skip to main content
OSTI.GOV title logo U.S. Department of Energy
Office of Scientific and Technical Information

Title: Early-time measurements of laser-plasma conditions in OMEGA-Upgrade ICF Targets. Final report, April 1, 1997--March 31, 1998

Abstract

Under this FY-97 NLUF grant, we primarily carried out spectral line and continuum diagnostics at early times and in the coronal region of the plasma using our flat-field grazing-incidence spectrograph, improved to incorporate time resolution at wavelengths extending below the carbon K-absorption edge using a gated microchannel plate detector. These experiments were carried out on the OMEGA facility. Fifty-nine beams were focused onto the target, providing nominally 18 kJ of energy in a 1 ns pulse for an irradiance of {approximately}2{times}10{sup 14}/cm{sup 2}. Some beam smoothing, provided by spectral dispersion, was used, but may not have been particularly effective alone, i.e., without the presence of distributed phase plates in the beams. The plastic microballoon targets were nominally 900 {mu}m in diameter with 10- and 20-{mu}m thick walls, and were filled with neon to a pressure of 10 atm. Overcoatings of Mg and Al in thicknesses ranging from 0.2 to 4 {mu}m were applied. A 1-{mu}m thick layer of CH was added in some early shots to reduce the rate of expansion of the metallic coatings. In the extreme ultraviolet (euv) spectral region, we observed n=3 to n=2 emissions from Li-, He- and H-like ions from the Mg and Al coatings.more » We also obtained evidence confirming our previously-published laser-field-induced satellites lines at 53.1 {Angstrom} and 62.8 {Angstrom}, apparently at the peak of the Gaussian drive pulse. Both the Mg-line and the continuum euv emissions are high during the radial collapse. The metallic coating materials appear to be in place to some degree during the compression phase, i.e., are not all blown away as coronal plasma at earlier times as modeled. This also is apparent in the Al Lyman-{alpha} x-ray measurements before and after compression. Here, however, higher line opacity made it difficult to track the resonance lines through the compression phase. This illustrates the importance of euv measurements of less opaque lines at high densities.« less

Authors:
;
Publication Date:
Research Org.:
Maryland Univ., College Park, MD (United States)
Sponsoring Org.:
USDOE, Washington, DC (United States)
OSTI Identifier:
594434
Report Number(s):
DOE/SF/21271-2
ON: DE98004774; TRN: 98:001908
DOE Contract Number:
FG03-97SF21271
Resource Type:
Technical Report
Resource Relation:
Other Information: PBD: 4 Apr 1998
Country of Publication:
United States
Language:
English
Subject:
70 PLASMA PHYSICS AND FUSION; PROGRESS REPORT; LASER-PRODUCED PLASMA; LASER TARGETS; OMEGA FACILITY; X-RAY SPECTROSCOPY; TIME MEASUREMENT

Citation Formats

Griem, H.R., and Elton, R.C. Early-time measurements of laser-plasma conditions in OMEGA-Upgrade ICF Targets. Final report, April 1, 1997--March 31, 1998. United States: N. p., 1998. Web. doi:10.2172/594434.
Copy to clipboard
Griem, H.R., & Elton, R.C. Early-time measurements of laser-plasma conditions in OMEGA-Upgrade ICF Targets. Final report, April 1, 1997--March 31, 1998. United States. doi:10.2172/594434.
Copy to clipboard
Griem, H.R., and Elton, R.C. Sat . "Early-time measurements of laser-plasma conditions in OMEGA-Upgrade ICF Targets. Final report, April 1, 1997--March 31, 1998". United States. doi:10.2172/594434. https://www.osti.gov/servlets/purl/594434.
Copy to clipboard
@article{osti_594434,
title = {Early-time measurements of laser-plasma conditions in OMEGA-Upgrade ICF Targets. Final report, April 1, 1997--March 31, 1998},
author = {Griem, H.R. and Elton, R.C.},
abstractNote = {Under this FY-97 NLUF grant, we primarily carried out spectral line and continuum diagnostics at early times and in the coronal region of the plasma using our flat-field grazing-incidence spectrograph, improved to incorporate time resolution at wavelengths extending below the carbon K-absorption edge using a gated microchannel plate detector. These experiments were carried out on the OMEGA facility. Fifty-nine beams were focused onto the target, providing nominally 18 kJ of energy in a 1 ns pulse for an irradiance of {approximately}2{times}10{sup 14}/cm{sup 2}. Some beam smoothing, provided by spectral dispersion, was used, but may not have been particularly effective alone, i.e., without the presence of distributed phase plates in the beams. The plastic microballoon targets were nominally 900 {mu}m in diameter with 10- and 20-{mu}m thick walls, and were filled with neon to a pressure of 10 atm. Overcoatings of Mg and Al in thicknesses ranging from 0.2 to 4 {mu}m were applied. A 1-{mu}m thick layer of CH was added in some early shots to reduce the rate of expansion of the metallic coatings. In the extreme ultraviolet (euv) spectral region, we observed n=3 to n=2 emissions from Li-, He- and H-like ions from the Mg and Al coatings. We also obtained evidence confirming our previously-published laser-field-induced satellites lines at 53.1 {Angstrom} and 62.8 {Angstrom}, apparently at the peak of the Gaussian drive pulse. Both the Mg-line and the continuum euv emissions are high during the radial collapse. The metallic coating materials appear to be in place to some degree during the compression phase, i.e., are not all blown away as coronal plasma at earlier times as modeled. This also is apparent in the Al Lyman-{alpha} x-ray measurements before and after compression. Here, however, higher line opacity made it difficult to track the resonance lines through the compression phase. This illustrates the importance of euv measurements of less opaque lines at high densities.},
doi = {10.2172/594434},
journal = {},
number = ,
volume = ,
place = {United States},
year = {Sat Apr 04 00:00:00 EST 1998},
month = {Sat Apr 04 00:00:00 EST 1998}
}
Copy to clipboard
Technical Report:
View Technical Report (0.93 MB)
DOI:  10.2172/594434
Save / Share:
Export Metadata
Save to My Library
You must Sign In or Create an Account in order to save documents to your library.

  • ;
    Since arrival of FY-98 funding under this grant in December, we have been preparing for our first series of experiments under this grant at the University of Rochester Laboratory for Laser Energetics (LLE) on the Omega laser facility, now scheduled the week beginning May 4, 1998. We will again be fielding our flat-field, grazing-incidence extreme-ultraviolet (euv) spectrograph with a four-channel gated-stripline microchannel plate (MCP) detector, which is mounted on the outside of the vacuum chamber approximately 60 inches from the center. In addition, we will be using for the first time our newly constructed flat field spectrograph covering the spectralmore » range of 30-250 {angstrom} (hv = 50-400 eV), designed to fit into a Ten Inch Manipulator (TIM). As such, it can be located closer to the central target position, with an expected enhancement in sensitivity of at least a factor-of-ten. It is the preparation of this instrument that mainly has occupied our attention so far in this grant period and discussed in this report.« less

  • ;
    All of the experimental results from OMEGA shots described here are from CY-1998 experiments under an (extended) FY-98 grant. This research involves fielding at LLE their two flat-field euv spectrographs in the 30--250 {angstrom} range, mainly utilizing on one o them a gated stripline microchannel plate as a time-resolved detector, with photographic recording. The experimental layout for the 1998 experiments is shown. During the week beginning May 3, 1998, the authors obtained 24 data shots over 4 days, and fielded both the time-gated extreme ultraviolet (euv) spectrograph mounted external to the target chamber, as well as their newly-constructed TIM-mounted euvmore » spectrograph mounted closer to the target with time-integrated photographic recording on a trial basis. They also had available the LLE/LLNL streak x-ray spectrograph and x-ray imaging cameras. In this series, the first two shots appeared from the x-ray streak spectra to be normal in the sense that the spectral line emissions from the two coatings sequenced beginning with magnesium followed by aluminum as the coatings were vaporized. Unfortunately, on the following shots in this campaign it became increasingly apparent that conditions had changed radically, and later analyses showed that x-ray spectra lines from the deep aluminum undercoating appeared initially along with weak magnesium lines, indicating a premature vaporization of the magnesium heavier top layer. The second campaign in 1998 occurred during the week beginning October 18, 1998 and consisted of 21 data shots over two extended (12-hour) days following setup. For this series the authors again used their externally-mounted euv spectrography with time resolution and the x-ray streak spectrograph and imaging cameras. Much to their relief, it was immediately evident from the x-ray streak spectra obtained that significant ablation of the magnesium coatings by a (presumed) prepulse was not present, as it had been in the May campaign.« less

  • ; ;
    Beginning in January 1997 (following arrival of the FY-97 funding) we have been preparing for our first series of experiments under this grant at the University of Rochester Laboratory for Laser Energetics (LLE) on the Omega Upgrade laser facility, now scheduled to commence June 2, 1997. For these experiments we have purchased (just arrived) a four-channel gated-stripline microchannel plate (MCP) detector to be coupled to our soft x-ray flat-field grazing incidence spectrograph used previously at LLE. This will permit time-resolved `snapshots` of the complete spectra with a resolution to times as short as 180 ps per strip. An advantage ofmore » this technique over the streak camera used previously is the lack of any carbon absorbers such as in the thin plastic cathode required for the streak camera. This eliminates absorption in the 30-44 {angstrom} spectral region in which we are interested for intermediate-Z target materials such as Mg, Al and Si. An auxiliary turbomolecular-drag pump has also been installed in order to obtain the necessary vacuum for optimum MCP operation.« less

  • ; ;
    Under this FY-96 NLUF program, the authors primarily carried out an initial search for satellite lines to forbidden transitions for localized laser-induced electric field measurements, using their flat-field grazing incidence spectrograph on the OMEGA-Upgrade facility at the University of Rochester Laboratory for Laser Energetics (LLE). In a second 1996 series of experiments carried out in September the authors were able to complete 19 shots using all 60 beams and spherical targets consisting of neon-filled microballoons with coatings of aluminum, magnesium and sodium fluoride, sometimes overcoated with a plastic (CH) layer. With cooperation from Dr. Paul Jaanimagi of LLE, they succeededmore » in adding a LLE streak camera for time resolution. The electric fields that they measured corresponded to laser irradiances comparable to those applied, accounting for some losses in the plasma. The details with figures are included in an attached preprint of a paper recently accepted for publication in the Journal of Quantitative Spectroscopy and Radiative Transfer (JQSRT) as part of the Proceedings of the November 1996 Conference on Radiative Properties of Hot Dense Matter at which the results were presented. They were also presented at the 1996 American Physical Society Division of Plasma Physics Conference in Denver in November 1996.« less

  • ;
    Since arrival of FY-99 funding in December, the authors have been preparing for the first series of experiments under this grant on the OMEGA laser facility, which just took place (for one day) on April 27, 1999. The campaign was successful and results will be included in the next progress report following analyses. For the first time, they fielded their Ten Inch Manipulator (TIM-) mounted flat-field, grazing-incidence extreme-ultraviolet (euv) spectrograph with a four-channel gated-stripline microchannel plate (MCP) detector. This spectrograph covers the spectral range of 30--250 {angstrom} (hv = 50--400 eV). As in a previous campaign of May 1998, wheremore » the authors used this instrument with time-integrated photographic recording, the spectrograph reached closer to the target than did the previous version mounted on the chamber wall; such that the sensitivity increased by at least a factor-of-10 for viewing weak spectral features. The analysis during this reporting period of the euv spectroscopic results from the October 1998 NLUF/OMEGA campaign of Mg X, XI and XII spectra from n = 3 to n = 2 transitions are shown in Fig. 1 versus time. The data plotted represent a composite between the three most sensitive striplines, delayed relative to each other, for a number of shots. The intended emphasis was on the early portion of the event while the laser intensity is rising to a peak. This measured euv history agrees with that from the x-ray streak spectrographic data shown in Fig. 2 from the same campaign, i.e., the peak period of emission being in the first 1.5 ns.« less