Bulletin of the American Physical Society
59th Annual Meeting of the APS Division of Plasma Physics
Volume 62, Number 12
Monday–Friday, October 23–27, 2017; Milwaukee, Wisconsin
Session NO6: Laser-Matter Interactions |
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Chair: Chuang Ren, University of Rochester Room: 202C |
Wednesday, October 25, 2017 9:30AM - 9:42AM |
NO6.00001: Blast-Wave Generation and Propagation in Rapidly Heated Laser-Irradiated Targets S.T. Ivancic, C.R. Stillman, P.M. Nilson, A.A. Solodov, D.H. Froula Time-resolved extreme ultraviolet (XUV) spectroscopy was used to study the creation and propagation of a $>$100-Mbar blast wave in a target irradiated by an intense ($>10^{18} \quad {\mbox{W}} \mathord{\left/ {\vphantom {{\mbox{W}} {\mbox{cm}^{2}}}} \right. \kern-\nulldelimiterspace} {\mbox{cm}^{2}})$ laser pulse. Blast waves provide a platform to generate immense pressures in the laboratory. A temporal double flash of XUV radiation was observed when viewing the rear side of the target, which is attributed to the emergence of a blast wave following rapid heating by a fast-electron beam generated from the laser pulse. The time-history of XUV emission in the photon energy range of 50 to 200 eV was recorded with an x-ray streak camera with 7-ps temporal resolution. The heating and expansion of the target was simulated with an electron transport code coupled to 1-D radiation--hydrodynamics simulations. The temporal delay between the two flashes measured in a systematic study of target thickness and composition was found to evolve in good agreement with a Sedov--Taylor blast-wave solution. This material is based upon work supported by the Department of Energy National Nuclear Security Administration under Award Number DE-NA0001944 and Department of Energy Office of Science Award Number DE-SC-0012317. [Preview Abstract] |
Wednesday, October 25, 2017 9:42AM - 9:54AM |
NO6.00002: Characterization of short-pulse laser-produced x-rays for diagnosing magnetically driven cylindrical isentropic compression Hiroshi Sawada, Tyler Daykin, Bruno Bauer, Farhat Beg We have developed an experimental platform to study material properties of magnetically compressed cylinder using a 1 MA pulsed power generator Zebra and a 50 TW subpicosecond short-pulse laser Leopard at the UNR's Nevada Terawatt Facility. According to a MHD simulation, strong magnetic fields generated by 100 ns rise time Zebra current can quasi-isentropically compress a material to the strongly coupled plasma regime. Taking advantage of the cylindrical geometry, a metal rod can be brought to higher pressures than that in the planar geometry. To diagnose the compressed rod with high precision x-ray measurements, an initial laser-only experiment was carried out to characterize laser-produced x-rays. Interaction of a high-intensity, short-pulse laser with solids produces broadband and monochromatic x-rays with photon energies high enough to probe dense metal rods. Bremsstrahlung was measured with Imaging plate-based filter stack spectrometers and monochromatic 8.0 keV Cu K-alpha was recorded with an absolutely calibrated Bragg crystal spectrometer. The broadband x-ray source was applied to radiography of thick metal objects and different filter materials were tested. The experimental results and a design of a coupled experiment will be presented. [Preview Abstract] |
Wednesday, October 25, 2017 9:54AM - 10:06AM |
NO6.00003: Physics of Short Laser Pulse Heated Solid Targets Revealed by Code Comparisons Richard London, Andreas Kemp, Mark Sherlock, Nathan Sircombe, Martin Ramsay Physical properties of hot dense plasmas, such as opacity and equation-of-state, are increasingly being studied with solid targets heated by short-pulse lasers. In the conventional scenario, an intense laser pulse produces hot electrons, which then heat the bulk of the target. However, there remain many unanswered questions about the physics of the energy coupling and transport in such targets. To answer these questions, we have embarked on a project to compare simulation results produced by several independent computer codes. We describe the role of pre-plasma scale length in determining the hot electron spectra and the importance of various coupling mechanisms between hot electrons and the bulk plasma. We discuss plans to identify optimal simulation methods to better utilize short pulse heated targets for studying hot dense matter. [Preview Abstract] |
Wednesday, October 25, 2017 10:06AM - 10:18AM |
NO6.00004: Abstract Withdrawn
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Wednesday, October 25, 2017 10:18AM - 10:30AM |
NO6.00005: Modeling dynamic plasmas driven by ultraintense nano-focused x-ray laser pulses in solid iron targets Ryan Royle, Yasuhiko Sentoku, Roberto Mancini The hard x-ray free electron laser has proven to be a valuable tool for high energy density (HED) physics as it is able to produce well-characterized samples of HED matter at exactly solid density and homogeneous temperatures. However, if the x-ray pulses are focused to sub-micron spot sizes, where peak intensities can exceed 10$^{\mathrm{20}}$ W/cm$^{\mathrm{2}}$, the plasmas driven by sources of non-thermal photoelectrons and Auger electrons can be highly dynamic and so cannot be modeled by atomic kinetics or fluid codes. We apply the 2D/3D particle-in-cell code, PICLS---which has been extended with numerous physics models to enable the simulation of XFEL-driven plasmas---to the modeling of such dynamic plasmas driven by nano-focused XFEL pulses in solid iron targets. In the case of the smallest focal spot investigated of just 100 nm in diameter, keV plasmas induce strong radial E-fields that accelerate keV ions radially as well as sheath fields that accelerate surface ions to hundreds of keV. The heated spot, which is initially larger than the laser spot due to the kinetic nature of the fast Auger electrons, expands as ion and electron waves propagate radially, leaving a low density region along the laser axis. [Preview Abstract] |
Wednesday, October 25, 2017 10:30AM - 10:42AM |
NO6.00006: Proton radiography of relativistic magnetic reconnection driven by ultra-high intensity lasers Paul T. Campbell, A. Raymond, C. A. J. Palmer, Y. Ma, H. Chen, Y. Katzir, C. Mileham, P. M. Nilson, C. P. Ridgers, A. G. R. Thomas, E. R. Tubman, M. S. Wei, G. J. Williams, N. Woolsey, L. Willingale, K. Krushelnick In recent experiments conducted with the OMEGA-EP laser facility at LLE and the Vulcan laser at RAL, proton radiography was used to observe in detail the magnetic field dynamics associated with magnetic reconnection driven by ultra-high intensity, short pulse lasers. Two configurations were investigated: one with two short pulses focused on target in close proximity and another with a short pulse fired near a relatively slowly evolving long pulse produced plasma. The proton radiography results, along with x-ray imaging and angularly resolved electron spectra will be presented. [Preview Abstract] |
Wednesday, October 25, 2017 10:42AM - 10:54AM |
NO6.00007: Magnetic field generation in intense laser-plasma interaction and their impact on ion acceelration Rohini Mishra, Maxence Gauthier, Chandra Curry, Jongjin Kim, Siegfried Glenzer, Frederico Fiuza Mass limited targets can bring advantages to laser-driven ion acceleration including enhanced laser absorption and higher proton energy. However, these targets can be subject to pre-expansion due to the laser pre-pulse and form low-density plasma in the rear side of the target. We have investigated the generation of magnetic fields in pre-expanded targets and the role of these fields on the ion beams. Multidimensional (2D and 3D) particle-in-cell (PIC) simulations motivated by ion acceleration experiments show two dominant magnetic fields generation mechanisms: i) Weibel or current-filamentation instability associated with the background return current and ii) Biermann Battery or fountain effect (associated with fast electron dynamics). They can both contribute to modulate the ion beams. The interplay between these two mechanisms depends on the pre-plasma scale length present at the rear surface of the target. We also present an analytical model to estimate the magnetic fields based on proton energies and modulations observed in the experiments, which is consistent with the PIC simulation results. This work is supported by DOE FES under FWP 100182 and FWP 100237. [Preview Abstract] |
Wednesday, October 25, 2017 10:54AM - 11:06AM |
NO6.00008: Probing the onset of laser-induced relativistic transparency in massive targets Tao Wang, Craig Wagner, Toma Toncian, Gilliss Dyer, Alexey Arefiev, Todd Ditmire We have investigated a novel approach of using harmonics of the laser frequency generated in the plasma to detect the onset of relativistic transparency induced by an intense laser pulse. The onset of the transparency is directly associated with a forward motion of a relativistically adjusted critical surface. The corresponding velocity is relativistic, so the harmonics generated at this critical surface are noticeably shifted. Using particle-in-cell simulations, we have confirmed that the resulting shift greatly exceeds the shift produced during a hole-boring process when the relativistic transparency plays no role, which allows us to clearly identify the onset of the relativistic transparency. Experiments that we have carried out at the Texas Petawatt laser showcase this approach. The 3rd harmonic signal detected in experiments with massive targets irradiated at laser intensities around $10^{20}$ W/cm$^2$ has a pronounced shift associated with the relativistic transparency. The shift represents a recession of the relativistically adjusted critical surface with a velocity close to 0.2 c. This approach opens a new possibility of detecting changes in the optical properties of matter induced by intense laser pulses even when no transmission of the laser pulse takes place. [Preview Abstract] |
Wednesday, October 25, 2017 11:06AM - 11:18AM |
NO6.00009: Microwave Emission Spectroscopy of Short Pulse Laser-Produced Plasma in Air Alexander Englesbe, Jennifer Elle, Remington Reid, Adrian Lucero, Hugh Pohle, Serge Kalmykov, Matthew Domonkos, Andreas Schmitt-Sody, Karl Krushelnick Measuring the radiated power spectral density of microwaves from plasmas has long been used to infer details about plasma behavior. We apply this technique to plasma generated via ultra-short pulse laser ionization. The impulsive interaction of the laser with the plasma drives current, which couples to radiated fields and is a source of broadband terahertz and microwave radiation. We measure the radiated spectrum and angular distribution in the far field over a frequency range of 1-40 GHz. The spectrum of the microwaves is sampled using calibrated, tunable heterodyne receivers. We show that neutral gas pressure significantly alters the amplitude of microwave emissions from the plasma. The spectrum as a function of background neutral density is used to infer information about the free electron density of the plasma. Experimental results are compared to a moving dipole model, with good agreement over a limited parameter range. [Preview Abstract] |
Wednesday, October 25, 2017 11:18AM - 11:30AM |
NO6.00010: Laser pulse sharpening with electromagnetically induced transparency in plasma Kenan Qu, Nathaniel Fisch We propose a laser-controlled plasma shutter technique to generate sharp laser pulses using a process analogous to electromagnetically induced transparency in atoms. The shutter is controlled by a laser with moderately strong intensity, which induces a transparency window below the cutoff frequency, and hence enables propagation of a low frequency laser pulse. Numerical simulations demonstrate that it is possible to generate a sharp pulse wavefront (sub-ps) using two broad pulses in high density plasma. The technique can work in a regime that is not accessible by plasma mirrors when the pulse pedestals are stronger than the ionization intensity. [Preview Abstract] |
Wednesday, October 25, 2017 11:30AM - 11:42AM |
NO6.00011: Magnetic field generation in rotating plasma waves driven by co-propagating OAM lasers Yin Shi, Jorge Vieira, Raoul Trines, Bob Bingham, Baifei Shen, Robert Kingham We present a new magnetic field generation mechanism in underdense plasma due to rotating plasma waves driven by co-propagating Laguerre-Gaussian (LG) beating orbital angular momentum (OAM) laser beams with both a different frequency and also different twist index. In this plasma wave, particles oscillate elliptically in the transverse plane with an azimuthally dependent phase. We therefore call it a transverse rotating plasma wave (TRPW). The distribution and evolution of density and electric field in the transverse plane has some special characteristics. We present a linear fluid model of TRPW and also a high order analysis of the electrical current based on particle motion. To the second order, there is a net rotating current leading to the onset of an intense axial magnetic field (up to 0.4 MG), which persists over a long time in the plasma (ps scale). It is different from Inverse Faraday effects. Our analytical predictions are confirmed in three-dimensional particle-in-cell simulations using EPOCH. This new method of magnetic field creation may find applications in charged beam collimation and controlled fusion. [Preview Abstract] |
Wednesday, October 25, 2017 11:42AM - 11:54AM |
NO6.00012: The role of plasma density scale length on the laser pulse propagation and scattering in relativistic regime Masoud Pishdast, Seyed Abolfazl Ghasemi, Jamal Aldin yazdanpanah The role of plasma density scale length on two short and long laser pulse propagation and scattering in under dense plasma have been investigated in relativistic regime using $1D$ PIC simulation. In our simulation, different density scale lengths and also two short and long pulse lengths with temporal pulse duration $\tau_{L} =60\,fs$ and $\tau_{L} =300\,fs$, respectively have been used. It is found that laser pulse length and density scale length have considerable effects on the energetic electron generation. The analysis of total radiation spectrum reveals that, for short laser pulses and with reducing density scale length, more unstable electromagnetic modes grow and strong longitudinal electric field generates which leads to the generation of more energetic plasma particles. Meanwhile, the dominant scattering mechanism is Raman scattering and tends to Thomson scattering for longer laser pulse. [Preview Abstract] |
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