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Recent developments in laser plasma theory and simulations

Description: The principal recent developments are that (1) nonlinear steepening of the density profile strongly modifies absorption processes near the critical density, (2) a sizeable stimulated reflection of light can occur; and (3) energy transport by hot electrons is impeded either by the need to draw a return current, by ion fluctuations generated by this return current, or by self- generated magnetic fields. A brief overview of these results is presented.
Date: January 1, 1975
Creator: Kruer, W. L.
Partner: UNT Libraries Government Documents Department

Theory and simulation of laser plasma coupling-II

Description: In previous lectures at the 1979 Scottish Universities' Summer School in Physics, we presented an introduction to the theory and simulation of laser plasma interactions. A representative mix of coupling processes was discussed. In this update lecture for the 1982 school, we will emphasize two specific topics which have received increased attention in the last few years: stimulated Raman scatter and the wavelength scaling of laser plasma coupling.
Date: July 29, 1982
Creator: Kruer, W.L.
Partner: UNT Libraries Government Documents Department

Laser-plasma coupling

Description: The following topics are discribed: (1) ionization of target, (2) electromagnetic wave propagation in plasma, (3) collisional absorption, (4) light absorption in collisionless plasma, (5) resonance absorption, (6) instabilities, (7) Brillowin instability, and (8) some other effects. (MOW
Date: November 14, 1978
Creator: Kruer, W.L.
Partner: UNT Libraries Government Documents Department

Theory and simulation of laser plasma coupling

Description: The theory and simulation of these coupling processes are considered. Particular emphasis is given to their nonlinear evolution. First a brief introduction to computer simulation of plasmas using particle codes is given. Then the absorption of light via the generation of plasma waves is considered, followed by a discussion of stimulated scattering of intense light. Finally these calculations are compared with experimental results.
Date: August 9, 1979
Creator: Kruer, W.L.
Partner: UNT Libraries Government Documents Department

Thresholds of Raman backscatter: effects of collisions and Landau damping

Description: We present 1.5 dimensional simulations and theory of the threshold of Raman backscatter for a variety of density profiles, background temperatures and collision frequencies, nu/sub ei/. The simulations show Raman backscatter of approx. 4 x 10/sup -4/ at intensities approx. 30 times below the del n threshold which we suggest is due to light scattering off of noise electron plasma waves. The absorption drops significantly and the threshold rises as the Landau damping ..omega../sub i/ and/or nu/sub ei/ approach the growth rate ..gamma../sub 0/. Many experiments are already in the collisional regime.
Date: November 3, 1983
Creator: Estabrook, K. & Kruer, W.L.
Partner: UNT Libraries Government Documents Department

Deflection, spraying, and induced scattering of intense laser beams in plasmas

Description: Investigations into laser beam spraying, deflection, and induced scattering in plasmas are presented. Recent calculations and experiments on beam spraying due to filamentation are discussed. A simple model is presented for an enhanced beam deflection associated with nearly sonic plasma flow transverse to the beam. This model provides useful insights on the laser beam deflection, its scaling and the importance of self-consistent profile modifications. Finally, some discussion is given of recent experiments demonstrating the interplay between stimulated.Raman and Brillouin scattering.
Date: September 1, 1996
Creator: Kruer, W.L.
Partner: UNT Libraries Government Documents Department

Control of laser plasma instabilities in hohlraums

Description: Laser plasma instabilities are an important constraint on the operating regime for inertial fusion. Many techniques have been developed to control the various laser-driven instabilities. Experiments with long scale length plasmas are testing these instability levels, the nonlinear regimes, and the control mechanisms.
Date: December 1, 1996
Creator: Kruer, W.L.
Partner: UNT Libraries Government Documents Department

Laser plasma interactions in hohlraums

Description: Lasers plasma instabilities are an important constraint in x-ray driven inertial confinement fusion. In hohlraums irradiated with 1.06 {mu}m light on the Shiva laser, plasma instabilities were extremely deleterious, driving the program to the use of shorter wavelength light. Excellent coupling has been achieved in hohlraums driven with 0.35 {mu}m light on the Nova laser. Considerable attention is being given to the scaling of this excellent coupling to the larger hohlraums for an ignition target. Various instability control mechanisms such as large plasma wave damping and laser beam incoherence are discussed, as well as scaling experiments to check the instability levels.
Date: October 5, 1994
Creator: Kruer, W.L.
Partner: UNT Libraries Government Documents Department

Electromagnetic effects in relativistic electron beam plasma interactions

Description: Electromagnetic effects excited by intense relativistic electron beams in plasmas are investigated using a two-dimensional particle code. The simulations with dense beams show large magnetic fields excited by the Weibel instability as well as sizeable electromagnetic radiation over a significant range of frequencies. The possible relevance of beam plasma instabilities to the laser acceleration of particles is briefly discussed. 6 refs., 4 figs.
Date: February 13, 1985
Creator: Kruer, W.L. & Langdon, A.B.
Partner: UNT Libraries Government Documents Department

Heating by the Raman instability

Description: Computer simulations are presented of the reflection and heating due to stimulated Raman backscatter of intense laser light in large regions of underdense plasma. The heated electron distribution is found to be approximately a Maxwellian of temperature (m/sub e//2)v/sub p//sup 2/, where v/sub p/ is the phase velocity of the electron plasma wave. A simple model of the reflection is presented. Raman may cause a pre-heat problem with large laser fusion reactor targets.
Date: April 11, 1980
Creator: Estabrook, K.G. & Kruer, W.L.
Partner: UNT Libraries Government Documents Department

Harmonic generation of ion waves due to Brillouin backscattering

Description: We report results of simulations of stimulated Brillouin backscatter in which we see the second spatial harmonic of the ion density fluctuation and compare with linear, fluid theory. We also describe examples of the competition between Raman and Brillouin backscatter. 21 refs., 3 figs.
Date: May 22, 1985
Creator: Estabrook, K.; Kruer, W.L. & Haines, M.G.
Partner: UNT Libraries Government Documents Department

Brillouin scatter in laser-produced plasmas

Description: The absorption of intense laser light is found to be reduced when targets are irradiated by 1.06 ..mu..m light with long pulse widths (150-400 psec) and large focal spots (100-250 ..mu..m). Estimates of Brillouin scatter which account for the finite heat capacity of the underdense plasma predict this reduction. Spectra of the back reflected light show red shifts indicative of Brillouin scattering.
Date: July 18, 1977
Creator: Phillion, D.W.; Kruer, W.L. & Rupert, V.C.
Partner: UNT Libraries Government Documents Department

Laser Plasma instability reduction by coherence disruption

Description: The saturation levels of stimulated scattering of intense laser light in plasmas and techniques to reduce these levels are of great interest. A simple model is used to highlight the dependence of the reflectivity on the coherence length for the density fluctuations producing the scattering. Sometimes the coherence lengths can be determined nonlinearly. For NIF hohlraum plasmas, a reduction in the coherence lengths might be engineered in several ways. Finally, electron trapping in ion sound waves is briefly examined as a potentially important effect for the saturation of stimulated Brillouin scattering.
Date: April 19, 2006
Creator: Kruer, W l; Amendt, P A; Meezan, N & Suter, L J
Partner: UNT Libraries Government Documents Department

Comparison of LASNEX calculations with experimental results of parylene disc irradiations at 1.06 $mu$m

Description: Calculations are discussed using the 2D Lagrangian code LASNEX to simulate irradiation of Parylene discs. Using a representation of the experimental beam profile, geometric optics propagation, and an absorption model based on plasma simulations, the scattered light angular intensity distribution can be obtained. The use of a suprathermal electron heating spectrum and thermally generated magnetic fields with Braginskii transport coefficients leads to agreement with time-integrated x-ray spectra and x-ray spatial distributions. Details of the calculations and comparisons with other models are discussed. (auth)
Date: November 1, 1975
Creator: Mead, W.C.; Kruer, W.L.; Lindl, J.D. & Shay, H.D.
Partner: UNT Libraries Government Documents Department

Absorption of laser light in overdense plasmas by sheath inverse bremsstrahlung

Description: The original sheath inverse bremsstrahlung model [P. J. Catto and R. M. More, 1977] is modified by including the vxB term in the equation of motion. It is shown that the present results axe significantly different from those derived without the vxB term. The vxB term is also important in interpreting the absorption mechanism. If the vxB term were neglected, the absorption of the light would be incorrectly interpreted as an increase in the transverse electron temperature. This would violate the conservation of the transverse components of the canonical momentum, in the case of a normally incident laser light. It is also shown that both the sheath inverse bremsstrahlung and the anomalous skin effect are limiting cases of the same collisionless absorption mechanism. Finally, results from PIC plasma simulations are compared with the absorption coefficient calculated from the linear theory.
Date: November 1, 1994
Creator: Yang, T.Y.B.; Kruer, W.L. & More, R.M.
Partner: UNT Libraries Government Documents Department

Collisionless absorption of light waves incident on overdense plasmas with steep density gradients

Description: Collisionless absorption of laser light incident on overdense plasmas with steep density gradients is studied analytically and numerically. For the normal incidence case, it is shown that both sheath inverse bremsstrahlung and the anomalous skin effect are limiting cases of the same collisionless absorption mechanism. Using particle-in-cell (PIC) plasma simulations, the effects of finite sheath-transit time and finite density gradient are investigated. The analyses are extended to oblique incident cases. For p-polarized obliquely incident light, the results are significantly different from those for the normal incidence case. Most noticeable is the absorption enhancement for the p-polarized light due to the interaction of the electrons with the normal (parallel to the density gradient) component of the laser electric field in the sheath region.
Date: July 31, 1995
Creator: Yang, T. Y. B.; Kruer, W. L. & Langdon, A. B.
Partner: UNT Libraries Government Documents Department

Sources of hot electrons in laser-plasma interaction with emphasis on Raman and turbulence absorption

Description: Heating targets with high power lasers results in a sizable fraction of the absorbed energy going into electrons of temperature much greater than thermal which can pre-heat the pellet core and accelerate fast ion blowoff which results in poor momentum transfer and hence poor compression efficiency. The present emphasis is to build lasers of higher frequency, ..omega../sub 0/, which at the same W/cm/sup 2/ results in more absorption into cooler electrons. Two physical reasons are that the laser can propagate to a higher electron density, n, infinity..omega../sub 0//sup 2/ resulting in more collisional inverse bremsstrahlung absorption proportional to n, and because the hot temperatures from some plasma absorption processes increase as the oscillatory velocity of an electron in the laser electric field v/sub 0//c = eE/(m/sub e/..omega../sub 0/). The heated electron temperatures from other plasma processes (Raman for example approx.(m/sub e//2)v/sup 2//sub phase/ and the higher laser frequency helps by increasing the competing collisional absorption and decreasing the Raman gain.
Date: April 6, 1982
Creator: Estabrook, K.; Kruer, W.L.; Phillion, D.W.; Turner, R.E. & Campbell, E.M.
Partner: UNT Libraries Government Documents Department

Ultra-intense, short pulse laser-plasma interactions with applications to the fast ignitor

Description: Due to the advent of chirped pulse amplification (CPA) as an efficient means of creating ultra-high intensity laser light (I > 5{times}10{sup 17} W/cm{sup 2}) in pulses less than a few picoseconds, new ideas for achieving ignition and gain in DT targets with less than 1 megajoule of input energy are currently being pursued. Two types of powerful lasers are employed in this scheme: (1) channeling beams and (2) ignition beams. The current state of laser-plasma interactions relating to this fusion scheme will be discussed. In particular, plasma physics issues in the ultra-intense regime are crucial to the success of this scheme. We compare simulation and experimental results in this highly nonlinear regime.
Date: April 1, 1995
Creator: Wilks, S. C.; Kruer, W. L.; Young, P. E.; Hammer, J. & Tabak, M.
Partner: UNT Libraries Government Documents Department

Parametric instabilities in laser/matter interaction: from noise levels to relativistic regimes

Description: The purpose of this LDRD was the study of parametric instabilities on a laser-produced plasma, addressing crucial issues affecting the coupling between the laser and the plasma. We have made very good progress during these three years, in advancing our understanding in many different fronts. Progress was made in both theoretical and experimental areas. The coupling of high-power laser light to a plasma through scattering instabilities is still one of the most complex processes in laser-plasma interaction physics. In spite of the relevance of these parametric processes to inertial confinement fusion (ICF) and all other situations where a high-power laser beam couples to a plasma, many aspects of the interaction remain unexplained, even after many years of intensive experimental and theoretical efforts. Important instabilities under study are stimulated Brillouin scattering (SBS), stimulated Raman scattering (SRS), and the Langmuir decay instability (LDI). The study of these instabilities is further complicated by the competition and interplay between them, and, in the case of ICF, by the presence of multiple overlapping interaction beams. Stimulated Brillouin scattering consists of the decay of the incident electromagnetic (EM) wave into a scattered EM wave and an ion acoustic wave (IAW). Similarly, SRS consists of the decay of the incident EM wave into a scattered EM wave and an electron plasma wave (EPW). Langmuir decay instability is the further decay of an EPW into a secondary EPW and an IAW. The principal areas of research covered during this three-year period were the following: a) Modeling of Parametric Instabilities in Speckles b) Langmuir Decay Instability c) Non Maxwellian Plasmas d) Multiple Interaction Beams e) SBS from Speckle Distributions.
Date: February 11, 1999
Creator: Baldis, H A; Kruer, W L & Labaune, C L
Partner: UNT Libraries Government Documents Department


Description: We present experimental data of electron energy distributions from ultra-intense (>10{sup 19} W/cm{sup 2}) laser-solid interactions using the Rutherford Appleton Laboratory Vulcan petawatt laser. These measurements were made using a CCD-based magnetic spectrometer. We present details on the distinct effective temperatures that were obtained for a wide variety of targets as a function of laser intensity. It is found that as the intensity increases from 10{sup 17} W/cm{sup 2} to 10{sup 19} W/cm{sup 2}, a 0.4 dependence on the laser intensity is found. Between 10{sup 19} W/cm{sup 2} and 10{sup 20} W/cm{sup 2}, a gradual rolling off of temperature with intensity is observed.
Date: December 8, 2005
Creator: Chen, H; Wilks, S C; Kruer, W L; Moon, S; Patel, N; Patel, P K et al.
Partner: UNT Libraries Government Documents Department