Timeline Archives - Page 13 of 18 - Laboratory for Laser Energetics

Diagnosing High Density Using Fusion

March 1, 1988/in Timeline/by Rodi Keisidis

1988:

The DT fuel density in high-compression experiments at LLE was measured using the “knock-on” diagnostic. Previously, this diagnostic had been used only in low-density experiments where there was a negligible amount of slowing of the knock-on particles within the target. In the experiments, the target density-radius product (ρR) was sufficiently large to significantly moderate the knock-on particles. So a new technique had to be developed to accommodate the distorted spectrum.

A technique was developed to measure fuel ρR with knock-on particles in a model-independent way for experiments where the total target ρR is less than ~50 mg/cm². The technique takes into consideration moderation of the knock-on within the target and is independent of the moderation source whether it is in the fuel or shell. Even if there is mixing between the fuel and shell, the diagnostic measures the ρR of the fuel portion. In addition, the ρR of the shell can be estimated by demanding consistency among the number of tracks in different foils.

Phase Conversion with Distributed Phase Plates

February 1, 1988/in Timeline/by Rodi Keisidis

1988:

An alternative to phase correcting a wavefront involves modifying the laser beam’s coherence properties, thereby changing its focusing characteristics. A phase-conversion technology that incorporates a distribution of near-field phases to perform either static phase correction or induce spatial incoherence offers a degree of flexibility needed at this stage of research. Distributed-phase-plate technology, deployed on the OMEGA Laser System, offers this parallel route toward increasingly higher levels of irradiation uniformity.

The joining of many diverse technologies resulted in the design, fabrication, and testing of high-quality distributed phase plates (DPP’s). Computerized image generation, photolithography, chemical vapor deposition, and high-resolution interferometry were combined to make OMEGA the only frequency-tripled and phase-converted laser system. DPP’s improved the irradiation uniformity at the target plane by more than a factor of 3. The increased reproducibility of the beam profiles offered by the DPP’s made possible the more-critical assessment of shot-to-shot variations in beam energy and beam pointing.

OMEGA Experiments Show 200x Liquid-DT Density

January 1, 1988/in Timeline/by Rodi Keisidis

1988:

In 1988, with an adapted cryogenic system and newly developed beam smoothing, LLE demonstrated 100 to 200x liquid-DT density implosions on OMEGA. An extensive array of experimental diagnostics was employed to carry out these experiments including absorption and fractional conversion of the absorbed energy into x rays; time- and space-resolved measurements of x-ray emissions; neutron yield and energy spectrum; and fuel-areal-density measurements using knock-on diagnostics. The knock-on diagnostics technique conceived and developed at LLE, in particular, gave unequivocal evidence of high density. It was the only diagnostic that could measure density in a temperature-independent way. The experimental results were validated by an independent DOE panel in March 1988. This was the highest compressed-fuel density record in ICF experiments using either the direct or indirect approach at that time and made a strong case for the direct-drive approach.

“Laser Driven Implosion of Thermonuclear Fuel to 20 to 40 g cm^-3” by R. L. McCrory et al.published in the September 1988 issue of Nature, highlighted this achievement.

[1] R. L. McCrory, J. M. Soures, C. P. Verdon, F. J. Marshall, S. A. Letzring, S. Skupsky, T. J. Kessler, R. L. Kremens, J. P. Knauer, H. Kim, J. Delettrez, R. L. Keck, and D.K. Bradley, “Laser-Driven Implosion of Thermonuclear Fuel to 20 to 40 g cm^-3, Nature 335 (6187) 225-230 (1988).

Shown here is an image from a Nature article

High-Density Compression

March 1, 1987/in Timeline/by Rodi Keisidis

1987:

The first cryogenic target system was installed on the OMEGA chamber in support of achieving the Department of Energy (DOE) goal of compressing a cryogenic direct-drive target to a density of 100 to 200x liquid DT density. Many laser shots were taken during the summer and early fall before it was decided to suspend shots in order to carry out several system redesigns. Among the principal problems faced at that time were target vibration, unpredictable cryogenic shroud retraction, and poor DT-layer quality. The lessons learned on this first OMEGA cryogenic system helped in the future design of the much more challenging cryogenic system that was developed a decade later for LLE experiments.

Review Recognizes LLE Research

March 1, 1986/in Timeline/by Rodi Keisidis

1986:

In March, 1986 the National Academy of Sciences Review of the Department of Energy’s Inertial Confinement Fusion (ICF) Program recognized the important work being done by LLE in addressing the key aspects of ICF research. They set a goal of compressing a cryogenic direct-drive target to 100 to 200× liquid-DT density as a demonstration to justify the upgrade of the OMEGA laser to 30 kJ.

W. Happer, ed., Review of the DoE’s Inertial Confinement Fusion Program (National Academy of Sciences, Washington, DC 1986).

Image shown is a Horseshoe mount for 24-beam OMEGA cryogenic target

August 1986 cover of Scientific American

Progress in Laser Fusion

January 1, 1986/in Timeline/by Rodi Keisidis

1986:

In August 1986, the cover of Scientific American showed the diagnostics inside the OMEGA target chamber. The featured article was titled “Progress in Laser Fusion” by R. Stephen Craxton, Robert L. McCrory, and John M. Soures. The article discussed the considerable progress made in laser fusion since the ability to convert infrared lasers to the ultraviolet was demonstrated at LLE in 1979. The authors concluded that electric power generation using short-wavelength lasers would be feasible with lasers generating between 1.6 and 10 MJ per pulse with a fusion energy release 100× larger than the input laser energy.

[1] R. S. Craxton, R. L. McCrory, and J. M. Soures, “Progress in Laser Fusion,” Sci. Am. 255 (2) 68–79 (1986).

Spherical-Target Compression

April 1, 1985/in Timeline/by Rodi Keisidis

1985:

Spherical-target compression experiments demonstrated high neutron yield and high fuel density with 351-nm irradiation between 1985 and 1988.

(a) Composite of an x-ray micrograph (around E ~ 4 keV) of a high-yield target implosion and an alpha zone-plate image indicating the spatial distribution of the alpha particle products of thermonuclear burning. (b) Averaged radial profiles of the images in (a), together with LILAC postprocessor predictions of the same.

Chirped-Pulse Amplification

March 1, 1985/in Timeline/by Rodi Keisidis

1985:

A paper published in Optics Communications by Donna Strickland and Gerard Mourou of LLE describes the chirped-pulse amplification (CPA), a technique used to amplify ultrashort laser pulses to the petawatt level. This approach, developed and demonstrated at LLE, is the basis of modern ultrahigh-power lasers.

[1] D. Strickland and G. Mourou “Compression of Amplified Chirped Optical Pulses,” Opt. Commun. 56 3219-221 (1985).

OMEGA Frequency Conversion Completed

January 1, 1985/in Timeline/by Rodi Keisidis

1985:

Full conversion of the 24-beam OMEGA laser to 351-nm operation was completed on time and within budget in 1985.

Shown here is the 24-beam OMEGA firing, showing UV beams

National Laser Users Facility Program Publication

February 1, 1984/in Timeline/by Rodi Keisidis

1984:

A paper entitled “Experimental Facility for Nanosecond Time-Resolved Low Angle X-Ray Diffraction Experiments Using a Laser-Produced Plasma Source” by J. M. Forsyth and R. D. Frankel appeared in Review of Scientific Instruments. This project was one of the first to be carried out under the NLUF program.

[1] J. M. Forsyth and R. D. Frankel Experimental Facility for Nanosecond Time-Resolved, Low Angle X-Ray Diffraction Experiments Using a Laser-Produced Plasma Source Rev. Sci. Instrum. 55 (8) 1235 – 1242 (1984).