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W Theobald,
C Stoeckl,
P A Jaanimagi,
P M Nilson,
M Storm,
D D Meyerhofer,
T C Sangster,
D Hey,
A J MacKinnon,
H-S Park, [......],
R B Stephens,
K U Akli,
K Highbarger,
R L Daskalova,
L Van Woerkom,
R R Freeman,
J S Green,
G Gregori,
K Lancaster,
P A Norreys
[show abstract]
[hide abstract]
ABSTRACT: A dual-channel, curved-crystal spectrograph was designed to measure time-integrated x-ray spectra in the approximately 1.5 to 2 keV range (6.2-8.2 A wavelength) from small-mass, thin-foil targets irradiated by the VULCAN petawatt laser focused up to 4x10(20) W/cm(2). The spectrograph consists of two cylindrically curved potassium-acid-phthalate crystals bent in the meridional plane to increase the spectral range by a factor of approximately 10 compared to a flat crystal. The device acquires single-shot x-ray spectra with good signal-to-background ratios in the hard x-ray background environment of petawatt laser-plasma interactions. The peak spectral energies of the aluminum He(alpha) and Ly(alpha) resonance lines were approximately 1.8 and approximately 1.0 mJ/eV sr (approximately 0.4 and 0.25 J/A sr), respectively, for 220 J, 10 ps laser irradiation.
The Review of scientific instruments 09/2009; 80(8):083501. · 1.52 Impact Factor
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M. H. Key,
J. C. Adam,
K. U. Akli,
M. Borghesi,
M. H. Chen,
R. G. Evans,
R. R. Freeman,
H. Habara,
S. P. Hatchett,
J. M. Hill, [......],
T. Phillips,
L. Romagnani, R. A. Snavely,
R. Stephens,
C. Stoeckl,
R. Town,
Y. Toyama,
B. Zhang,
M. Zepf,
P. A. Norreys
[show abstract]
[hide abstract]
ABSTRACT: An integrated experiment relevant to fast ignition. A Cu-doped deuterated polymer spherical shell target with an inserted hollow An cone is imploded by a six-beam 900-J, 1-ns laser. A 10-ps, 70-J laser pulse is focused into the cone at, the time of peak compression. The flux of high-energy electrons through the imploded material is determined from the yield of Cu K alpha fluorescence by comparison with a Monte Carlo model. The electrons are estimated to carry about 15% of the laser energy. Collisional and Ohmic heating are modeled, and Ohmic effects are shown to be relatively unimportant. An electron spectrometer shows significantly greater reduction of the transmitted electron flux than is calculated in the model. Enhanced scattering by instability-induced magnetic fields is suggested. An extension of this fluor-based technique to measurement of coupling efficiency. to the ignition hot spot in future larger-scale fast ignition experiments is outlined. (C) 2008 American Institute of Physics.
Physics of Plasmas 01/2008; 15(2). · 2.15 Impact Factor
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R. A. Snavely,
B. Zhang,
K. Akli,
Z. Chen,
R. R. Freeman,
P. Gu,
S. P. Hatchett,
D. Hey,
J. Hill,
M. H. Key, [......],
P. Patel,
R. Stephens,
M. Tampo,
K. A. Tanaka,
R. Town,
Y. Toyama,
T. Tsutsumi,
S. C. Wilks,
T. Yabuuchi,
J. Zheng
[show abstract]
[hide abstract]
ABSTRACT: The results of laser-driven proton beam focusing and heating with a high energy (170 J) short pulse are reported. Thin hemispherical aluminum shells are illuminated with the Gekko petawatt laser using 1 μm light at intensities of ∼ 3×1018 W/cm2 and measured heating of thin Al slabs. The heating pattern is inferred by imaging visible and extreme-ultraviolet light Planckian emission from the rear surface. When Al slabs 100 μm thick were placed at distances spanning the proton focus beam waist, the highest temperatures were produced at 0.94× the hemisphere radius beyond the equatorial plane. Isochoric heating temperatures reached 81 eV in 15 μm thick foils. The heating with a three-dimensional Monte Carlo model of proton transport with self-consistent heating and proton stopping in hot plasma was modeled.
Physics of Plasmas 09/2007; 14(9):092703-092703-5. · 2.15 Impact Factor
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Peimin Gu,
B. Zhang,
M. H. Key,
S. P. Hatchett,
T. Barbee,
R. R. Freeman,
K. Akli,
D. Hey,
J. A. King,
A. J. Mackinnon, R. A. Snavely,
R. B. Stephens
[show abstract]
[hide abstract]
ABSTRACT: A 68 eV extreme-ultraviolet light imaging diagnostic measures short pulse isochoric heating by electrons and protons in petawatt laser experiments. Temperatures are deduced from the absolute intensities and comparison with modeling using a radiation hydrodynamics code.
Review of Scientific Instruments 11/2006; 77(11):113101-113101-6. · 1.37 Impact Factor
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A J Mackinnon,
P K Patel,
M Borghesi,
R C Clarke,
R R Freeman,
H Habara,
S P Hatchett,
D Hey,
D G Hicks,
S Kar, [......],
K Lancaster,
D Neely,
A Nikkro,
P A Norreys,
M M Notley,
T W Phillips,
L Romagnani, R A Snavely,
R B Stephens,
R P J Town
[show abstract]
[hide abstract]
ABSTRACT: Protons accelerated by a picosecond laser pulse have been used to radiograph a 500 microm diameter capsule, imploded with 300 J of laser light in 6 symmetrically incident beams of wavelength 1.054 microm and pulse length 1 ns. Point projection proton backlighting was used to characterize the density gradients at discrete times through the implosion. Asymmetries were diagnosed both during the early and stagnation stages of the implosion. Comparison with analytic scattering theory and simple Monte Carlo simulations were consistent with a 3+/-1 g/cm3 core with diameter 85+/-10 microm. Scaling simulations show that protons>50 MeV are required to diagnose asymmetry in ignition scale conditions.
Physical Review Letters 08/2006; 97(4):045001. · 7.37 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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H. S. Park,
N. Izumi,
M. H. Key,
J. A. King,
J. A. Koch,
O. L. Landen,
P. K. Patel,
D. F. Price,
B. A. Remington,
H. F. Robey, [......],
D. M. Chambers,
R. Eagleton,
T. Goldsack,
R. J. Clarke,
R. Heathcote,
E. Giraldez,
A. Nikroo,
D. A. Steinman,
R. B. Stephens,
B. B. Zhang
Physics of Plasmas 01/2006; 13:056309. · 2.15 Impact Factor
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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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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]
[hide abstract]
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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J. A. King,
K. Akli, R. A. Snavely,
B. Zhang,
M. H. Key,
C. D. Chen,
M. Chen,
S. P. Hatchett,
J. A. Koch,
A. J. MacKinnon, [......],
R. R. Freeman,
M. Borghesi,
L. Romagnani,
M. Zepf,
T. Cowan,
R. Stephens,
K. L. Lancaster,
C. D. Murphy,
P. Norreys,
C. Stoeckl
[show abstract]
[hide abstract]
ABSTRACT: Kα radiation generated by interaction of an ultrashort (1 ps ) laser with thin (25 μ m ) Ti foils at high intensity (2×10<sup>16</sup> W / cm <sup>2</sup>) is analyzed using data from a spherical Bragg crystal imager and a single hit charge-coupled device spectrometer together with Monte Carlo simulations of Kα brightness. Laser to Kα and electron conversion efficiencies have been determined. We have also measured an effective crystal reflectivity of 3.75±2% . Comparison of imager data with data from the relatively broadband single hit spectrometer has revealed a reduction in crystal collection efficiency for high Kα yield. This is attributed to a shift in the K -shell spectrum due to Ti ionization.
The Review of scientific instruments 08/2005; · 1.52 Impact Factor
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G. Gregori,
S. B. Hansen,
R. Clarke,
R. Heathcote,
M. H. Key,
J. King,
R. I. Klein,
N. Izumi,
A. J. Mackinnon,
S. J. Moon, [......],
J. Pasley,
N. Patel,
P. K. Patel,
B. A. Remington,
D. D. Ryutov,
R. Shepherd, R. A. Snavely,
S. C. Wilks,
B. B. Zhang,
S. H. Glenzer
[show abstract]
[hide abstract]
ABSTRACT: We have measured high resolution copper Kα spectra from a picosecond high intensity laser produced plasma. By fitting the shape of the experimental spectra with a self-consistent-field model which includes all the relevant line shifts from multiply ionized atoms, we are able to infer time and spatially averaged electron temperatures (Te) and ionization state (Z) in the foil. Our results show increasing values for Te and Z when the overall mass of the target is reduced. In particular, we measure temperatures in excess of 200 eV with Z ∼ 13-14. For these conditions the ion-ion coupling constant is Γii ∼ 8-9, thus suggesting the achievement of a strongly coupled plasma regime. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
Beiträge aus der Plasmaphysik 06/2005; 45(3‐4):284 - 292.
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G Gregori,
S B Hansen,
M H Key,
J King,
A J Mackinnon,
H.-S Park,
P K Patel,
R Shepard, R A Snavely,
S C Wilks,
S H Glenzer
05/2005;
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M. Tabak,
D. S. Clark,
S. P. Hatchett,
M. H. Key,
B. F. Lasinski, R. A. Snavely,
S. C. Wilks,
R. P. J. Town,
R. Stephens,
E. M. Campbell,
R. Kodama,
K. Mima,
K. A. Tanaka,
S. Atzeni,
R. Freeman
[show abstract]
[hide abstract]
ABSTRACT: Marshall Rosenbluth’s extensive contributions included seminal analysis of the physics of the laser-plasma interaction and review and advocacy of the inertial fusion program. Over the last decade he avidly followed the efforts of many scientists around the world who have studied Fast Ignition, an alternate form of inertial fusion. In this scheme, the fuel is first compressed by a conventional inertial confinement fusion driver and then ignited by a short ( ∼ 10 ps) pulse, high-power laser. Due to technological advances, such short-pulse lasers can focus power equivalent to that produced by the hydrodynamic stagnation of conventional inertial fusion capsules. This review will discuss the ignition requirements and gain curves starting from simple models and then describe how these are modified, as more detailed physics understanding is included. The critical design issues revolve around two questions: How can the compressed fuel be efficiently assembled? And how can power from the driver be delivered efficiently to the ignition region? Schemes to shorten the distance between the critical surface where the ignitor laser energy is nominally deposited and the ignition region will de discussed. The current status of Fast Ignition research is compared with our requirements for success. Future research directions will also be outlined.
Physics of Plasmas 05/2005; 12(5):057305-057305-8. · 2.15 Impact Factor
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R. Kodama,
Y. Sentoku,
Z. L. Chen,
G. R. Kumar,
S. P. Hatchett,
Y. Toyama,
T. E. Cowan,
R. R Freeman,
J. Fuchs,
Y. Izawa, [......],
T. Matsuoka,
H. Nakamura,
M. Nakatsutsumi,
P. A. Norreys,
T. Norimatsu, R. A. Snavely,
R. B. Stephens,
M. Tampo,
K. A. Tanaka,
T. Yabuuchi
Nature 12/2004; 432(7020):1005-1008. · 36.28 Impact Factor
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R B Stephens, R A Snavely,
Y Aglitskiy,
F Amiranoff,
C Andersen,
D Batani,
S D Baton,
T Cowan,
R R Freeman,
T Hall, [......],
M Koenig,
A J MacKinnon,
K L Lancaster,
E Martinolli,
P Norreys,
E Perelli-Cippo,
M Rabec Le Gloahec,
C Rousseaux,
J J Santos,
F Scianitti
[show abstract]
[hide abstract]
ABSTRACT: Electron transport within solid targets, irradiated by a high-intensity short-pulse laser, has been measured by imaging K(alpha) radiation from high- Z layers (Cu, Ti) buried in low- Z (CH, Al) foils. Although the laser spot is approximately 10 microm [full width at half maximum (FWHM)], the electron beam spreads to > or =70 microm FWHM within <20 microm of penetration into an Al target then, at depths >100 microm, diverges with a 40 degree spreading angle. Monte Carlo and analytic models are compared to our data. We find that a Monte Carlo model with a heuristic model for the electron injection gives a reasonable fit with our data.
Physical Review E 07/2004; 69(6 Pt 2):066414. · 2.26 Impact Factor
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R A Snavely,
P Gu,
J King,
D Hey,
K Akli,
B B Zhang,
R Freeman,
S Hatchett,
M H Key,
J Koch, [......],
Z Chen,
T Yabuuchi,
T Kurahashi,
T Sato,
K Adumi,
Y Toyama,
J Zheng,
R Kodama,
K A Tanaka,
T Yamanaka
[show abstract]
[hide abstract]
ABSTRACT: It has recently been demonstrated that femtosecond-laser generated proton beams may be focused. These protons, following expansion of the Debye sheath, emit off the inner concave surface of hemispherical shell targets irradiated at their outer convex pole. The sheath normal expansion produces a rapidly converging proton beam. Such focused proton beams provide a new and powerful means to achieve isochoric heating to high temperatures. They are potentially important for measuring the equation of state of materials at high energy density and may provide an alternative route to fast ignition. We present the first results of proton focusing and heating experiments performed at the Petawatt power level at the Gekko XII Laser Facility at ILE Osaka Japan. Solid density Aluminum slabs are placed in the proton focal region at various lengths. The degree of proton focusing is measured via XUV imaging of Planckian emission of the heated zone. Simultaneous with the XUV measurement a streaked optical imaging technique, HISAK, gave temporal optical emission images of the focal region. Results indicate excellent coupling between the laser-proton conversion and subsequent heating.
08/2003
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R A Snavely,
J King,
R R Freeman,
S Hatchett,
M H Key,
J Koch,
A B Langdon,
B Lasinsky,
A MacKinnon,
S Wilks,
R Stephens
[show abstract]
[hide abstract]
ABSTRACT: The transport of intense relativistic beams in solid density plasma presently is actively being studied in laser laboratories around the world. The correct understanding of the transport enables further application of fast laser driven electrons to a host of interesting uses. Advanced x-ray sources, proton and ion beam generation and plasma heating in fast ignitor fusion all are owed their eventual utility to this transport. We report on measurements of relativistic transport over the whole of the transport region, via analysis of x-ray emission. Our experiments cover laser powers from Terawatt to Petawatt. Advances in transverse imaging of fluorescent k-alpha x-rays generated along the electron beam path are used to diagnose the electron emission. Additionally the spatial pattern of Bremsstrahlung x-rays provides clues into the physics of electron transport in above Alfven current limit beams. Issues regarding the electron distribution function will be discussed in light of possible electron transport anomalies. The initial experiments performed on the Nova Petawatt Laser System were those associated with determining the nature of the electrons and x-rays in this relativistic regime especially those useful for advanced radiography sources suitable for diagnostic use in dense high-Z dynamic processes or as the driver of a relativistic electron source in the Fast-Ignitor Inertial Confinement fusion concept. The development of very large arrays of thermoluminescent detectors is detailed along with their response. The characteristic pattern of x-rays and their intensity is found from detailed analysis of the TLD detector array data. Peak intensities as high as 2 Rads at 1 meter were measured with these shielded TLD arrays. An average energy yield of x-rays of 11 Joules indicates a very large fraction of 45-55% of the laser energy is absorbed into relativistic electrons. The pattern of x-ray distribution lends insight to the initial relativistic electron distribution function and subsequent transport inside solid density material. A theoretical-computational model (MPK) combining laser focal spot data with ponderomotive kinematics with Monte Carlo collisional transport is developed here, and is presented which associates the laser interaction to the observed x-ray data. There is good agreement between the MPK model and data exhibiting ponderomotive like x-rays is found. Additional agreement is had in comparison to recent electron transport experiment utilizing Cu fluorescence to map the electron flow.
08/2003
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M. H. Key,
Y. Aglitskiy,
F. Amiranoff,
C. Andersen,
D. Batani,
S. Baton,
T. E. Cowan,
N. Fisch,
R. R. Freeman,
L. Gremillet, [......],
P. Norreys,
P. B. Parks,
E. Perelli-Cippo,
M. Rabec Le Gloahec,
M. N. Rosenbluth,
C. Rousseaux,
J. J. Santos,
F. Scianitti, R. A. Snavely,
R. B. Stephens
IFSA 2002. 01/2002;
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M Roth,
T E Cowan,
M H Key,
S P Hatchett,
C Brown,
W Fountain,
J Johnson,
D M Pennington, R A Snavely,
S C Wilks,
K Yasuike,
H Ruhl,
F Pegoraro,
S V Bulanov,
E M Campbell,
M D Perry,
H Powell
[show abstract]
[hide abstract]
ABSTRACT: The concept of fast ignition with inertial confinement fusion (ICF) is a way to reduce the energy required for ignition and burn and to maximize the gain produced by a single implosion. Based on recent experimental findings at the PETAWATT laser at Lawrence Livermore National Laboratory, an intense proton beam to achieve fast ignition is proposed. It is produced by direct laser acceleration and focused onto the pellet from the rear side of an irradiated target and can be integrated into a hohlraum for indirect drive ICF.
Physical Review Letters 02/2001; 86(3):436-9. · 7.37 Impact Factor
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[show abstract]
[hide abstract]
ABSTRACT: Characterization of hot electron production from an ultraintense laser–solid target plasma interaction by using a buried molybdenum K-shell fluor layer technique has been reported. Laser energy was typically 400 J and its intensity was from 2×1018 up to 3×1020 W cm−2 at 20 TW to 1 PW laser power by changing pulse duration from 20 ps down to 0.5 ps. X-ray background noise level was significantly greater, i.e., gamma flash, in the shorter pulse experiments. Data analysis procedures for the experiments were developed. The conversion efficiency from the laser energy into the energy, carried by hot electrons, has been estimated to be ∼50% at 3×1020 W cm−2 laser intensity, higher than ∼18% at 1019 W cm−2 and ∼12% at 2×1018 W cm−2 intensity. © 2001 American Institute of Physics.
Review of Scientific Instruments 12/2000; 72(1):1236-1240. · 1.37 Impact Factor
