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Developing beam phasing on the Nova laser

Description: We are presently adding the capability to irradiate indirectly-driven Nova targets with two rings of illumination inside each end of the hohlraum for studies of time-dependent second Legendre (P2) and time- integrated fourth Legendre (P4) flux asymmetry control. The rings will be formed with specially designed kinoform phase plates (KPPs), which will direct each half of each beam into two separate rings that are nearly uniform azimuthally. The timing and temporal pulse shape of the outer rings will be controlled independently from those of the inner rings, allowing for phasing of the pulse shapes to control time dependent asymmetry. Modifications to the incident beam diagnostics (IBDS) will enable us to verify that acceptable levels of power balance among the contributing segments of each ring have been achieved on each shot. Current techniques for precision beam pointing and timing are expected to be sufficiently accurate for these experiments. We present a design for an affordable retrofit to achieve beam phasing on Nova, results of a simplified demonstration, and calculations highlighting the anticipated benefits.
Date: March 10, 1997
Creator: Ehrlich, R.B.; Amendt, P.A.; Dixit, S.N.; Hammel, B.A.; Kalantar, D.H.; Pennington, D.M. et al.
Partner: UNT Libraries Government Documents Department

Nuclear diagnostics for inertial confinement fusion implosions

Description: This abstract contains viewgraphs on nuclear diagnostic techniques for inertial confinement fusion implosions. The viewgraphs contain information on: reactions of interest in ICF; advantages and disadvantages of these methods; the properties nuclear techniques can measure; and some specifics on the detectors used.
Date: November 1, 1997
Creator: Murphy, T.J.
Partner: UNT Libraries Government Documents Department

LLE review. Volume 66. Quarterly report, January--March 1996

Description: This volume of the LLE Review, covering the period January-March 1996, contains three articles related to spherical implosions and their diagnosis, one article that provides an analysis of laser-plasma interactions, and three articles on advanced technologies developed at LLE.
Date: June 1, 1996
Creator: Boehly, T.R.
Partner: UNT Libraries Government Documents Department

Derivation of preliminary specifications for transmitted wavefront and surface roughness for large optics used in inertial confinement fusion

Description: In preparation for beginning the design of the Nation Ignition Facility (NIF) in the United States and the Laser Mega-Joule (LMJ) in France, the authors are in the process of deriving new specifications for the large optics required for these facilities. Traditionally, specifications for transmitted wavefront and surface roughness of large ICF optics have been based on parameters which were easily measured during the early 1980`s, such as peak-to-valley wavefront error (PV) and root-mean-square (RMS) surface roughness, as well as wavefront gradients in terms of waves per cm. While this was convenient from a fabrication perspective, since the specifications could be easily interpreted by fabricators in terms which were understood and conventionally measurable, it did not accurately reflect the requirements of the laser system. For the NIF and LMJ laser systems, the authors use advances in metrology and interferometry and an enhanced understanding of laser system performance to derive specifications which are based on power spectral densities (PSD`s.) Such requirements can more accurately reflect the requirements of the laser system for minimizing the amplitude of mid- and high-spatial frequency surface and transmitted wavefront errors, while not over constraining the fabrication in terms of low spatial frequencies, such as residual coma or astigmatism, which are typically of a very large amplitude compared to periodic errors. In order to study the effect of changes in individual component tolerances, it is most useful to have a model capable of simulating real behavior. The basis of this model is discussed in this paper, outlining the general approach to the {open_quotes}theoretical{close_quotes} study of ICF optics specifications, and an indication of the type of specification to be expected will be shown, based upon existing ICF laser optics.
Date: June 27, 1995
Creator: Aikens, D.; Roussel, A. & Bray, M.
Partner: UNT Libraries Government Documents Department

Experimental and numerical investigation of shock wave propagation through complex geometry, gas continuous, two-phase media

Description: The work presented here investigates the phenomenon of shock wave propagation in gas continuous, two-phase media. The motivation for this work stems from the need to understand blast venting consequences in the HYLIFE inertial confinement fusion (ICF) reactor. The HYLIFE concept utilizes lasers or heavy ion beams to rapidly heat and compress D-T targets injected into the center of a reactor chamber. A segmented blanket of falling molten lithium or Li{sub 2}BeF{sub 4} (Flibe) jets encircles the reactor`s central cavity, shielding the reactor structure from radiation damage, absorbing the fusion energy, and breeding more tritium fuel. X-rays from the fusion microexplosion will ablate a thin layer of blanket material from the surfaces which face toward the fusion site. This generates a highly energetic vapor, which mostly coalesces in the central cavity. The blast expansion from the central cavity generates a shock which propagates through the segmented blanket - a complex geometry, gas-continuous two-phase medium. The impulse that the blast gives to the liquid as it vents past, the gas shock on the chamber wall, and ultimately the liquid impact on the wall are all important quantities to the HYLIFE structural designers.
Date: December 31, 1993
Creator: Chien-Chih Liu, J.
Partner: UNT Libraries Government Documents Department

Computer simulation of laser-driven implosion of DT-filled glass microballoons

Description: The results of some experimental measurements of laser implosions are analyzed. Calculations are made of specific target irradiations and compared with experiments. A general description is given of exploding pushers and the physical processes involved are described. (MOW)
Date: October 17, 1975
Creator: Larsen, J.T.
Partner: UNT Libraries Government Documents Department

Estimated refractive index and solid density of DT, with application to hollow-microsphere laser targets

Description: The literature values for the 0.55-$mu$m refractive index N of liquid and gaseous H$sub 2$ and D$sub 2$ are combined to yield the equation (N - 1) = [(3.15 +- 0.12) x 10$sup -6$]rho, where rho is the density in moles per cubic meter. This equation can be extrapolated to 300$sup 0$K for use on DT in solid, liquid, and gas phases. The equation is based on a review of solid-hydrogen densities measured in bulk and also by diffraction methods. By extrapolation, the estimated densities and 0.55-$mu$m refractive indices for DT are given. Radiation-induced point defects could possibly cause optical absorption and a resulting increased refractive index in solid DT and T$sub 2$. The effect of the DT refractive index in measuring glass and cryogenic DT laser targets is also described. (auth)
Date: September 16, 1975
Creator: Briggs, C.K.; Tsugawa, R.T.; Hendricks, C.D. & Souers, P.C.
Partner: UNT Libraries Government Documents Department

Argus target chamber

Description: A target chamber for application in the laser fusion program must satisfy some very basic requirements. (1) Provide a vacuum on the order of 10$sup -6$ torr. (2) Support a microscopically small target in a fixed point in space and verify its location within 5 micrometers. (3) Contain an adjustable beam focusing system capable of delivering a number of laser beams onto the target simultaneously, both in time and space. (4) Provide access for diagnostics to evaluate the results of target irradiation. (5) Have flexibility to allow changes in targets, focusing optics and number of beams. The ARGUS laser which is now under construction at LLL will have a target chamber which meets these requirements in a simple economic manner. The chamber and auxiliary equipment are described, with reference to two double beam focusing systems; namely, lenses and ellipsoidal mirrors. Provision is made for future operation with four beams, using ellipsoidal mirrors for two-sided illumination and lens systems for tetragonal and tetrahedral irradiation. (auth)
Date: November 12, 1975
Creator: Rienecker, F. Jr.; Glaros, S.S. & Kobierecki, M.
Partner: UNT Libraries Government Documents Department

Preheat effects on microballoon laser fusion implosions

Description: Nonequilibrium hydroburn simulations of early laser-driven compression experiments indicate that low energy photons from the vicinity of the ablation surface are preheating the microballoon-pushers, thereby severely limiting the compressions achieved (similar degradation may result from 1 to 4 percent energy deposition by superthermal electrons). This implies an 8- to 27-fold increase in the energy requirements for breakeven, unless radiative preheat can be drastically reduced by, say, the use of composite ablator-pushers. (auth)
Date: July 1, 1975
Creator: Fraley, G.S. & Mason, R.J.
Partner: UNT Libraries Government Documents Department

Thermal recovery measurements on multi-segment amplifiers

Description: We present the results of a series of experiments to measure the thermal recovery times of a flashlamp-pumped, Nd:Glass multi-segment laser amplifier. In particular, we investigated the thermal recovery times under the following cooling options: (1) passive cooling; (2) active cooling of the flashlamp cassettes, and (3) active cooling of the flashlamp cassettes and gas flow in the pump cavity.
Date: September 21, 1995
Creator: Rotter, M.D.; McCracken, R.W.; Erlandson, A.C. & Brown, D.
Partner: UNT Libraries Government Documents Department