Bulletin of the American Physical Society
54th Annual Meeting of the APS Division of Plasma Physics
Volume 57, Number 12
Monday–Friday, October 29–November 2 2012; Providence, Rhode Island
Session JO5: Intense Laser-Plasma Interactions: Experiment |
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Chair: Louise Willingale, University of Michigan Room: 552AB |
Tuesday, October 30, 2012 2:00PM - 2:12PM |
JO5.00001: Tracking Intense Flows of Energy Inside OMEGA EP Laser-Irradiated Metal Targets P.M. Nilson, J.R. Davies, A.A. Solodov, R. Betti, D.D. Meyerhofer, G. Fiksel, C. Stoeckl, P.A. Jaanimagi, C. Mileham, W. Theobald, J.F. Myatt, D.H. Froula Generating intense flows of energy inside matter is essential for a wide range of basic and applied high-energy-density science. A new, monochromatic, streaked x-ray crystal imager has been developed and deployed on the OMEGA EP laser to study collisional ionization-wave dynamics driven by hot electrons inside a metal. Spatial, spectral, and temporal resolution is obtained by coupling a spherically bent crystal imager to a 2-ps-resolution x-ray streak camera. The instrument measures the spatial location of the Cu K$_{\alpha }$ emission across a 1-D lineout of a thin-foil target as a function of time with a spatial resolution of $\sim $10 \textit{$\mu $}m, tracking the hot-electron flow through the background plasma. The performance of and initial results from this unique diagnostic will be presented. This work was supported by the U.S. Department of Energy Office of Inertial Confinement Fusion under Cooperative Agreement No. DE-FC52-08NA28302. [Preview Abstract] |
Tuesday, October 30, 2012 2:12PM - 2:24PM |
JO5.00002: Demonstration of short pulse laser heating of solid targets to temperatures of 600eV at depths exceeding 30$\mu $m using the Orion high power laser L.M.R. Hobbs, D.J. Hoarty, P. Allan, C.R.D. Brown, M.P. Hill, S.F. James, R. Shepherd, K.L. Lancaster, R.J. Gray, E. Wagenaars, R.J. Dance, A.K. Rossall, O. Culfa, N.C. Woolsey The recently completed Orion laser at AWE in the UK has the capability of delivering a petaWatt short pulse at 1.06$\mu $m in two of its twelve laser beams. In the experiments described one of the short pulse beams was converted to 2nd harmonic at sub-aperture delivering 3x10$^{20}$W/cm$^{2}$ (100J of 0.53$\mu $m light in 0.5ps) onto plastic foils (parylene N) with embedded tracer layers of aluminium. The target heating profile was recorded on a shot by shot basis by changing the depth of the plastic overcoat between the laser and the buried aluminium layer and recording the aluminium K-shell emission spectra. These spectra were then compared to the FLY atomic kinetics and line-shape code to infer the conditions in the target. Temperatures of 600eV were recorded through a plastic depth in excess of 30$\mu $m. In contrast to this similar experiments conducted with the Orion short pulse beam operating at wavelength 1.06$\mu $m at energy of 500J ($\sim $10$^{21}$W/cm$^{2})$ produced heating through only 5$\mu $m of plastic. The importance of the improved pulse contrast in 2nd harmonic operation in solid target heating is clear from these results. The data are also compared to results from similar experiments conducted on the VULCAN petaWatt laser using 1.06$\mu $m light but with improved pulse contrast. [Preview Abstract] |
Tuesday, October 30, 2012 2:24PM - 2:36PM |
JO5.00003: Specular reflectivity in high contrast relativistic laser-plasma interactions G. Elijah Kemp, Anthony Link, Robert Fedosejevs, Richard R. Freeman, Farhat N. Beg, Hal Friesen, Drew P. Higginson, Mike H. Key, Harry S. McLean, Prav Patel, Yuan Ping, Douglass W. Schumacher, Richard B. Stephens, Henry F. Tiedje, Ying Y. Tsui We describe a study of the relativistic electron source generated at both under-dense and over-dense plasma interfaces with relativistic laser pulses. The experiment was performed on Titan at the Jupiter Laser Facility at LLNL using planar targets with high contrast 527 nm wavelength laser pulses (created using second harmonic generation from the fundamental) with controllable additional injected pre-pulse energy. We use specularly reflected pulse properties to compare the experimental results with 2D3v Cartesian particle-in-cell simulations (using the hybrid code LSP) to infer interface effects on the relativistic electron generation. [Preview Abstract] |
Tuesday, October 30, 2012 2:36PM - 2:48PM |
JO5.00004: Commissioning of the Orion Laser system Steven James, Colin Brown, David Drew, Stuart Duffield, Stephen Elsemere, Jim Fyrth, Mark Girling, Edward Gumbrell, Matthew Hill, David Hillier, Nicholas Hopps, Michael Norman, Kevin Oades, James Palmer, Stefan Parker, Paul Treadwell, David Winter, David Hoarty We present data collected in a recent series of shots taken to commission the Orion laser system. Ten long pulse (LP, nanosecond pulse length) and two short pulse (SP, picosecond pulse length) laser beams were fired onto a series of metal and plastic foils and data recorded. X-ray images of the laser plasma interaction show LP spot sizes of less than 100$\mu $m with $>$400J of 351nm on target, consistent with wavefront measurements. Picosecond pulses operating at powers of 500TW were used to generate ion beams with large numbers of energetic (multi-ten's of MeV) protons, indicating a high focussed intensity and energetic electron acceleration. Thick-target hard X-ray dosimetry measurements were made to prove the effectiveness of the shielding. An X-ray streak camera was used to synchronise all twelve beams to within +/-50ps of each other, and all twelve beams were fired simultaneously onto a target. [Preview Abstract] |
Tuesday, October 30, 2012 2:48PM - 3:00PM |
JO5.00005: Generation of relativistic ions, electrons and positrons in high-intensity short-pulse laser-solid interactions Matthew Hill, Peter Allan, Colin Brown, Lauren Hobbs, Steven James, Kevin Oades, David Hoarty, Hui Chen The newly-commissioned Orion laser facility at AWE Aldermaston can deliver intense ($10^{21}$~W/cm$^{2}$), short (0.6~ps) laser pulses at $1\omega$ (1~$\mu$ m) and 3$\times10^{20}$~W/cm$^{2}$ at $2\omega$ with pulse contrasts of $10^{7}$ and $10^{13}$, respectively, in addition to ten $3\omega$, 500~J long-pulse ($\sim$ns) beams. All can be delivered to target synchronized to $\sim20$~ps. We report on the production and characterization of multi-MeV protons, ions, positrons and electrons at the Orion facility using 500~J, 0.6~ps, $1\omega$ pulses and 100~J, 0.6~ps, $2\omega$ pulses onto both thin (20~$\mu$ m) and thick (1~mm) gold targets. Laser intensities were scanned from $10^{19}$ to $10^{21}$~W/cm$^{2}$ by altering pulse energy and length while maintaining a consistent focal spot size of 10~$\mu$. Particle energies were recorded by use of a magnetic and a Thomson spectrometer, with X-ray emissions imaged using a time-integrating pinhole camera in addition to time-integrating crystal spectrometers. The implications for future experiments such as investigations into electron transport mechanisms and proton heating are briefly discussed. [Preview Abstract] |
Tuesday, October 30, 2012 3:00PM - 3:12PM |
JO5.00006: First electron-positron pair experiments using the Osaka LFEX laser Hui Chen, M. Nakai, Y. Sentoku, Y. Arikawa, H. Azechi, P. Beiersdorfer, S. Fujioka, C. Keane, S. Kojima, W. Goldstein, T. Morita, T. Nagai, H. Nishimura, T. Ozaki, J. Park, Y. Sakawa, H. Takabe, G.J. Williams, Z. Zhang The first laser driven electron-positron experiment using the high power LFEX laser at the Osaka University was performed by a collaborative group from LLNL and ILE. Together with high energy electrons (T$_{hot}\sim $10 MeV), relativistic positrons ($\sim $10 MeV) were observed from 1 kJ shots with laser intensity at about 10$^{20}$ W/cm$^2$ on 1 mm thick gold target. Electron accelerations in plasmas with density below critical were shown to play an important role in producing very high energy ($>$20 MeV) electrons, while the number of relatively low energy electrons ($\sim $10 MeV) appeared to be crucial to the total number of pairs produced. Detailed experiment results and simulations will be presented in this talk (by Dr. M. Nakai). [Preview Abstract] |
Tuesday, October 30, 2012 3:12PM - 3:24PM |
JO5.00007: Understanding laser-solid interactions at ultra-high intensities C.D. Murphy, R.J. Gray, D.C. Carroll, D.A. Maclellan, H. Powell, G.G. Scott, C.P. Ridgers, C.S. Brady, D. Neely, J.S. Green, N. Booth, P. McKenna The interaction of matter with lasers is a subject which has progressed rapidly over the last two decades as higher intensity lasers have opened the door to nonlinear and then relativistic interactions such that applications in ion acceleration and x-ray backlighting sources have become a clear possibility. Until recently, lasers capable of reaching the highest intensities ($\sim 10^{21} \rm{Wcm}^{-2}$) have been glass-based systems with a low shot rate making detailed studies prohibitively time consuming. The development of petawatt-class Ti:Sapphire lasers such as Astra Gemini at STFC - Rutherford Appleton Laboratory, has made the systematic studies required to understand such interaction physics feasible. One such experiment on the Astra Gemini laser will be presented. The photon and particle diagnostics used will be explained and their results presented. [Preview Abstract] |
Tuesday, October 30, 2012 3:24PM - 3:36PM |
JO5.00008: Multi-pulse laser drive to achieve higher laser-proton conversion efficiencies James Green, Ceri Brenner, Graeme Scott, Paul McKenna, David Neely The broad energy spectrum that typically results from target normal sheath acceleration (TNSA) may be well suited to applications such as isochoric heating of matter and proton imaging. However, routine conversion efficiencies of a few percent must be increased to make such concepts truly feasible. A significant enhancement in the yield of laser accelerated protons has been achieved with the use of two laser pulses, narrowly separated in time (Markey et al. PRL 195008 2010). We present results and latest analysis from two experimental campaigns that have sought to increase the proton conversion efficiency further through similar multi-pulse regimes. In the first instance an optimized double-pulse interaction (pulse spacing of 1 ps) was applied in the recirculating electron regime (through the use of thin, $<$ 5$\mu$m, targets) resulting in a conversion efficiency of $\approx15\%$. In a following campaign a novel half-cavity target, consisting of a planar foil with a quarter-sphere attached, was employed. When using such a target the reflected laser light from the primary interaction is collected and refocused back onto the same point, creating a high intensity, double-pulse interaction. Both significant flux enhancement and low energy spectral modification were observed. [Preview Abstract] |
Tuesday, October 30, 2012 3:36PM - 3:48PM |
JO5.00009: Transport material dependence and structure effects on high-charge proton beams C. McGuffey, A. Link, D.C. Gautier, J. Kim, S. Kerr, G.E. Kemp, R. Madden, E.M. Giraldez, M.S. Wei, R.B. Stevens, M.E. Foord, H.S. McLean, P.K. Patel, F.N. Beg The ultimate focal size of a proton beam produced by laser-irradiation of a curved foil can be affected by surrounding structures and self-fields [1,2]. The focusing can further be affected as the beam transports into plasma. We present experimental measurements taken with the high intensity TRIDENT laser ($75~J, 0.6~ps$) at LANL in which protons were focused into a secondary foil of either Mylar, Al, Cu, or Au. XUV emission from a Au layer on the rear of the transport foil indicated a clear dependence of proton beam focused size on transport foil material with the Au layer producing the tightest spot ($40~\mu m$) in spite of having the highest Z and areal density. A target consisting of a flat foil was also tested to compare with the curved foils. XUV emission in this case was undetectable. Coupling of hot electron energy to the structure supporting the target will also be discussed.\\[4pt] [1] Bartal, et al., \emph{Nature Physics} \textbf{8}, 139 (2012).\\[0pt] [2] M. E. Foord, et al., \emph{Phys. Plasmas}, \textbf{19}, 5 (2012). [Preview Abstract] |
Tuesday, October 30, 2012 3:48PM - 4:00PM |
JO5.00010: Characterisation of the interaction of 40fs, 10J laser pulses with gases of atomic clusters Daniel Symes, Stefan Olsson-Robbie, Hugo Doyle, Hazel Lowe, Chris Price, Damien Bigourd, Siddharth Patankar, Katalin Mecseki, Nicola Booth, Robbie Scott, Alastair Moore, Matthias Hohenberger, Rafael Rodriguez, Edward Gumbrell, Roland Smith The interaction of short, intense laser pulses with clustered gas is distinct from that with monatomic gases since the high density in the cluster enables efficient energy deposition. The dramatic heating of the clusters transfers a large portion of the laser energy into ions and, with deuterated gases, can provide a pulsed neutron source. After the laser pulse, hot plasma remains that provides a debris-free EUV and K-alpha x-ray source. The subsequent explosion launches radiative shock waves that are suitable for laboratory astrophysics experiments. Our experiment uses the Astra-Gemini laser with energies above 10J, whereas most studies have been limited to of order 1J. We will characterise blast waves through optical imaging and time-resolved x-ray measurements to determine thresholds for radiative instabilities. We will also study secondary source generation by measuring x-ray, electron and ion yields. In particular we will investigate wakefield acceleration and the associated betatron hard x-ray emission and present a direct comparison with a helium gas experiment to determine the influence of clusters. [Preview Abstract] |
Tuesday, October 30, 2012 4:00PM - 4:12PM |
JO5.00011: Tracking the surface motion of nanometer-scale foils during interactions with ultra-intense laser pulses Matthew Streeter, Zulfikar Najmudin, Steven Cousens, Brendan Dromey, Mark Yeung, Matt Zepf, Jianhui Bin, Christian Kreuzer, Wenjun Ma, J\"urgen Meyer-ter-Vehn, J\"org Schreiber, Peta Foster, Rajeev Pattathil, Christopher Spindloe The surface motion of nanometer-scale foils during irradiation by a relativistically intense ($>$~$10^{20}$~W$/$cm$^{-2}$) laser pulse has been measured using frequency resolved optical gating (FROG) revealing the acceleration of the plasma boundary due to radiation pressure of the laser. Extreme acceleration $\approx 10^{20}$~ms$^{-2}$ leads to velocities $\approx 1$~\% of the speed of light within the duration (50~fs FWHM) of the incident pulse. This gives maximum proton energies from hole-boring acceleration of a few MeV, lower than the experimentally observed maximum energy. This indicates that acceleration of ions beyond the critical surface is occurring, such as is described by sheath acceleration where fast electrons propagate through the plasma to create an accelerating field at the rear surface. For these interactions, which had a pulse contrast of $10^{6}$ at 1~ps, evidence of initial plasma expansion towards the laser was observed, followed by inward acceleration during the most intense period of the pulse. Targets thinner than the relativistic skin-depth appear to become significantly transparent to the laser. [Preview Abstract] |
Tuesday, October 30, 2012 4:12PM - 4:24PM |
JO5.00012: A direct evidence of magnetic field induced lateral transport of fast electrons Prashant Kumar Singh, Gourab Chatterjee, Amitava Adak, Amit D. Lad, Saima Ahmed, Ravindra Kumar Gattamraju Fast electrons generated in the interaction of intense ultrashort laser pulses with solid targets have important roles in both fundamental physics and in technological application such as fast ignition fusion. A fast electron beam propagating into the cold target excites strong self-generated electric and magnetic fields, which in turn govern the transport of the beam itself. These strong fields can deviate the fast electrons propagating into the target and can confine them along the target surface. We observe an ultrafast surface ionization wave from the reflectivity signal driven by the interaction of 3$\times{10}^{17} W cm^{-2}$ intense pulse with a glass target. The reflectivity signal is found to expand three times the initially photoexcited volume, driven by the lateral transport of fast electrons. A simultaneous measurement of the evolution of the generated megagauss magnetic field reveals the direct role of anomalous resistivity in governing the transport of the fast electrons. The similarity in the spatial extent of reflectivity and magnetic field signals indicate that the surface transport is induced by the magnetic field. The lateral transport of fast electrons is explained using a model of magnetic field diffusion. [Preview Abstract] |
Tuesday, October 30, 2012 4:24PM - 4:36PM |
JO5.00013: Mapping magnetic fields at near-solid-densities in laser-produced plasmas using a third-harmonic probe Amit Lad, Gourab Chatterjee, Prashant K. Singh, Amitava Adak, P. Brijesh, G. Ravindra Kumar Relativistic hot electrons in laser-produced plasmas are studied intensively due to their numerous applications including fast ignition. Here, we report the transport of such hot electrons in near-solid-density plasmas. Using the first, second and third harmonics as the probe, we map the self-generated giant magnetic fields starting from the critical solid density $n_c$ up to highly overdense near-solid densities of $9n_c$, almost an order of magnitude higher. This technique is based on the change in the state of polarization of a weak, time-delayed probe pulse reflecting from the plasma created by the interaction pulse at relativistic intensities (800 nm, 30 fs, $10^{18}$ W/cm$^{2}$). We will discuss the advantages of using an externally launched third harmonic probe over self-generated harmonics and other techniques. We will also present the coalescence of the current filaments and the localization of the magnetic fields with sub-picosecond time resolution and micron-level spatial resolution, along with its implications for the hot electron transport. [Preview Abstract] |
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