Bulletin of the American Physical Society
60th Annual Meeting of the APS Division of Plasma Physics
Volume 63, Number 11
Monday–Friday, November 5–9, 2018; Portland, Oregon
Session UO6: HEDP with Short Pulse Laser |
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Chair: Mingsheng Wei, Laboratory for Laser Energetics, Rochester, NY Room: OCC B115-116 |
Thursday, November 8, 2018 2:00PM - 2:12PM |
UO6.00001: Theory and Modeling of Proton Acceleration on the NIF ARC Laser Scott C Wilks, Andreas J Kemp, Joohwan Kim, Daniel H Kalantar, Shaun M Kerr, Derek Mariscal, Farhat N Beg, Christopher S McGuffey, Tammy Yee Wing Ma Recent experiments fielded at the NIF have focused on characterizing the proton beam that results when the ARC laser is incident on solid density targets.* This facility is unique in that it can shoot 4 beams simultaneously, each of which can contain between 250 J (for a pulse length Lp ~ 1 ps) to 900 J (Lp ~ 30 ps) in a roughly oval spot of ~ 60 microns by 120 microns. Since TNSA is the predominant proton acceleration mechanism, the proton energy spectra depend on not only the rear-side plasma scale length, but also on the hot electron energy distribution. We find that the unique combination of long pulses and large spot sizes allows for the creation of nontrivial amounts of hot electrons with energies well in excess of the ponderomotive potential,** which leads to significant sheath fields, even when moderate ( ~ 1e18 W/cm^2) laser intensities are considered. Combined PIC-LSP simulations compare favorably to experimental results. * See invited talk by D. Mariscal, this conference. ** See talk by A. J. Kemp et al., this conference. |
Thursday, November 8, 2018 2:12PM - 2:24PM |
UO6.00002: High Z ion acceleration physics with ultra-intense short pulse laser light Yasuhiko Sentoku, Natsumi Iwata, Masayasu Hata Laser-matter interactions in the relativistic regime where the laser intensity exceeds 1020W/cm2 have opened up innovative applications, e.g. compact particle accelerators. Especially, fast high Z ions are attractive for the nuclear physics and as a source of conventional accelerator. We study the high Z ion acceleration with extreme intense laser light interacting with a thin foil target with a help of a state-of-the-art collisional particle-in-cell code, PICLS. The strong sheath field generated thru the laser-matter interaction enables to ionize atoms on the target surface to highly charge states instantaneously and accelerate them simultaneously. Collisional impact ionizations also proceed and compete to the field ionizations inside the target. The ionization dynamics at the target rear surface is the key to determine the characteristic of the high Z ion acceleration. We see the rapid ionization of the rear surface atoms with the evolution of the sheath field together with collisional ionization waves running from the front side. We derived a simple scaling of the sheath field amplitude theoretically. This scaling is useful to estimate the effect of the field ionization/acceleration. |
Thursday, November 8, 2018 2:24PM - 2:36PM |
UO6.00003: Numerical simulation for enhanced production of energetic deuteron ions for neutron sources using laser beams Atsushi Sunahara, Takashi Asahina, Hideo Nagatomo, Ryohei Hanayama, Kunioki Mima, Hiroki Tanaka, Yoshiaki Kato, Sadao Nakai, Ahmed Hassanein We investigated the effect of the pre-formed plasmas on the target normal sheath acceleration (TNSA) of deuteron ions for neutron source production using laser beams. Hydrodynamic simulations demonstrated the long scale length of the pre-formed plasma at the front of the target foil as well as the decrease of the plasma scale length at the rear side for when the target is irradiated by a pre-pulse. The two-dimensional PIC simulations confirmed that the pre-formed plasma profiles at both sides of the target can be optimized for efficient TNSA acceleration, leading to generation of deuteron ions with a larger amount and higher energy, collimated in the forward direction. Our results show the number of accelerated MeV deuteron ions increases by an order of magnitude in comparison with the no pre-pulse case. |
Thursday, November 8, 2018 2:36PM - 2:48PM |
UO6.00004: The effect of laser pulse duration on proton radiography Louise Willingale, Paul T Campbell, David Canning, Amina E Hussein, Karl Michael Krushelnick, Alexander GR Thomas Proton radiography is a valuable and popular diagnostic for measuring the quasi-static electromagnetic fields generated in high-energy-density (HED) experiments. The qualities of laser-driven, target-normal sheath acceleration (TNSA) proton beams have been previously demonstrated to have excellent laminarity and small virtual source size making them suitable for imaging. The broad-energy range of the TNSA protons allows time-of-flight chirping to observe the temporal evolution of fields on the $\sim 1$--$100$ ps timescales in a single shot and laser parameters influence the choice of optimal target thickness. Here, the OMEGA EP facility was used to experimentally consider the effect of the laser pulse duration (between 1 ps and 100 ps), intensity and target angle of incidence on the proton beam qualities of uniformity, image visibility, energy spectra and divergence. Two-dimensional particle-in-cell modeling examines the acceleration mechanisms to explain the degrading beam quality for longer pulse durations. These results will help guide future experimental and laser system designs. |
Thursday, November 8, 2018 2:48PM - 3:00PM |
UO6.00005: Electron Acceleration in Multi-Kilojoule, Multi-Picosecond Laser Pulses Andreas Kemp, Scott Wilks, Joohwan Kim, Nuno Lemos, Mark Sherlock, Tammy Ma ‘Super-ponderomotive’ electrons have been observed in experiments since the early days of energetic short-pulse laser-plasma interaction on NOVA-PW [Perry, RevSciInst1999], but they were largely ignored due to their relatively small number. Longer pulses, plasma density gradients and higher intensities favor the generation of an additional ‘super-ponderomotive’ electron population, at energies much larger than the ponderomotive potential. Recent 1D PIC simulations [Sorokovikova, Phys.Rev.Lett.2017], give twenty times larger MeV electron doses than in the NOVA-PW case. Such an enhancement would boost applications from proton acceleration (see talks by D.Mariscal and S.C.Wilks, this conference) to MeV x-ray generation and the creation of electron-positron plasmas. We discuss electron acceleration to super-ponderomotive energies in laser-solid interaction of multi-kilojoule, multi-picosecond pulses at the relativistic threshold, e.g. NIF-ARC, with 1D and quasi-2D Particle-in-Cell simulations. |
Thursday, November 8, 2018 3:00PM - 3:12PM |
UO6.00006: Formation of power law energy distribution via stochastic process in a relativistic laser-driven bouncer Natsumi Iwata, Yasuhiko Sentoku, Takayoshi Sano, Kunioki Mima Non-Maxwellian energy distributions are ubiquitous in nature, many of which are considered to be generated via non-thermal stochastic interactions.The well-known example is the power law energy distribution of cosmic rays described by the Fermi acceleration [1]. We found that picosecond (ps) relativistic laser-foil interactions can result a stochastic electron acceleration [2] which resembles the Fermi acceleration described by the bouncer model [3]. In the ps interaction, superthermal electrons increase especially after the transition from the hole boring to the plasma blowout [4]. Based on the Fokker-Planck equation, we developed a theory of power law electron spectrum formation in the laser-foil system. We found that the p2 difference between acceleration (diffusion) and dissipation in the blowout phase leads a power law distribution with index given by the ratio of the dissipation and diffusion coefficients. The kJ-class laser experiments thus can be a platform for investigating energy distribution formation in collisionless plasmas. [1] E. Fermi, Phys. Rev. 75, 1169 (1949), [2] N. Iwata et al., Phys. Plasmas 24, 073111 (2017),[3] A. J. Lichtenberg, et al., Physica 1D, 291 (1980),[4] N. Iwata et al., Nat. Commun. 9, 623 (2018). |
Thursday, November 8, 2018 3:12PM - 3:24PM |
UO6.00007: Heating a solid isochorically over keV temperature by a multi-picosecond intense laser light Naoki Higashi, Natsumi Iwata, Takayoshi Sano, Kunioki Mima, Yasuhiko Sentoku We study isochoric heating via diffusive heat transport driven by multi-picosecond (ps) relativistic laser light. Intense lasers can heat dense plasmas via collisional processes, i.e. resistive heating, drag heating, and/or diffusive heating. Since the laser is stopped at the critical density, the laser produced relativistic electron beam (REB) has been considered as only the candidate to heat the dense plasmas via resistive heating or drag heating. However, the efficiency is low to heat the plasmas volumetrically over keV temperature. By improving the contrast ratio a kJ ps laser, LFEX, realizes the direct interaction of the intense laser light with a solid surface. Because of the direct interaction, the plasma is heated over keV temperature diffusively. Here we study the heating processes using a collisional two-dimensional Particle-in-Cell code, PICLS, and found that the diffusive heat wave reaches to a few micron inside the solid surface in ps time scale. The theoretical scaling of diffusive heating and the laser condition that realizes the diffusive heating during the laser-plasma interaction will be presented. The creation of large volume keV solid plasmas opens a new path to explore the high energy density science. |
Thursday, November 8, 2018 3:24PM - 3:36PM |
UO6.00008: Direct Ion Heating in Overdense Plasmas by a Standing Whistler Wave Takayoshi Sano, Masayasu Hata, Natsumi Iwata, Kunioki Mima, Yasuhiko Sentoku Interaction of overdense plasmas with counter-irradiating relativistic intensity lasers under a strong magnetic field is investigated by one-dimensional Particle-in-Cell simulations. It is found that a large-amplitude ion acoustic wave is excited promptly due to a standing wave formed by the counter propagating Whistler waves. This ion wave appears only when the magnetic field strength is further stronger than the cyclotron resonance condition, which is given by the balance between the laser and electron cyclotron frequencies. Through this process, ions obtain a large amount of energy predominantly and directly from the electromagnetic waves. The ion temperature could be much higher than the electron temperature in this regime. The propagation of a large-amplitude whistler wave under a strong magnetic field could be an interesting mechanism for an efficient heating of ions or electrons in overdense plasmas. |
Thursday, November 8, 2018 3:36PM - 3:48PM |
UO6.00009: Commissioning and use of ARC for pair-plasma generation on NIF Daniel H Kalantar, Hui Chen, Gerald J Williams, David Alessi, Mark Hermann, Andrew G MacPhee, David Martinez, ARC TEAM, Mario Manuel, Frederico Fiuza, Louise Willingale, Joohwan Kim, Farhat N Beg, Mitsuo Nakai Relativistic electron-positron pair plasmas are unique in plasma physics and are thought to play a fundamental role in high energy astrophysical processes such as gamma ray bursts. Short pulse lasers have been shown to generate high density and high-flux pair plasmas. Pair plasma experiments fielded at the National Ignition Facility (NIF) using the Advanced Radiographic Capability (ARC) have demonstrated the creation of electron-positron pairs. ARC currently uses two NIF beamlines, each split into 2 sub-aperture beamlets with 1-38 ps pulse length capability and energies up to 1 kJ per beamlet. By adding a parabolic cone to the front of the target, the light from ARC was re-focused to a high intensity sufficient to generate positrons. Based on the measured electron slope temperature of Te ~ 2-3 MeV, the inferred effective illumination intensity with the cone was approximately 4x1018 W/cm2, higher than expected based on the measured statistical pointing and timing performance for ARC. We will present a summary of ARC performance, describe the pair plasma platform and relevance to future laboratory astrophysics studies. |
Thursday, November 8, 2018 3:48PM - 4:00PM |
UO6.00010: Diagnosing ‘super-ponderomotive’ electron energy distribution with electron-positron pair production at LFEX Yasunobu Arikawa, Alessio Morace, Natsumi Iwata, Jackson Williams, Nuno Lemos, Derek Alexander, Tammy Ma, Felicie Albert, Hui Chen, Kazuki Matsuo, Sadaoki Kojima, Shigeki Tokita, Junji Kawanaka, Yoichi Sakawa, Yasuhiko Sentoku, Shinsuke Fujioka, Hiroyuki Shiraga, Mitsuo Nakai, Ryosuke Kodama Increasing the ‘super-ponderomotive’ electron population in laser-solid interactions would greatly benefit ion acceleration schemes and x-ray and positron generation. In this work we explore the possibility of using long laser pulse durations (~2 ps) than previous (~0.7 ps), large scale length plasmas (tens of microns) and high-laser intensities (1019-1020 W/cm2) to increase the ‘super-ponderomotive’ electron population, at energies beyond the ponderomotive potential. Using the high-intensity laser LFEX we successfully generated ‘super-ponderomotive’ electron distributions by controlling the pre-plasma scale length (changing the laser pulse contrast) and target geometry. As a consequence of the increased ‘super-ponderomotive’ electron distribution, positron beams were generated and enhanced by one order of magnitude with a 9x10-9 pulse contrast and a wedged target. |
Thursday, November 8, 2018 4:00PM - 4:12PM |
UO6.00011: Characterization of laser-produced bremsstrahlung for x-ray radiography of pulsed-power driven mm diameter metal rods Hiroshi Sawada, Tyler Daykin, Trevor M Hutchinson, Bruno S Bauer, Vladimir V. Ivanov, Farhat N Beg A Mega Ampere current pulsed power system with a ~ 100 ns rise time can quasi-isentropically compress a millimeter diameter solid metal rod to strongly coupled plasma. To develop an x-ray source for probing such a plasma, we carried out a short-pulse laser experiment at University of Nevada Reno's Nevada Terawatt Facility using a 50 TW Leopard laser to characterize high energy bremsstrahlung both in a laser and Zebra pulsed power chamber. Bremsstrahlung and fast electrons generated in the laser interaction with silver foils (10, 20 and 100 μm thickness) and a 25 μm diameter silver wire were recorded with a Image plate-based filter stack bremsstrahlung spectrometer and a magnetic electron spectrometer. The x-ray sources were used to obtain x-ray images of undriven Al rods with 0.5, 1.0 and 1.6 mm diameters. Among the targets we studied, the highest x-ray yields were observed with the 10 μm thick foil while the better spatial resolution of the image was obtained with the wire target. The experiment and analysis of the source using hybrid Particle-in-cell simulations will be presented. |
Thursday, November 8, 2018 4:12PM - 4:24PM |
UO6.00012: Investigation of fast electron properties from hybrid-PIC modeling of angularly resolved bremsstrahlung Tyler Daykin, Hiroshi Sawada, Yasuhiko Sentoku, Farhat N Beg, Hui Chen, Harry Scott McLean, Anthony J. Link, Pravesh K Patel, Yuan Ping Characterization of fast electrons generated by ultra-intense short-pulse lasers is important for many high-energy x-ray applications such as broadband Compton radiography and K-a radiography. An experiment was conducted to study the electron energy spectrum, divergence, and conversion efficiency of fast electrons by irradiating a 100 µm thick Cu foil with the 50 TW Leopard laser at the Nevada Terawatt Facility. Bremsstrahlung and escaped electrons were recorded with differential filter stack spectrometers at 22° and 40° from the laser axis and a magnetic electron spectrometer along the laser axis. From measurements with the electron spectrometer, a slope temperature of 1.1 MeV was inferred. Using the inferred electron spectrum in a hybrid particle-in-cell code, LSP, with a 2D Cartesian coordinate, we fit the bremsstrahlung signals at the two angles simultaneously by varying the divergence angle and energy of fast electrons injected. A best fit of the data was found for the conversion efficiency of ~ 6% and a divergence angle of ~10°. Details of this experimental and numerical study will be presented. |
Thursday, November 8, 2018 4:24PM - 4:36PM |
UO6.00013: Emission spectroscopy characterization of an imploded, magnetized cylindrical plasma for relativistic electron transport Maylis M Dozieres, Pierre Forestier-Colleoni, Christopher S McGuffey, Kazuki Matsuo, Mathieu Bailly-Grandvaux, Krish A Bhutwala, Mingsheng S Wei, Christine M Krauland, Pierre-Alexandre Gourdain, Jonathan R Davies, Shinsuke Fujioka, E. M. Campbell, Jonathan L Peebles, Joao J Santos, Dimitri Batani, Shu Zhang, Farhat N Beg We report on experiments performed on the Omega laser facility to investigate the propagation of relativistic electrons in a compressed, magnetized cylindrical plasma. A cylindrical target composed of a CH foam doped with 1% Cl within a tube of solid CH was irradiated by 36 OMEGA beams to compress the CH together with an applied, axial magnetic field. The cylinder ends were capped with Cu and Zn foils. We used emission spectroscopic techniques to characterize the imploded plasma and to supplement the electron propagation data. The analysis of the time-resolved continuum emission from the foam and Cl K-shell emission as well as time-integrated Cu and Zn K-shell emission are presented for targets with and without the applied field. Temperatures and densities are inferred using atomic physics code simulations and compared to 2D hydrodynamic calculations from FLASH code. Additional emission was observed, and electron spectra were recorded when the OMEGA EP laser, used to generate the relativistic electrons, irradiated the Zn endcap giving information about propagation and energy deposition of the relativistic electrons. |
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