Spall strength was measured as a function of composition and microstructure in three Al materials: a high-purity Al (AlHP), a commercial-purity Al (AA1100) and an alloy of Al containing 3 wt.% Mg (Al-3Mg). The Al HP and AA1100 materials were tested as single-crystal sheets, and the Al-3Mg alloy was tested as polycrystalline sheets having a variety of controlled grain sizes. A high-intensity laser produced shock loadings to create tensile strain rates ranging from 2 x 10(6) s(-1) to 5 x 10(6) s(-1), which caused spall fracture. Crystallographic orientation, relative to the direction of shock propagation, does not discernibly affect spall strength in the Al-HP material. Intermetallic particles, associated with impurity elements, initiate microstructural damage during tensile shock loading and reduce spall strength of the AA1100 material below that of the Al-HP material. The spall strength of the Al-3Mg is lowest among the three materials, and this is a result of the decreased ductility during spall fracture caused by the Mg solid-solution alloying addition. Grain size affects fracture character of the Al-3Mg material, but does not discernibly affect spall strength; the fraction of ductile transgranular fracture, versus brittle intergranular fracture, increases with grain size. (C) 2011 Elsevier B.V. All rights reserved.

Explosions of large Xe clusters (< Ni > similar to 11 000) irradiated by femtosecond pulses of 850 eV x-ray photons focused to an intensity of up to 1017 W/cm(2) from the Linac Coherent Light Source were investigated experimentally. Measurements of ion charge-state distributions and energy spectra exhibit strong evidence for the formation of a Xe nanoplasma in the intense x-ray pulse. This x-ray produced Xe nanoplasma is accompanied by a three-body recombination and hydrodynamic expansion. These experimental results appear to be consistent with a model in which a spherically exploding nanoplasma is formed inside the Xe cluster and where the plasma temperature is determined by photoionization heating.

We report electron acceleration to 1.25 GeV by petawatt-laser-driven wakefield acceleration at plasma density 5x10(17) cm(-3). Electron beams are dark-current-free, quasi-monoenergetic, highly collimated (<1mrad divergence), contain tens of pC and have excellent pointing stability. (C)2012 Optical Society of America

Magnetized collimated plasma jets are created in the laboratory to extend our understanding of plasma jet acceleration and collimation mechanisms with particular connection to astrophysical jets. In this study, plasma collimated jets are formed from supersonic unmagnetized flows, mimicking a stellar wind, subject to currents and magnetohydrodynamic forces. It is found that an external poloidal magnetic field, like the ones found anchored to accretion disks, is essential to stabilize the jets against current-driven instabilities. The maximum jet length before instabilities develop is proportional to the field strength and the length threshold agrees well with Kruskal-Shafranov theory. The plasma evolution is modeled qualitatively using MHD theory of current-carrying flux tubes showing that jet acceleration and collimation arise as a result of electromagnetic forces. (C) 2012 American Institute of Physics. [doi: 10.1063/1.3671953]

Electron self-injection into a laser-plasma accelerator (LPA) driven by the Texas Petawatt (TPW) laser is reported at plasma densities 1.7 - 6.2 x 10(17) cm(-3). Energy and charge of the electron beam, ranging from 0.5 GeV to 2 GeV and tens to hundreds of pC, respectively, depended strongly on laser beam quality and plasma density. Angular beam divergence was consistently around 0.5 mrad (FWHM), while shot-to-shot pointing fluctuations were limited to +/- 1.4 mrad rms. Betatron x-rays with tens of keV photon energy are also clearly observed.

We report on the first successful demonstration of selective deuteron acceleration by the target normal sheath acceleration mechanism in which the normally overwhelming proton and carbon ion contaminant signals are suppressed by orders of magnitude relative to the deuteron signal. The deuterium ions originated from a layer of heavy ice that was deposited on to the rear surface of a 500 nm thick membrane of Si3N4 and Al. Our data show that the measured spectrum of ions produced by heavy ice targets is comprised of similar to 99% deuterium ions. With a laser pulse of approximately 0.5 J, 120 fs duration, and similar to 5 x 10(18) Wcm(-2) mean intensity, the maximum recorded deuterium ion energy and yield normal to the target rear surface were 3.5 MeV and 1.2 x 10(12)sr(-1), respectively. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.3695061]

Laser acceleration of hot electrons and their transport through 12-32 mu m thick Ti foils was explored experimentally using two complementary diagnostics, a bent crystal imaging the Ti K-alpha emission and optical imaging of the coherent transition radiation (CTR) produced by the exit of the hot electrons from the foil. The spatial extent of the hot electron production measured by these two diagnostics is dramatically different. Electrons producing CTR emerge in a spot of less than 7 mu m and appear to maintain a high degree of collimation during transport through the foil while electrons that produce Ka emission appear to diverge to sizes of 50-100 mu m as viewed from the back surface of the foil. These results indicate that there is a large difference in the transport of the highest energy electrons contributing to CTR signal as compared with the bulk of the hot electron population generating K-alpha signal. (C) 2011 Elsevier B.V. All rights reserved.

We present a novel way of determining the plasma temperature in a laser-cluster fusion experiment on the Texas Petawatt laser, which uses the ratio of the 2.45 MeV neutron and 14.7 MeV proton yields.

The Texas Petawatt Laser is operational with experimental campaigns executed in both F/40 and F3 target chambers. Recent improvements have resulted in intensities of >2x10(21) W/cm(2) on target. Experimental highlights include, accelerated electron energies of >2 GeV, DD fusion ion temperatures >25 keV and isochorically heated solids to 10-50 eV.

Three types of neutron detectors (plastic scintillation detectors, indium activation detectors, and CR-39 track detectors) were calibrated for the measurement of 2.45 MeV DD fusion neutron yields from the deuterium cluster fusion experiment on the Texas Petawatt Laser. A Cf-252 neutron source and 2.45 MeV fusion neutrons generated from laser-cluster interaction were used as neutron sources. The scintillation detectors were calibrated such that they can detect up to 10(8) DD fusion neutrons per shot in current mode under high electromagnetic pulse environments. Indium activation detectors successfully measured neutron yields as low as 10(4) per shot and up to 10(11) neutrons. The use of a Cf-252 neutron source allowed cross calibration of CR-39 and indium activation detectors at high neutron yields (similar to 10(11)). The CR-39 detectors provided consistent measurements of the total neutron yield of Cf-252 when a modified detection efficiency of 4.6x10(-4) was used. The combined use of all three detectors allowed for a detection range of 10(4) to 10(11) neutrons per shot. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4729121]

We report on nanosecond resolution lattice measurements of shock-compressed Mg in the hcp and bcc phases between 12 and 45 GPa. X-ray diffraction signals consistent with a compressed bcc lattice were captured above a shock pressure of 26.2 +/- 1.3 GPa. Our results are in agreement with the phase boundary calculated by Moriarty and Althoff using the generalized pseudopotential theory in the pressure and temperature region intersected by the principal shock Hugoniot.

We report production of a self-injected, collimated (8 mrad divergence), 600 pC bunch of electrons with energies up to 350 MeV from a petawatt laser-driven plasma accelerator in a plasma of electron density n(e) = 10(17)cm(-3), an order of magnitude lower than previous self-injected laser-plasma accelerators. The energy of the focused drive laser pulse (150J, 150 fs) was distributed over several hot spots. Simulations show that these hot spots remained independent over a 5 cm interaction length, and produced weakly nonlinear plasma wakes without bubble formation capable of accelerating pre-heated (similar to 1 MeV) plasma electrons up to the observed energies. The required pre-heating is attributed tentatively to pre-pulse interactions with the plasma.

We report on the measurement and computer simulation of the divergence of fast electrons generated in an ultraintense laser-plasma interaction (LPI) and the subsequent propagation in a nonrefluxing target. We show that, at I lambda(2) of 10(20) Wcm(-2) mu m(2), the time-integrated electron beam full divergence angle is (60 +/- 5)degrees. However, our time-resolved 2D particle-in-cell simulations show the initial beam divergence to be much smaller (<= 30 degrees). Our simulations show the divergence to monotonically increase with time, reaching a final value of (68 +/- 7)degrees after the passage of the laser pulse, consistent with the experimental time-integrated measurements. By revealing the time-dependent nature of the LPI, we find that a substantial fraction of the laser energy (similar to 7%) is transported up to 100 mu m with a divergence of 32 degrees.