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K U Akli,
S B Hansen,
A J Kemp,
R R Freeman,
F N Beg,
D C Clark,
S D Chen,
D Hey,
S P Hatchett,
K Highbarger, [......], N Patel,
J Pasley,
C Shearer,
R B Stephens,
C Stoeckl,
M Storm,
W Theobald,
L D Van Woerkom,
R Weber,
M H Key
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ABSTRACT: The heating of solid targets irradiated by 5 x 10(20) W cm(-2), 0.8 ps, 1.05 microm wavelength laser light is studied by x-ray spectroscopy of the K-shell emission from thin layers of Ni, Mo, and V. A surface layer is heated to approximately 5 keV with an axial temperature gradient of 0.6 microm scale length. Images of Ni Ly(alpha) show the hot region has <or=25 microm diameter. These data are consistent with collisional particle-in-cell simulations using preformed plasma density profiles from hydrodynamic modeling which show that the >100 G bar light pressure compresses the preformed plasma and drives a shock into the solid, heating a thin layer.
Physical Review Letters 04/2008; 100(16):165002. · 7.37 Impact Factor
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A Mackinnon,
M Key,
K Akli,
F Beg,
R Clarke,
D Clarke,
M Chen,
H Chung,
S Chen,
R Freeman, [......],
M Storm,
K Tanaka,
M Tempo,
M Toley,
R Town,
S Wilks,
L VanWoerkom,
R Weber,
T Yabuuchi,
B Zhang
[show abstract]
[hide abstract]
ABSTRACT: Isochoric heating of inertially confined fusion plasmas by laser driven MeV electrons or protons is an area of great topical interest in the inertial confinement fusion community, particularly with respect to the fast ignition (FI) proposal to use this technique to initiate burn in a fusion capsule. Experiments designed to investigate electron isochoric heating have measured heating in two limiting cases of interest to fast ignition, small planar foils and hollow cones. Data from Cu K{alpha} fluorescence, crystal x-ray spectroscopy of Cu K shell emission, and XUV imaging at 68eV and 256 eV are used to test PIC and Hybrid PIC modeling of the interaction. Isochoric heating by focused proton beams generated at the concave inside surface of a hemi-shell and from a sub hemi-shell inside a cone have been studied with the same diagnostic methods plus imaging of proton induced K{alpha}. Conversion efficiency to protons has also been measured and modeled. Conclusions from the proton and electron heating experiments will be presented. Recent advances in modeling electron transport and innovative target designs for reducing igniter energy and increasing gain curves will also be discussed.
10/2006
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M. H. Key,
K. Akli,
F. Beg,
M. H. Chen,
H. K. Chung,
R. R. Freeman,
M. E. Foord,
J. S. Green,
P. M. Gu,
G. Gregori, [......],
R. A. Snavely,
R. B. Stephens,
C. Stoeckl,
M. Tabak,
W. Theobald,
K. Tanaka,
R. Town,
S. C. Wilks,
Y. Yabuuchi,
B. Zhang
Journal de Physique IV (Proceedings) 01/2006; 133:371. · 0.29 Impact Factor
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R R Freeman,
K Akli,
F Beg,
R Betti,
S Chen,
D J Clark,
P M Gu,
G Gregori,
S P Hatchett,
D Hey, [......],
C Ren,
R A Snavely,
R B Stephens,
C Stoeckl,
M Tabak,
R Town,
L Van Woerkom,
R Weber,
S C Wilks,
B B Zhang
[show abstract]
[hide abstract]
ABSTRACT: The Fast Ignition Program in the United States has enjoyed increased funding in various forms from the Office of Fusion Energy Sciences of the Department of Energy. The program encompasses experiments on large laser facilities at various world-wide locations, and benefits enormously from collaborations with many international scientists. The program includes exploratory work in cone-target design and implosion dynamics, high electron current transport measurements in normal density materials, development of diagnostics for heating measurements, generation of protons from shaped targets, theoretical work on high gain target designs, and extensive modeling development using PIC and hybrid codes.
Journal de Physique IV (Proceedings) 01/2006; 133:95-100. · 0.29 Impact Factor
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P K Patel,
M H Key,
A J Mackinnon,
R Berry,
M Borghesi,
D M Chambers,
H Chen,
R Clarke,
C Damian,
R Eagleton, [......],
R Shepherd,
R A Snavely,
D Steinman,
C Stoeckl,
M Storm,
W Theobald,
R Town,
R Van Maren,
S C Wilks,
B Zhang
[show abstract]
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ABSTRACT: We review a recent experimental campaign to study the interaction physics of petawatt laser pulses incident at relativistic intensities on solid targets. The campaign was performed on the 500 J sub-picosecond petawatt laser at the Rutherford Appleton Laboratory. An extensive suite of optical, x-ray, and particle diagnostics was employed to characterise the processes of laser absorption, electron generation and transport, thermal and K-alpha x-ray generation, and proton acceleration.
Plasma Physics and Controlled Fusion 11/2005; 47(12B):B833. · 2.42 Impact Factor
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S.C. Wilks,
S. Moon,
D. Ryutov,
P. Patel,
A. MacKinnon,
R. Shepherd,
B. Remington,
K. Akli,
B. Chang,
H. Chen, [......],
R. Snavely,
M. Tabak,
R. Town,
R.J. Clarke,
R. Heathcote,
D. Neely,
C. Stoeckel,
M. Storm,
W. Theobald,
J. Pasley
[show abstract]
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ABSTRACT: Summary form only given. Laboratory experiments that employ petawatt lasers are rapidly approaching parameter regimes once thought to be the exclusive domain of compact astrophysical objects. In fact, experiments and simulations of petawatt lasers impinging on solid density targets have always shown that some fraction (usually ~10-50%) of laser energy couples to hot electrons in the target, which can be in excess of 50 Joules. Up to this point, targets have usually been macroscopic foils (millimeter-sized slab targets) or large cones, with small wires at the end. In hopes of simulating conditions thought to be present in the higher atmospheres of neutron stars, we have designed and fielded reduced mass targets (RMTs) that are of order 100 mum times 100 mum times 5 mum. These targets were designed to achieve hotter material and radiation temperatures than previous macroscopic targets. Results from a recent campaign consisting of a series of RMT's on the Vulcan laser at Rutherford Appleton Laboratory (RAL) suggest that this is indeed the case. We present the results of spectroscopic measurements taken at RAL for copper RMT's tamped by 1 micron of aluminum on either side, and compare them to detailed particle-in-cell, hydro, and atomic physics computer simulations. By comparing them with identical targets, with the exception that the target sizes are increased to 400 mum times 400 mum and 1 mm times 1 mm, we find clear evidence for enhanced heating in the case of the smallest targets, where we infer nearly homogenous temperatures of over 200 eV for solid copper. Various explanations for the high temperatures will be explored, and applications of these results to EOS measurements and astrophysics will be discussed
Plasma Science, 2005. ICOPS '05. IEEE Conference Record - Abstracts. IEEE International Conference on; 07/2005
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J S Green,
K L Lancaster,
K U Akli,
C D Gregory,
F N Beg,
S N Chen,
D Clark,
R R Freeman,
S Hawkes,
C Hernandez-Gomez, [......], N Patel,
R Stephens,
M Storm,
M Tampo,
W Theobald,
L Van Woerkom,
R L Weber,
M S Wei,
N C Woolsey,
And P A Norreys
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MH Key,
K Akli,
F. Beg,
MH Chen,
HK Chung,
RR Freeman,
ME Foord,
JS Green,
P Gu,
G Gregori, [......],
RA Snavely,
RB Stephens,
C Stoeckl,
M Tabak,
W Theobald,
K Tanaka,
R Town,
SC Wilks,
T Yabuuchi,
B Zhang
[show abstract]
[hide abstract]
ABSTRACT: Isochoric heating by electrons has been measured in the two limiting cases of small area thin foils with dominant refluxing and cone-long-wire geometry with negligible refluxing in the wire. Imaging of Cu K alpha fluorescence, crystal x-ray spectroscopy of Cu K shell emission, and XUV imaging at 68eV and 256eV are discussed. Laser power on target was typically 0.5 PW in 0.7ps. Heating by focused proton beams generated at the concave inside surface of a hemi-shell and from a sub hemi-shell inside a 30 degrees cone has been studied with the same diagnostic methods plus imaging of proton induced K alpha. Conversion efficiency to protons has been measured and modeled. Conclusions from the experiments, links to theoretical understanding and relevance to fast ignition are outlined.
