Bulletin of the American Physical Society
58th Annual Meeting of the APS Division of Plasma Physics
Volume 61, Number 18
Monday–Friday, October 31–November 4 2016; San Jose, California
Session JO6: Relativistic HED Science, Direct Laser Acceleration and Applications |
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Chair: Brian Beaudoin, University of Maryland Room: 230 C |
Tuesday, November 1, 2016 2:00PM - 2:12PM |
JO6.00001: High Energy Electron Acceleration from Underdense Plasma Channeling Using the OMEGA EP Laser Thomas Batson, Anthony Raymond, Amina Hussein, Karl Krushelnick, Louise Willingale, Phil Nilson, Dustin Froula, Dan Harberberger, Andrew Davies, Wolfgang Theobald, Jackson Williams, Hui Chen, Alexey Arefiev For intense, ps scale lasers, propagation through underdense plasmas results in forces which expel electrons from along the laser axis, resulting in the formation of channels. [1] Electrons can then be injected from the channel walls into the laser path, which results in the direct laser acceleration (DLA) of these electrons and the occurrence of an electron beam of 100’s of MeV. [2] Experiments performed at the OMEGA EP laser studied the formation of a laser channel in an underdense CH plasma, as well as the spatial properties and energy of an electron beam created via DLA mechanisms. The 4 omega optical probe diagnostic was used to characterize the density of the plasma plume, while proton radiography was used to observe the electromagnetic fields of the channel formation. These electric fields as well as the spectra of the accelerated electrons have been studied across different plasma density profiles. The channel behavior and electron spectra are compared to 2D particle-in-cell simulations. [1] Willingale, L. et al., PRL 106 105022 (2011) [2] Willingale, L. et al., NJOP 15 25023 (2013) [Preview Abstract] |
Tuesday, November 1, 2016 2:12PM - 2:24PM |
JO6.00002: Experimental investigation of the transition between relativistic transparency propagation and hole boring in critical surface motion during relativistic laser-plasma interactions Craig Wagner, Andrew Yandow, Gilliss Dyer, Toma Toncian, Alexey Arefiev, Tao Wang, Hernan Quevedo, Rebecca Roycroft, Griffin Glenn, Hailey Van Hoorn, Bjorn Manuel Hegelich, Todd Ditmire An experimental investigation of the transition between relativistic transparency (RT) and hole boring (HB) dominated motion of the electron critical surface during intense laser-plasma interactions is presented. The recession velocity of the critical surface away from the incident laser pulse is measured by imaging second and third harmonic light created during the laser-plasma interaction to bulk spectrometers and measuring spectral shifts due to the surface motion for each shot. Observing differences between the 4$n_{c}$ and 9$n_{c}$ surface motions is useful for diagnosing the physics of the laser-plasma interaction. Experimental results and simulations show that for intensities near $10^{20}$W/$cm^2$ and laser pulse duration shorter than 200fs HB plays little role in critical surface movement when a realistic preplasma is present. The dominant cause of critical surface motion appears to be controlled by preplasma density profile and the intensity time rate of change of the laser pulse. Data from experiments at pulse lengths consistent with the transition between RT and HB dominance will be presented. [Preview Abstract] |
Tuesday, November 1, 2016 2:24PM - 2:36PM |
JO6.00003: Wavelength and Intensity Dependence of the Standing Wave Mechanism in the Near-IR Regime in Producing High Energy Backwards Electron Beams Gregory Ngirmang, Chris Orban, Scott Feister, John Morrison, Enam Chowdhury, William Roquemore Laser-plasma interactions involving ultra-short ultra-intense, near IR or IR wavelength lasers represent a novel regime, specifically inducing relativistic dynamics of charges at lower intensities than required for current ultra-intense lasers. We present 2D(3$v$) Particle-in-Cell(PIC) simulations using the LSP code that produce super-ponderomotive MeV electron beams from ultra-short ultra-intense IR or Near-IR laser beams incident on targets with significant pre-plasma. We perform simulations across different wavelengths, including 800 nanometer, 3 microns, and 10 microns. We also simulate different pulse energies varying from tens of microjoules to tens of joules, and different scale lengths of pre-plasma. The accelerated electrons energies reach super-ponderomotive energies that scale roughly with the normalized vector potential, in line with the standing wave acceleration mechanism discussed in Orban et. al. The angular spectrum of ejected electrons in all cases are similar, displaying preferred angles as suggested by the elaborations on the standing wave mechanism explained in Ngirmang, et. al. [Preview Abstract] |
Tuesday, November 1, 2016 2:36PM - 2:48PM |
JO6.00004: Relativistic electron beam transport through cold and shock-heated carbon samples from aerogel to diamond C. M. Krauland, M. Wei, S. Zhang, J. Santos, P. Nicolai, W. Theobald, J. Kim, P. Forestier-Colleoni, F. Beg Understanding the transport physics of a relativistic electron beam in various plasma regimes is crucial for many high-energy-density applications, such as fast heating for advanced ICF schemes and ion sources. Most short pulse laser-matter interaction experiments for transport studies have been performed with initially cold targets where the resistivity is far from that in warm dense plasmas. We present three experiments that have been performed on OMEGA EP in order to extend fast electron transport and energy coupling studies in pre-assembled plasmas from different carbon samples. Each experiment has used one 4 ns long pulse UV beam (10$^{\mathrm{14}}$ W/cm$^{\mathrm{2}})$ to drive a shockwave through the target and a 10 ps IR beam (10$^{\mathrm{19}}$ W/cm$^{\mathrm{2}})$ to create an electron beam moving opposite the shock propagation direction. These shots were compared with initially cold target shots without the UV beam. We fielded three different samples including 340 mg/cc CRF foam, vitreous carbon at 1.4 g/cc, and high density carbon at 3.4 g/cc. Electrons were diagnosed via x-ray fluorescence measurements from a buried Cu tracer in the target, as well as bremsstrahlung emission and escaped electrons reaching an electron spectrometer. Proton radiograph was also performed in the foam shots. Details of each experiment, available data and particle-in-cell simulations will be presented. [Preview Abstract] |
Tuesday, November 1, 2016 2:48PM - 3:00PM |
JO6.00005: Escape of laser-accelerated MeV electrons through an extended low-density pre-plasma Scott Feister, C. Orban, J.T. Morrison, G.K. Ngirmang, J. Smith, K.D. Frische, A.C. Peterson, A.J. Klim, E.A. Chowdhury, R.R. Freeman, W.M. Roquemore Ultra-intense laser experiments at the Air Force Research Laboratory demonstrated larger than expected conversion efficiencies from laser energy to $\sim$MeV electrons from short pulse irradiation of a water stream target. We present Particle-in-cell (PIC) simulations of the pulse interaction that include highly-realistic 3D modeling of the pre-plasma phase of the target expansion using the FLASH hydrodynamic code. The addition of this FLASH pre-pulse modeling step resulted in a dramatic increase in over-120-keV electrons exiting the LSP simulation space. Removal of the low-density pre-plasma region in the LSP initial conditions was shown to re-create low efficiency results from earlier simulations due to energetic electrons failing to escape an isolated target. Analysis of particle trajectories indicates that energetic electrons travel relatively unimpeded through the extended pre-plasma, increasing the conversion efficiency significantly. [Preview Abstract] |
Tuesday, November 1, 2016 3:00PM - 3:12PM |
JO6.00006: Relativistic Magnetic Reconnection in the Laboratory Karl Krushelnick, Anthony Raymond, CF Dong, A McKelvey, C Zulick, N Alexander, A Bhattacharjee, PT Campbell, H Chen, V Chvykov, E Del Rio, P Fitzsimmons, W Fox, BX Hou, A Maksimchuk, C Mileham, J Nees, PM Nilson, C Stoekl, AGR Thomas, MS Wei, V Yanovsky, L Willingale Magnetic reconnection is a fundamental plasma process involving an exchange of magnetic energy to plasma kinetic energy through changes in the magnetic field topology. Here we present experimental measurements using the OMEGA EP laser at LLE and the HERCULES laser at the University of Michigan as well as numerical modeling which indicate that relativistic magnetic reconnection can be driven by short-pulse, high-intensity lasers that produce a relativistic plasma along with very strong magnetic fields. Evidence of magnetic reconnection was identified by the plasma's X-ray emission patterns, changes to the electron energy spectrum, and by measuring the time over which reconnection occurs. [Preview Abstract] |
Tuesday, November 1, 2016 3:12PM - 3:24PM |
JO6.00007: X-ray and gamma ray emission from petawatt laser-driven nanostructured metal targets Matthew Hill, Peter Allan, Colin Brown, David Hoarty, Lauren Hobbs, Steven James, Clayton Bargsten, Reed Hollinger, Jorge Rocca, Jaebum Park, Hui Chen, Richard London, Ronnie Shepherd, Riccardo Tommasini, Sam Vinko, Justin Wark, Robin Marjoribanks, David Neely, Chris Spindloe Nano-wire arrays of nickel and gold have been fired at the Orion laser facility using high contrast 1$\omega $ and 2$\omega $ short pulse beams (0.7 ps pulse length, \textgreater 10$^{\mathrm{20}}$ W cm$^{\mathrm{-2}}$ intensity). Time-resolved and time-integrated K-shell and M-shell emission have been characterized and compared to those of flat foils, investigating the capability of these metamaterial coatings to enhance laser-target coupling and X-ray emission. Bremsstrahlung emission of gamma rays and associated pair production via the Bethe-Heitler process have also been investigated by use of 1 mm-thick gold substrates attached to the gold nanowires. We present our latest experimental data and outline some potential future applications. [Preview Abstract] |
Tuesday, November 1, 2016 3:24PM - 3:36PM |
JO6.00008: Energy Density in Aligned Nanowire Arrays Irradiated with Relativistic Intensities: Path to Terabar Pressure Plasmas J Rocca, C Bargsten, R Hollinger, V Shylaptsev, S Wang, A Rockwood, Y Wang, D Keiss, M Capeluto, V Kaymak, A Pukhov, R Tommasini, R London, J Park Ultra-high-energy-density (UHED) plasmas, characterized by energy densities \textgreater 1 x 10$^{\mathrm{8}}$ J cm$^{\mathrm{-3\thinspace }}$and pressures greater than a gigabar are encountered in the center of stars and in inertial confinement fusion capsules driven by the world's largest lasers. Similar conditions can be obtained with compact, ultra-high contrast, femtosecond lasers focused to relativistic intensities onto aligned nanowire array targets. Here we report the measurement of the key physical process in determining the energy density deposited in high aspect ratio nanowire array plasmas: the energy penetration. By monitoring the x-ray emission from buried Co tracer segments in Ni nanowire arrays irradiated at an intensity of 4 x 10$^{\mathrm{19}}$ W cm$^{\mathrm{-2}}$, we demonstrate energy penetration depths of several $\mu $m, leading to UHED plasmas of that size. Relativistic 3D particle-in-cell-simulations validated by these measurements predict that irradiation of nanostructures at increased intensity will lead to a virtually unexplored extreme UHED plasma regime characterized by energy densities in excess of 8 x 10$^{\mathrm{10}}$ J cm$^{\mathrm{-3}}$, equivalent to a pressure of 0.35 Tbar. [Preview Abstract] |
Tuesday, November 1, 2016 3:36PM - 3:48PM |
JO6.00009: Hot deuteron generation and neutron production in deuterated nanowire array irradiated at relativistic intensity Alden Curtis, Chase Calvi, Jim Tinsley, Reed Hollinger, Shoujun Wang, Alex Rockwood, Yong Wang, Conrad Buss, Vyacheslav Shlyaptsev, V Kaymak, Alexander Pukhov, Jorge Rocca Irradiation of arrays of aligned high aspect ratio nanowires with high contrast femtosecond laser pulses of relativistic intensity was recently shown to volumetrically heat near solid density plasmas to multi-KeV energy [1]. Using aligned arrays of deuterated polyethylene nanowires (CD$_{\mathrm{2}})$ irradiated at laser intensities of up to $_{\mathrm{\thinspace }}$1 x 10$^{\mathrm{20\thinspace }}$ W/cm$^{\mathrm{2}}$ we are able to generate near solid density plasmas in which the tail of the deuteron distribution was measured to reach energies of up to 3 MeV, in agreement with particle-in-cell simulations. Comparative measurements conducted using flat CD$_{\mathrm{2}}$ targets irradiated by the same laser pulses show the maximum deuteron energies are sub-MeV. We also observed a 100x increase in the number of neutrons produced as compared to flat CD$_{\mathrm{2}}$ targets irradiated at the same conditions, with the highest yield shots producing above 10$^{\mathrm{6}}$ neutrons per Joule of laser energy. [1] M. A. Purvis, V. N. Shlyaptsev, R. Hollinger, C. Bargsten, A. Pukhov, A. Prieto, Y. Wang, B. Luther, L. Yin, S. Wang, and J. J. Rocca, Nature Photonics \textbf{7}, 769, (2013). [Preview Abstract] |
Tuesday, November 1, 2016 3:48PM - 4:00PM |
JO6.00010: Ultra-intense high orbital angular momentum harmonic generation in plasmas Jorge Vieira, R. Trines, E. P. Alves, J. T. Mendonca, R.A. Fonseca, P. Norreys, R. Bigham, L. O. Silva As an independent degree of freedom, it is in principle possible to manipulate the orbital angular momentum (OAM) independently of any other laser property. The OAM therefore stands in equal foot to any other fundamental property of light, such as its frequency. There are, however, many open questions regarding the ability to control the OAM as an independent degree of freedom. A striking example is high harmonic generation, for which there is no OAM counterpart. Here we investigate a high OAM harmonics technique to generate and amplify high OAM harmonics while preserving the laser frequency. The scheme, based on simulated Raman backscattering [J. Vieira et al Nat. Comms. 7, 10371 (2016)], employs a linearly polarised long pump containing more than one OAM level, and a counter-propagating linearly polarised signal beam. The high OAM harmonics result from angular momentum cascading from modes with lower OAM to the modes with higher OAM. The OAM harmonics spectrum can be tailored according to the OAM contents of the pump. We illustrate the scheme with the generation of prime OAM harmonics, an all-optical realisation of the Green-Tao theorem. We support our theoretical findings with 3D particle-in-cell (PIC) simulations using Osiris [R.A. Fonseca et al, PPCF, 55 124011 (2013)]. [Preview Abstract] |
Tuesday, November 1, 2016 4:00PM - 4:12PM |
JO6.00011: Irradiation of Materials using Short, Intense Ion Beams Peter Seidl, Q. Ji, A. Persaud, E. Feinberg, M. Silverman, A. Sulyman, W.L. Waldron, T. Schenkel, J.J. Barnard, A. Friedman, D.P. Grote, E.P. Gilson, I.D. Kaganovich, A. Stepanov, M. Zimmer We present experiments studying material properties created with nanosecond and millimeter-scale ion beam pulses on the Neutralized Drift Compression Experiment-II at Berkeley Lab. The explored scientific topics include the dynamics of ion induced damage in materials, materials synthesis far from equilibrium, warm dense matter and intense beam-plasma physics. We describe the improved accelerator performance, diagnostics and results of beam-induced irradiation of thin samples of, e.g., tin and silicon. Bunches with \textgreater 3x10$^{\mathrm{10}}$ ions/pulse with 1-mm radius and 2-30 ns FWHM duration and have been created. To achieve the short pulse durations and mm-scale focal spot radii, the 1.2 MeV He$^{\mathrm{+}}$ ion beam is neutralized in a drift compression section which removes the space charge defocusing effect during the final compression and focusing. Quantitative comparison of detailed particle-in-cell simulations with the experiment play an important role in optimizing the accelerator performance and keep pace with the accelerator repetition rate of \textless 1/minute. [Preview Abstract] |
Tuesday, November 1, 2016 4:12PM - 4:24PM |
JO6.00012: Characterisation of Plasma Filled Rod Pinch electron beam diode operation James Macdonald, Simon Bland, Jeremy Chittenden The plasma filled rod pinch diode (aka PFRP) offers a small radiographic spot size and a high brightness source. It operates in a very similar to plasma opening switches and dense plasma focus devices -- with a plasma prefill, supplied via a number of simple coaxial plasma guns, being snowploughed~ along a thin rod cathode, before detaching at the end. The aim of this study is to model the PFRP and understand the factors that affect its performance, potentially improving future output. Given the dependence on the PFRP on the prefill, we are making detailed measurements of the density (10$^{\mathrm{15}}$-10$^{\mathrm{18}}$ cm$^{\mathrm{-3}})$, velocity, ionisation and temperature of the plasma emitted from a plasma gun/set of plasma guns. This will then be used to provide initial conditions to the Gorgon 3D MHD code, and the dynamics of the entire rod pinch process studied. [Preview Abstract] |
Tuesday, November 1, 2016 4:24PM - 4:36PM |
JO6.00013: Measurements of the Backstreaming Proton IONS in the Self-Magnetic Pinch (SMP) Diode Utilizing Copper Activation Technique Michael Mazarakis, Michael Cuneo, Sean Fournier, Mark Johnston, Mark Kiefer, Joshua Leckbee, Sean Simpson, Timothy Renk, Timothy Webb, Nichelle Bennett The results presented here were obtained with an SMP diode mounted at the front high voltage end of the 8-10-MV RITS Self-Magnetically Insulated Transmission Line (MITL) voltage adder. Our experiments had two objectives: first, to measure the contribution of the back-streaming proton currents emitted from the anode target, and second, to evaluate the energy of those ions and hence the actual Anode-Cathode (A-K) gap voltage. The accelerating voltage quoted in the literature is estimated utilizing para-potential flow theories. Thus, it is interesting to have another independent measurement of the A-K voltage. We have measured the back-streaming protons emitted from the anode and propagating through a hollow cathode tip for various diode configurations and different techniques of target cleaning treatment, namely, heating at very high temperatures with DC and pulsed current, with RF plasma cleaning, and with both plasma cleaning and heating. We have also evaluated the A-K gap voltage by energy filtering techniques. * Sandia is operated by Sandia Corporation, a subsidiary of Lockheed Martin Company, for the US DOE NNSA under Contract No. DE- AC04-94AL85000. [Preview Abstract] |
Tuesday, November 1, 2016 4:36PM - 4:48PM |
JO6.00014: How the Inductive Voltage Adder (IVA) output impedance affects impedance dynamics of a Self-Magnetic Pinch (SMP) diode Timothy Renk, Sean Simpson, Timothy Webb, Michael Mazarakis, Mark Kiefer The SMP diode, fielded on the RITS-6 (3.5-8.5 MV) IVA accelerator at Sandia National Laboratories, produces a focused electron beam (\textless 3mm diameter) onto a high Z metal converter for flash x-ray applications. Experiments have been undertaken with two different magnetically insulated transmission line (MITL) center conductors, of 40 and 80 ohms flow impedance. We have operated in-situ heating and discharge-cleaning hardware in the load region, in order to address the tendency of some shots to undergo premature impedance (Z) collapse, defined as a fall in impedance beyond that due to normal movement of electrode plasmas that reduces the effective A-K gap. The goal of heating/cleaning was to reduce the volume of evolving gases near the A-K gap. Despite clear evidence that the cleaning techniques removed the proton portion of beam current, we observed no consistent increase in diode impedance (ZDIODE). This forced an examination of the role that the IVA flow impedance has on ZDIODE. A preliminary conclusion is that ZDIODE should be at least 1.5 times the flow impedance before ZDIODE is a parameter independent of flow impedance. This has implications for SMP as a load for a IVA, since ZDIODE \textgreater 100 ohms has not been consistently demonstrated. Data analysis is ongoing, and latest results will be reported.\\ Acknowledgement: Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000. [Preview Abstract] |
Tuesday, November 1, 2016 4:48PM - 5:00PM |
JO6.00015: Design and Simulation of the Recirculating Crossed-Field Planar Amplifier Steven Exelby, Geoffrey Greening, Nicholas Jordan, David Simon, Yue Ying Lau, Ronald Gilgenbach, Brad Hoff The Recirculating Planar Crossed-Field Amplifier (RPCFA) is a high power microwave device adapted from the Recirculating Planar Magnetron$^{\mathrm{1}}$, developed at the University of Michigan. A travelling-wave, rectangular, meander-line design has been developed in simulation that amplifies a 1.3 MW signal at 3 GHz to approximately 29 MW (13.5 dB) with nearly 53{\%} electronic efficiency. Simulation also shows that the RPCFA is zero-drive stable, e.g., output of any appreciable power is dependent on the presence of an input RF signal. The amplifier was designed to be driven by the Michigan Electron Long Beam Accelerator (MELBA), which is currently configured to deliver a -300 kV, 1-10 kA, 0.3-1.0 \textmu s pulse. Taking these parameters into consideration, a slow wave structure, cathode, and housing were designed using the finite element frequency domain code Ansys HFSS. The cold tube characteristics and RF field structures were then verified using the particle in cell code, MAGIC. Hot tube simulations on MAGIC were also run to calculate the RPCFA's performance, including gain and efficiency. Future work will include building a prototype RPCFA, cold testing, and performing experiments to verify the hot tube simulations. [1] R.M. Gilgenbach, Y.Y. Lau, D.M. French, B.W. Hoff, J. Luginsland, and M. Franzi, ``Crossed field device,'' U.S. Patent US 8 841 867B2, Sep. 23, 2014. [2] Developed by Alliant Techsystems [Preview Abstract] |
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