role in defining the level of plasma backscattering. The absolute Raman instability in speckles dominates the SRS response. The model predictions for the SRS reflectivity are less satisfactory, although they demonstrate the same trends as the experimental data. It follows from model calculations and experimental data that the polarization smoothing technique provides an efficient method of control of parametric instabilities allowing a reduction of several times in the level of SBS and SRS reflectivities. © 2001 American Institute of Physics.
Show PACS
52.38.Bv Rayleigh scattering; stimulated Brillouin and Raman scattering
52.38.Hb Self-focussing, channeling, and filamentation in plasmas
52.38.Dx Laser light absorption in plasmas (collisional, parametric, etc.)
52.25.Os Emission, absorption, and scattering of electromagnetic radiation
52.35.Mw Nonlinear phenomena: waves, wave propagation, and other interactions (including parametric effects, mode coupling, ponderomotive effects, etc.)
52.35.Py Macroinstabilities (hydromagnetic, e.g., kink, fire-hose, mirror, ballooning, tearing, trapped-particle, flute, Rayleigh-Taylor, etc.)
52.25.-b Plasma properties
52.20.-j Elementary processes in plasmas

Electron kinetic simulations of solid density Al plasmas produced by intense subpicosecond laser pulses. I. Ionization dynamics in 30 femtosecond pulses

S. Ethier and J. P. Matte

Phys. Plasmas 8, 1650 (2001); http://dx.doi.org/10.1063/1.1357221 (9 pages) | Cited 10 times

Full Text: | Download PDF

Show Abstract
The interaction of a 1018 W/cm2, 30 fs laser pulse with solid Al was simulated with the electron kinetic code “FPI” [J. P. Matte et al., Phys. Rev. Lett. 72, 1208 (1994)] in which an improved average ion module was fully coupled to the electron kinetics. It includes electron impact ionization and excitation and their inverse processes: collisional recombination and de-excitation; as well as radiative decay and pressure ionization. We compare to runs without the inverse processes, and also without atomic physics (with 〈Z〉 set to 11). Atomic physics strongly affects the energy balance and the shape of the distribution function. Line radiation is mostly due to three body recombination into excited states after the peak of the pulse, as the plasma cools down. Despite the atomic processes and the high density, strongly non-Maxwellian distribution functions were obtained due to very steep temperature gradients and strong collisional heating, at the peak of the pulse. However, after the pulse, there is a very rapid thermalization of the electron distribution to which inverse processes strongly contribute. © 2001 American Institute of Physics.
Show PACS
52.25.Jm Ionization of plasmas
52.50.Jm Plasma production and heating by laser beams (laser-foil, laser-cluster, etc.)
52.25.Fi Transport properties
52.65.-y Plasma simulation

Formulation of radiation temperature in hohlraums with large radiation energy loss

Tieqiang Chang and Guangyu Wang

Phys. Plasmas 8, 1659 (2001); http://dx.doi.org/10.1063/1.1358891 (5 pages) | Cited 4 times

Full Text: | Download PDF

Show Abstract
This paper describes the radiation temperature of a hohlraum with large radiation energy loss. The hohlraum radiation temperature is crucial for indirect drive laser fusion and the radiation energy loss induced by the laser entrance hole or in other ways that can seriously reduce the radiation temperature. An analytic, concise formula is given in this paper, which needs not assume a special form of laser pulse. The corresponding numerical results are given for some typical laser pulses. It is shown that the temperature correction due to the radiation energy loss is sensitive to its area fraction, but relatively less sensitive to laser pulse shape, and weakly dependent of the incident laser energy. © 2001 American Institute of Physics.
Show PACS
52.50.Jm Plasma production and heating by laser beams (laser-foil, laser-cluster, etc.)
52.25.Os Emission, absorption, and scattering of electromagnetic radiation
44.40.+a Thermal radiation

Theory and simulation of electronic relativistic parametric instabilities for ultraintense laser pulses propagating in hot plasmas

A. Héron, J. C. Adam, G. Laval, and P. Mora

Phys. Plasmas 8, 1664 (2001); http://dx.doi.org/10.1063/1.1359744 (9 pages) | Cited 9 times

Full Text: | Download PDF

Show Abstract
The dispersion relation for electronic parametric instabilities of a circularly polarized laser wave is solved in the case where the distribution function is supposed to be cold in the transverse direction and to be a linear combination of a cold distribution function and of a Maxwellian in momentum in the longitudinal direction. Only densities below the critical density are considered. It is shown that the longitudinal temperature as expected reduces the growth rate, but that the existence of a hot tail is not sufficient to significantly reduce the instability. It is the bulk of the distribution function that must be heated to efficiently stabilize the system. Another important effect of the heating is to reduce the backscattered component of the instability. An example of a one-dimensional particle simulation performed in the exact conditions of validity of the theory is discussed. © 2001 American Institute of Physics.
Show PACS
52.35.Py Macroinstabilities (hydromagnetic, e.g., kink, fire-hose, mirror, ballooning, tearing, trapped-particle, flute, Rayleigh-Taylor, etc.)
52.27.Ny Relativistic plasmas
52.38.Dx Laser light absorption in plasmas (collisional, parametric, etc.)
52.65.Rr Particle-in-cell method
52.25.-b Plasma properties

Scaling and optimization of the radiation temperature in dynamic hohlraums

S. A. Slutz, M. R. Douglas, J. S. Lash, R. A. Vesey, G. A. Chandler, T. J. Nash, and M. S. Derzon

Phys. Plasmas 8, 1673 (2001); http://dx.doi.org/10.1063/1.1360213 (19 pages) | Cited 24 times

Full Text: | Download PDF

Show Abstract
A quasianalytic model of the dynamic hohlraum is presented. Results of the model are compared to both experiments and full numerical simulations with good agreement. The computational simplicity of the model allows one to find the behavior of the hohlraum radiation temperature as a function of the various parameters of the system and thus find optimum parameters as a function of the driving current. The model is used to investigate the benefits of ablative standoff and quasispherical Z pinches. © 2001 American Institute of Physics.
Show PACS
52.55.Ez Theta pinch
52.50.Lp Plasma production and heating by shock waves and compression
52.25.Os Emission, absorption, and scattering of electromagnetic radiation

Reduction of stimulated scattering losses from hohlraum plasmas with laser beam smoothing

S. H. Glenzer, R. L. Berger, L. M. Divol, R. K. Kirkwood, B. J. MacGowan, J. D. Moody, A. B. Langdon, L. J. Suter, and E. A. Williams

Phys. Plasmas 8, 1692 (2001); http://dx.doi.org/10.1063/1.1363613 (5 pages) | Cited 8 times

Full Text: | Download PDF

Show Abstract
Laser beam smoothing by spectral dispersion and by polarization smoothing has been observed to significantly reduce the scattering losses by stimulated Brillouin and stimulated Raman scattering from inertial confinement fusion hohlraums. For these measurements, the laser beam smoothing and the high-Z hohlraum wall plasma parameters approach the conditions of future inertial confinement fusion experiments. The simultaneous application of the smoothing techniques has reduced the scattering losses by almost one order of magnitude down to the 1% level. The experimental scaling of the stimulated Brillouin reflectivity compares well to modeling assuming nonlinear damping on the ion acoustic waves in three-dimensional nonlinear wave simulations and calculated hohlraum plasma conditions from radiation-hydrodynamic modeling. © 2001 American Institute of Physics.
Show PACS
52.57.-z Laser inertial confinement
52.38.Bv Rayleigh scattering; stimulated Brillouin and Raman scattering
52.35.Fp Electrostatic waves and oscillations (e.g., ion-acoustic waves)
52.35.Mw Nonlinear phenomena: waves, wave propagation, and other interactions (including parametric effects, mode coupling, ponderomotive effects, etc.)
52.25.Os Emission, absorption, and scattering of electromagnetic radiation
back to top
RSS Feeds

Shock timing technique for the National Ignition Facility

David H. Munro, Peter M. Celliers, Gilbert W. Collins, David M. Gold, Luiz B. Da Silva, Steven W. Haan, Robert C. Cauble, Bruce A. Hammel, and Warren W. Hsing

Phys. Plasmas 8, 2245 (2001); http://dx.doi.org/10.1063/1.1347037 (6 pages) | Cited 28 times

Full Text: | Download PDF

Show Abstract
Among the final shots at the Nova laser [Campbell et al., Rev. Sci. Instrum. 57, 2101 (1986)] was a series testing the VISAR (velocity interferometry system for any reflector) technique that will be the primary diagnostic for timing the shocks in a NIF (National Ignition Facility) ignition capsule. At Nova, the VISAR technique worked over the range of shock strengths and with the precision required for the NIF shock timing job—shock velocities in liquid D2 from 12 to 65 μm/ns with better than 2% accuracy. VISAR images showed stronger shocks overtaking weaker ones, which is the basis of the plan for setting the pulse shape for the NIF ignition campaign. The technique is so precise that VISAR measurements may also play a role in certifying beam-to-beam and shot-to-shot repeatability of NIF laser pulses. © 2001 American Institute of Physics.
Show PACS
52.35.Tc Shock waves and discontinuities
52.57.-z Laser inertial confinement
47.40.Nm Shock wave interactions and shock effects
07.60.Ly Interferometers

Core performance and mix in direct-drive spherical implosions with high uniformity

D. D. Meyerhofer, J. A. Delettrez, R. Epstein, V. Yu. Glebov, V. N. Goncharov, R. L. Keck, R. L. McCrory, P. W. McKenty, F. J. Marshall, P. B. Radha, S. P. Regan, S. Roberts, W. Seka, S. Skupsky, V. A. Smalyuk, et al.

Phys. Plasmas 8, 2251 (2001); http://dx.doi.org/10.1063/1.1350964 (6 pages) | Cited 54 times

Full Text: | Download PDF

Show Abstract
The performance of gas-filled, plastic-shell implosions has significantly improved with advances in on-target uniformity on the 60-beam OMEGA laser system [T. R. Boehly, D. L. Brown, R. S. Craxton et al., Opt. Commun. 133, 495 (1997)]. Polarization smoothing (PS) with birefringent wedges and 1-THz-bandwidth smoothing by spectral dispersion (SSD) have been installed on OMEGA. The beam-to-beam power imbalance is ⩽ 5% rms. Implosions of 20-μm-thick CH shells (15 atm fill) using full beam smoothing (1-THz SSD and PS) have primary neutron yields and fuel areal densities that are ∼ 70% larger than those driven with 0.35-THz SSD without PS. They also produce ∼ 35% of the predicted one-dimensional neutron yield. The results described here suggest that individual-beam nonuniformity is no longer the primary cause of nonideal target performance. A highly constrained model of the core conditions and fuel–shell mix has been developed. It suggests that there is a “clean” fuel region, surrounded by a mixed region, that accounts for half of the fuel areal density. © 2001 American Institute of Physics.
Show PACS
28.52.Cx Fueling, heating and ignition
52.50.Jm Plasma production and heating by laser beams (laser-foil, laser-cluster, etc.)
52.57.-z Laser inertial confinement
28.52.Fa Materials
52.70.Nc Particle measurements
52.50.Lp Plasma production and heating by shock waves and compression

Development and characterization of a Z-pinch-driven hohlraum high-yield inertial confinement fusion target concept

Michael E. Cuneo, Roger A. Vesey, John L. Porter, Gordon A. Chandler, David L. Fehl, Terrance L. Gilliland, David L. Hanson, John S. McGurn, Paul G. Reynolds, Laurence E. Ruggles, Hans Seamen, Rick B. Spielman, Ken W. Struve, William A. Stygar, Walter W. Simpson, et al.

Phys. Plasmas 8, 2257 (2001); http://dx.doi.org/10.1063/1.1348328 (11 pages) | Cited 62 times

Full Text: | Download PDF

Show Abstract
Initial experiments to study the Z-pinch-driven hohlraum high-yield inertial confinement fusion (ICF) concept of Hammer, Tabak, and Porter [Hammer et al., Phys. Plasmas 6, 2129 (1999)] are described. The relationship between measured pinch power, hohlraum temperature, and secondary hohlraum coupling (“hohlraum energetics”) is well understood from zero-dimensional semianalytic, and two-dimensional view factor and radiation magnetohydrodynamics models. These experiments have shown the highest x-ray powers coupled to any Z-pinch-driven secondary hohlraum (26±5 TW), indicating the concept could scale to fusion yields of >200 MJ. A novel, single-sided power feed, double-pinch driven secondary that meets the pinch simultaneity requirements for polar radiation symmetry has also been developed. This source will permit investigation of the pinch power balance and hohlraum geometry requirements for ICF relevant secondary radiation symmetry, leading to a capsule implosion capability on the Z accelerator [Spielman et al., Phys. Plasmas 5, 2105 (1998)]. © 2001 American Institute of Physics.
Show PACS
52.58.Lq Z-pinches, plasma focus, and other pinch devices
28.52.Cx Fueling, heating and ignition
28.52.Fa Materials
52.59.Qy Wire array Z-pinches
52.30.Cv Magnetohydrodynamics (including electron magnetohydrodynamics)

Fast ignitor research at the Institute of Laser Engineering, Osaka University

R. Kodama, K. Mima, K. A. Tanaka, Y. Kitagawa, H. Fujita, K. Takahashi, A. Sunahara, K. Fujita, H. Habara, T. Jitsuno, Y. Sentoku, T. Matsushita, T. Miyakoshi, N. Miyanaga, T. Norimatsu, et al.

Phys. Plasmas 8, 2268 (2001); http://dx.doi.org/10.1063/1.1352598 (7 pages) | Cited 43 times

Full Text: | Download PDF

Show Abstract
The physics element relevant to the fast ignitor in inertial confinement fusion has been extensively studied. Laser-hole boring with enormous photon pressures into overcritical densities was experimentally proved by density measurements with XUV laser probing. Ultra-intense laser interactions at a relativistic parameter regime were studied with a 50-TW glass laser system and a 100-TW glass laser system synchronized with a long pulse laser system. In the study of relativistic laser beam propagation in a 100-μm scale-length plasma, a special propagation mode (super-penetration mode) was observed, where the beam propagated into overdense regions close to the solid target surface. At the super-penetration mode, 20% of the laser energy converted to energetic electrons toward the target inside, while the coupling efficiency was 40% without the long scale-length plasmas. The high-density energetic electron transport and heating of solid material was also studied, indicating beamlike propagation of the energetic electrons in the solid target and effective heating of solid density ions with the electrons. Based on these basic experimental results, the heating of imploded plasma by short-pulse-laser light with three different ways of injecting the heating pulse has been studied. © 2001 American Institute of Physics.
Show PACS
52.57.Kk Fast ignition of compressed fusion fuels
52.50.Jm Plasma production and heating by laser beams (laser-foil, laser-cluster, etc.)
28.52.Cx Fueling, heating and ignition
52.25.-b Plasma properties
52.70.Kz Optical (ultraviolet, visible, infrared) measurements
52.27.Ny Relativistic plasmas
52.25.Fi Transport properties

Three-dimensional HYDRA simulations of National Ignition Facility targets

M. M. Marinak, G. D. Kerbel, N. A. Gentile, O. Jones, D. Munro, S. Pollaine, T. R. Dittrich, and S. W. Haan

Phys. Plasmas 8, 2275 (2001); http://dx.doi.org/10.1063/1.1356740 (6 pages) | Cited 30 times

Full Text: | Download PDF

Show Abstract
The performance of a targets designed for the National Ignition Facility (NIF) are simulated in three dimensions using the HYDRA multiphysics radiation hydrodynamics code. [M. Marinak et al., Phys. Plasmas 5, 1125 (1998)] In simulations of a cylindrical NIF hohlraum that include an imploding capsule, all relevant hohlraum features and the detailed laser illumination pattern, the motion of the wall material inside the hohlraum shows a high degree of axisymmetry. Laser light is able to propagate through the entrance hole for the required duration of the pulse. Gross hohlraum energetics mirror the results from an axisymmetric simulation. A NIF capsule simulation resolved the full spectrum of the most dangerous modes that grow from surface roughness. Hydrodynamic instabilities evolve into the weakly nonlinear regime. There is no evidence of anomalous low mode growth driven by nonlinear mode coupling. © 2001 American Institute of Physics.
Show PACS
28.52.Cx Fueling, heating and ignition
52.50.Jm Plasma production and heating by laser beams (laser-foil, laser-cluster, etc.)
52.65.-y Plasma simulation
52.35.Py Macroinstabilities (hydromagnetic, e.g., kink, fire-hose, mirror, ballooning, tearing, trapped-particle, flute, Rayleigh-Taylor, etc.)
52.35.Qz Microinstabilities (ion-acoustic, two-stream, loss-cone, beam-plasma, drift, ion- or electron-cyclotron, etc.)

Reflected shock experiments on the equation-of-state properties of liquid deuterium at 100–600 GPa (1–6 Mbar)

A. N. Mostovych, Y. Chan, T. Lehecha, L. Phillips, A. Schmitt, and J. D. Sethian

Phys. Plasmas 8, 2281 (2001); http://dx.doi.org/10.1063/1.1359444 (6 pages) | Cited 17 times

Full Text: | Download PDF

Show Abstract
Laser-driven shock experiments are used to study the equation-of-state (EOS) properties of liquid deuterium. Reflected shocks are utilized to increase the shock pressure, to expand the area of EOS phase space probed by the experiment, and to enhance the sensitivity to differences in compressibility. The results of these experiments differ substantially from the predictions of the Sesame EOS. EOS models showing large dissociation effects and large compressibility (up to a factor of 2) agree with the data. By use of independent techniques, this experiment offers the first confirmation of an earlier observation of enhanced compressibility in liquid deuterium. © 2001 American Institute of Physics.
Show PACS
62.50.-p High-pressure effects in solids and liquids
64.30.-t Equations of state of specific substances
64.70.-p Specific phase transitions

Growth of pellet imperfections and laser imprint in direct drive inertial confinement fusion targets

Andrew J. Schmitt, A. L. Velikovich, J. H. Gardner, C. Pawley, S. P. Obenschain, Y. Aglitskiy, and Y. Chan

Phys. Plasmas 8, 2287 (2001); http://dx.doi.org/10.1063/1.1360709 (9 pages) | Cited 20 times

Full Text: | Download PDF

Show Abstract
Simple hydrodynamic models for describing the Richtmyer–Meshkov (RM) growth and the Rayleigh–Taylor (RT) instability are tested by simulation. The RM sharp boundary model predictions are compared with numerical simulations of targets with surface perturbations or stationary intensity perturbations. Agreement is found in the overall trends, but the specific behavior can be significantly different. RM growth of imprint from optically smoothed lasers is also simulated and quantified. The results are used to calculate surface perturbations, growth factors, and laser imprint efficiencies. These in turn are used with standard RT growth formulas to predict perturbation growth in multimode simulations of compression and acceleration of planar and spherical targets. The largest differences between prediction and theory occur during ramp-up of the laser intensity, where RT formulas predict more growth than seen in the simulations. © 2001 American Institute of Physics.
Show PACS
52.57.Fg Implosion symmetry and hydrodynamic instability (Rayleigh-Taylor, Richtmyer-Meshkov, imprint, etc.)
47.40.Nm Shock wave interactions and shock effects

Ignition scaling laws and their application to capsule design

Mark C. Herrmann, Max Tabak, and John D. Lindl

Phys. Plasmas 8, 2296 (2001); http://dx.doi.org/10.1063/1.1364516 (9 pages) | Cited 25 times

Full Text: | Download PDF

Show Abstract
This paper investigates the amount of energy required to ensure the ignition of an inertial confinement fusion capsule. First, a series of one-dimensional LASNEX [G. B. Zimmerman and W. L. Kruer, Plasma Phys. Controlled Fusion 2, 51 (1975)] simulations are performed to create a database of barely ignited capsules that span the parameter regime of interest. This database is used to develop scaling laws for the ignition energy in terms of both the stagnated capsule parameters and the in-flight capsule parameters, and to explore the connection between these two parameter sets. We then examine how much extra energy is required to overcome the effect of the inevitable surface imperfections that are amplified during the implosion process. These perturbations can lead to break up of the capsule in flight or to mix of cold fuel into the hot spot, both of which can cause the capsule to fail. As an example, a family of capsules with fixed adiabat, drive pressure, and absorbed energy is studied; the capsule from this family that is maximally robust to these failure modes is found. © 2001 American Institute of Physics.
Show PACS
52.57.-z Laser inertial confinement
52.58.-c Other confinement methods
28.52.Cx Fueling, heating and ignition
52.65.-y Plasma simulation

One-, two-, and three-dimensional modeling of the different phases of wire array Z-pinch evolution

J. P. Chittenden, S. V. Lebedev, S. N. Bland, F. N. Beg, and M. G. Haines

Phys. Plasmas 8, 2305 (2001); http://dx.doi.org/10.1063/1.1343883 (10 pages) | Cited 39 times

Full Text: | Download PDF

Show Abstract
A series of one-, two-, and three-dimensional (1-D, 2-D, and 3-D) resistive magnetohydrodynamic models are used to build up a composite model of the different phases of wire array Z-pinch implosions. 1-D(r) and 2-D(r,z) “cold-start” simulations of single wire experiments are used to illustrate some of the important processes in the plasma formation phase of wire arrays. Detailed comparison of the simulation results with data from single wire experiments provides an excellent method of code verification. 2-D simulations in the r–θ or x–y plane show how the combination of the core–corona structure of the wire plasmas and the magnetic field topology result in the formation of radial plasma streams and a precursor plasma on axis well before the implosion phase commences. The same 2-D(x–y) model is also used to illustrate how the implosion trajectories of nested wire arrays are controlled by the levels of momentum, energy, and magnetic flux which are transferred during their collision. Preliminary results showing the evolution of a single wire in the array in 3-D are presented. These results suggest that the dynamics and structure of imploding wire arrays at Imperial College can potentially be explained in terms of the current breaking through the wire cores rather than in terms of the Rayleigh–Taylor instability. © 2001 American Institute of Physics.
Show PACS
52.55.Ez Theta pinch
52.65.-y Plasma simulation

Analysis of a direct-drive ignition capsule designed for the National Ignition Facility

P. W. McKenty, V. N. Goncharov, R. P. J. Town, S. Skupsky, R. Betti, and R. L. McCrory

Phys. Plasmas 8, 2315 (2001); http://dx.doi.org/10.1063/1.1350571 (8 pages) | Cited 100 times

Full Text: | Download PDF

Show Abstract
This paper reviews the current direct-drive ignition capsule designed for the National Ignition Facility (NIF) [M. D. Campbell and W. J. Hogan, Plasma Phys. Control. Fusion 41, B39 (1999)]. The ignition design consists of a cryogenic deuterium–tritium (DT) shell contained within a very thin CH shell. To maintain shell integrity during the implosion, the target is placed on an isentrope approximately three times that of Fermi-degenerate DT (α=3). One-dimensional studies show that the ignition design is robust. Two-dimensional simulations examine the effects on target performance due to laser imprint, power imbalance, and inner- and outer-target-surface roughness. Results from these studies indicate that the capsule gain can be scaled to the ice/vapor surface deformation at the end of the acceleration stage of the implosion. The physical reason for gain reduction as a function of increasing nonuniformities is examined. Simulations show that direct-drive target gains in excess of 30 can be achieved for an inner-ice-surface roughness of 1 μm rms, an on-target power imbalance of 2% rms, and by using the beam-smoothing technique SSD with 1 THz and two color cycles. © 2001 American Institute of Physics.
Show PACS
28.52.Cx Fueling, heating and ignition
52.57.-z Laser inertial confinement
52.50.Jm Plasma production and heating by laser beams (laser-foil, laser-cluster, etc.)

Fast particle generation and energy transport in laser-solid interactions

M. Zepf, E. L. Clark, K. Krushelnick, F. N. Beg, C. Escoda, A. E. Dangor, M. I. K. Santala, M. Tatarakis, I. F. Watts, P. A. Norreys, R. J. Clarke, J. R. Davies, M. A. Sinclair, R. D. Edwards, T. J. Goldsack, et al.

Phys. Plasmas 8, 2323 (2001); http://dx.doi.org/10.1063/1.1351824 (8 pages) | Cited 55 times

Full Text: | Download PDF

Show Abstract
The generation of MeV electron and ion beams using lasers with intensities of up to 1020 W cm−2 is reported. Intense ion beams with high energies (up to 40 MeV and to 3×1012 protons >5 MeV) are observed. The properties of these particle beams were measured in considerable detail and the results are compared to current theoretical explanations for their generation. © 2001 American Institute of Physics.
Show PACS
52.50.Jm Plasma production and heating by laser beams (laser-foil, laser-cluster, etc.)
52.70.Nc Particle measurements
52.25.Fi Transport properties

Optical and plasma smoothing of laser imprinting in targets driven by lasers with SSD bandwidths up to 1 THz

T. R. Boehly, V. N. Goncharov, O. Gotchev, J. P. Knauer, D. D. Meyerhofer, D. Oron, S. P. Regan, Y. Srebro, W. Seka, D. Shvarts, S. Skupsky, and V. A. Smalyuk

Phys. Plasmas 8, 2331 (2001); http://dx.doi.org/10.1063/1.1352616 (7 pages) | Cited 14 times

Full Text: | Download PDF

Show Abstract
The creation of a plasma atmosphere in laser-target interactions increases the distance between the regions of laser absorption and hydrodynamic instability (ablation front), thus allowing thermal smoothing and a reduction of laser-imprinted modulations that reach the unstable ablation region. The total laser imprinting is reduced with pulse shapes that produce a plasma atmosphere more rapidly and by the implementation of temporal beam smoothing. These effects are measured and found to be consistent with models for the hydrodynamics and optical smoothing by spectral dispersion (SSD). Imprinting is reduced as the laser bandwidth is increased from 0.2 to 1.0 THz. © 2001 American Institute of Physics.
Show PACS
52.50.Jm Plasma production and heating by laser beams (laser-foil, laser-cluster, etc.)
52.35.Py Macroinstabilities (hydromagnetic, e.g., kink, fire-hose, mirror, ballooning, tearing, trapped-particle, flute, Rayleigh-Taylor, etc.)

Long term instability growth of radiatively driven thin planar shells

R. J. Mason, D. E. Hollowell, G. T. Schappert, and S. H. Batha

Phys. Plasmas 8, 2338 (2001); http://dx.doi.org/10.1063/1.1354150 (6 pages) | Cited 6 times

Full Text: | Download PDF

Show Abstract
The Rayleigh–Taylor instability of radiatively driven thin copper foils is studied under pure ablation, as well as with beryllium buffers to provide additional pressure drive, in support of the target design for Inertial Confinement Fusion. Modeling was done with the RAGE adaptive mesh refinement code [R. M. Baltrusaitis, M. L. Gittings, R. P. Weaver, R. F. Benjamin, and J. M. Budzinski, Phys. Fluids 8, 2471 (1996)] of experiments done on the OMEGA [T. R. Boehly, D. L. Brown, R. S. Craxton et al., Opt. Commun. 133, 495 (1997)] laser. The copper foils were typically 11.5 μm thick with 0.45 μm amplitude and 45 μm wavelength cosine surface perturbations. The beryllium layer was 5 μm thick. The drive was a “PS26”-like [J. D. Lindl, Phys. Plasmas 2, 3933 (1995)] laser pulse delivering peak 160–185 eV radiation temperatures. Good agreement between experiment and simulation has been obtained out to 4.5 ns. Mechanisms for late time agreement are discussed. © 2001 American Institute of Physics.
Show PACS
52.57.-z Laser inertial confinement
52.35.Py Macroinstabilities (hydromagnetic, e.g., kink, fire-hose, mirror, ballooning, tearing, trapped-particle, flute, Rayleigh-Taylor, etc.)
52.38.-r Laser-plasma interactions
52.50.Jm Plasma production and heating by laser beams (laser-foil, laser-cluster, etc.)

The ablation-front Rayleigh–Taylor dispersion curve in indirect drive

K. S. Budil, B. Lasinski, M. J. Edwards, A. S. Wan, B. A. Remington, S. V. Weber, S. G. Glendinning, L. Suter, and P. E. Stry

Phys. Plasmas 8, 2344 (2001); http://dx.doi.org/10.1063/1.1356738 (5 pages) | Cited 13 times

Full Text: | Download PDF

Show Abstract
The Rayleigh–Taylor (RT) instability, which occurs when a lower-density fluid accelerates a higher-density layer, is common in nature. At an ablation front a sharp reduction in the growth rate of the instability at short wavelengths can occur, in marked contrast to the classical case where growth rates are highest at the shortest wavelengths. Theoretical and numerical investigations of the ablative RT instability are numerous and differ considerably on the level of stabilization expected. Presented here are the results of a series of laser experiments designed to measure the RT dispersion curve for a radiatively driven sample. Aluminum foils with imposed sinusoidal perturbations ranging in wavelength from 10 to 70 μm were ablatively accelerated with a radiation drive generated in a gold cylindrical hohlraum. A strong shock wave compresses the package followed by an ∼ 2 ns period of roughly constant acceleration and the experiment is diagnosed via face-on radiography. Perturbations with wavelengths ≥ 20 μm experienced substantial growth during the acceleration phase while shorter wavelengths showed a sharp drop off in overall growth. These experimental results compared favorably to calculations with a two-dimensional radiation-hydrodynamics code, however, the growth is significantly affected by the rippled shock launched by the drive. Due to the influence of the rippled shock transit phase of the experiment and ambiguities associated with directly extracting the physical amplitude of the perturbations at the ablation front from the simulations, direct comparison to the ablation front RT theory of Betti et al. [Phys. Plasmas 5, 1446 (1998)], was difficult. Instead, a numerical “experiment” was constructed that minimized the influence of the shock and this was compared to the Betti model showing quite good agreement. © 2001 American Institute of Physics.
Show PACS
52.58.Qv Electrostatic and high-frequency confinement
52.35.Tc Shock waves and discontinuities
52.50.Lp Plasma production and heating by shock waves and compression
52.35.Py Macroinstabilities (hydromagnetic, e.g., kink, fire-hose, mirror, ballooning, tearing, trapped-particle, flute, Rayleigh-Taylor, etc.)
52.80.Qj Explosions; exploding wires
28.52.Cx Fueling, heating and ignition

Stimulated photon cascade and condensate in a relativistic laser-plasma interaction

K. Mima, M. S. Jovanović, Y. Sentoku, Z.-M. Sheng, M. M. Škorić, and T. Sato

Phys. Plasmas 8, 2349 (2001); http://dx.doi.org/10.1063/1.1356741 (8 pages) | Cited 34 times

Full Text: | Download PDF

Show Abstract
The propagation of a linearly polarized relativistic laser pulse in an underdense plasma is studied by fluid-Maxwell and particle-in-cell simulations. A nonlinear interplay between backward and forward stimulated Raman scattering instabilities produces a strong spatial modulation of the light pulse and the down cascade in its frequency spectrum. The Raman cascade saturates by a unique photon condensation at the bottom of the light spectra near the electron plasma frequency, related to strong depletion and possible break-up of the laser beam. In the final stage of the cascade-into-condensate mechanism, the depleted downshifted laser pulse is gradually transformed into a train of ultra-short relativistic light solitons. © 2001 American Institute of Physics.
Show PACS
42.65.Dr Stimulated Raman scattering; CARS
42.65.Es Stimulated Brillouin and Rayleigh scattering
52.38.Bv Rayleigh scattering; stimulated Brillouin and Raman scattering
52.38.Dx Laser light absorption in plasmas (collisional, parametric, etc.)
52.65.-y Plasma simulation
42.65.Tg Optical solitons; nonlinear guided waves
52.35.Py Macroinstabilities (hydromagnetic, e.g., kink, fire-hose, mirror, ballooning, tearing, trapped-particle, flute, Rayleigh-Taylor, etc.)
52.27.Ny Relativistic plasmas

National Ignition Facility scale hohlraum asymmetry studies by thin shell radiography

S. M. Pollaine, D. K. Bradley, O. L. Landen, R. J. Wallace, O. S. Jones, P. A. Amendt, L. J. Suter, and R. E. Turner

Phys. Plasmas 8, 2357 (2001); http://dx.doi.org/10.1063/1.1364514 (8 pages) | Cited 22 times

Full Text: | Download PDF

Show Abstract
A necessary condition for igniting indirectly driven inertial confinement fusion (ICF) capsules on the National Ignition Facility (NIF) is controlling drive asymmetry to the 1% level [S. W. Haan, S. M. Pollaine, J. D. Lindl et al., Phys. Plasmas 2, 2480 (1995)]. Even flux-asymmetry modes (e.g., Legendre modes P2, P4, P6, and P8) must be reduced by hohlraum design and laser beam pointing. Odd flux-asymmetry modes (e.g., Legendre modes P1, P3, P5, etc.) are theoretically removed by reflection symmetry across the hohlraum midplane [S. M. Pollaine and D. Eimerl, Nucl. Fusion 38, 1523 (1998)], but will be produced by power imbalance, laser beam pointing errors, and target fabrication errors. An experimental campaign is now being conducted on the University of Rochester’s Omega laser to measure higher order (P4 and higher) flux asymmetry modes inside hohlraums that approximate the conditions of a NIF hohlraum during the 90 eV early drive phase [S. W. Haan, S. M. Pollaine, J. D. Lindl et al., Phys. Plasmas 2, 2480 (1995)]. These experiments use a new point-projection backlighting technique [O. L. Landen, D. R. Farley, S. G. Glendinning et al., Rev. Sci. Instrum. 72, 627 (2001)] to cast high quality 4.7 keV radiographs of thin 2 mm diameter Ge-doped CH shells designed to enhance sensitivity to drive asymmetries. Distortions in the position of the limb of the shells resulting primarily from drive asymmetries are measured to an accuracy of 2 μm. The linearity and sensitivity of thin imploding shells to flux asymmetry makes it possible to achieve this degree of accuracy, which is sufficient for NIF ignition symmetry tuning. The promising results to date permit the comparison of measured and predicted distortions and, by inference, drive asymmetries for the first eight asymmetry modes. © 2001 American Institute of Physics.
Show PACS
52.57.-z Laser inertial confinement
52.50.Jm Plasma production and heating by laser beams (laser-foil, laser-cluster, etc.)
28.52.Cx Fueling, heating and ignition
52.70.La X-ray and γ-ray measurements
Return to All Sections
Close

Google Calendar

ADVERTISEMENT

Go to AIP Home   © AIP Publishing LLC
close