Matter and Radiation at Extremes
Co-Editors-in-Chief
Weiyan Zhang; Ho-Kwang Mao; Michel Koenig
2022
Volume: 7 Issue 2
7 Article(s)
B. Martinez, S. N. Chen, S. Bolaños, N. Blanchot, G. Boutoux, W. Cayzac, C. Courtois, X. Davoine, A. Duval, V. Horny, I. Lantuejoul, L. Le Deroff, P. E. Masson-Laborde, G. Sary, B. Vauzour, R. Smets, L. Gremillet, and J. Fuchs

Laser-driven neutron sources could offer a promising alternative to those based on conventional accelerator technologies in delivering compact beams of high brightness and short duration. We examine this through particle-in-cell and Monte Carlo simulations that model, respectively, the laser acceleration of protons from thin-foil targets and their subsequent conversion into neutrons in secondary lead targets. Laser parameters relevant to the 0.5 PW LMJ-PETAL and 0.6–6 PW Apollon systems are considered. Owing to its high intensity, the 20-fs-duration 0.6 PW Apollon laser is expected to accelerate protons up to above 100 MeV, thereby unlocking efficient neutron generation via spallation reactions. As a result, despite a 30-fold lower pulse energy than the LMJ-PETAL laser, the 0.6 PW Apollon laser should perform comparably well both in terms of neutron yield and flux. Notably, we predict that very compact neutron pulses, of ∼10 ps duration and ∼100 μm spot size, can be released provided the lead convertor target is thin enough (∼100 μm). These sources are characterized by extreme fluxes, of the order of 1023 n cm-2 s-1, and even ten times higher when using the 6 PW Apollon laser. Such values surpass those currently achievable at large-scale accelerator-based neutron sources (∼1016 n cm-2 s-1), or reported from previous laser experiments using low-Z converters (∼1018 n cm-2 s-1). By showing that such laser systems can produce neutron pulses significantly brighter than existing sources, our findings open a path toward attractive novel applications, such as flash neutron radiography and laboratory studies of heavy-ion nucleosynthesis.

Matter and Radiation at Extremes
Mar. 15, 2022
  • Vol. 7 Issue 2 024401 (2022)
  • Baojun Zhu, Zhe Zhang, Chang Liu, Dawei Yuan, Weiman Jiang, Huigang Wei, Fang Li, Yihang Zhang, Bo Han, Lei Cheng, Shangqing Li, Jiayong Zhong, Xiaoxia Yuan, Bowei Tong, Wei Sun, Zhiheng Fang, Chen Wang, Zhiyong Xie, Neng Hua, Rong Wu, Zhanfeng Qiao, Guiyun Liang, Baoqiang Zhu, Jianqiang Zhu, Shinsuke Fujioka, and Yutong Li

    The Zeeman splitting effect is observed in a strong magnetic field generated by a laser-driven coil. The expanding plasma from the coil wire surface is concentrated at the coil center and interacts with the simultaneously generated magnetic field. The Cu I spectral lines at wavelengths of 510.5541, 515.3235, and 521.8202 nm are detected and analyzed. The splittings of spectral lines are used to estimate the magnetic field strength at the coil center as ∼31.4 ± 15.7 T at a laser intensity of ∼5.6 × 1015 W/cm2, which agrees well with measurements using a B-dot probe. Some other plasma parameters of the central plasma disk are also studied. The temperature is evaluated from the Cu I spectral line intensity ratio, while the electron density is estimated from the Stark broadening effect.

    Matter and Radiation at Extremes
    Mar. 15, 2022
  • Vol. 7 Issue 2 024402 (2022)
  • Jingui Xu, Dongzhou Zhang, Sergey N. Tkachev, and Przemyslaw K. Dera

    Single-crystal x-ray diffraction (SCXRD) is an important tool to study the crystal structure and phase transitions of crystalline materials at elevated pressures. The Partnership for eXtreme Xtallography (PX2) program at the GSECARS 13-BM-C beamline of the Advanced Photon Source aims to provide state-of-the-art experimental capabilities to determine the crystal structures of materials under extreme conditions using SCXRD. PX2 provides a focused x-ray beam (12 × 18 µm2) at a monochromatic energy of 28.6 keV. High-pressure SCXRD experiments are performed with a six-circle diffractometer and a Pilatus3 photon-counting detector, facilitated by a membrane system for remote pressure control and an online ruby fluorescence system for pressure determination. The efficient, high-quality crystal structure determination at PX2 is exemplified by a study of pressure-induced phase transitions in natural ilvaite [CaFe2+2Fe3+Si2O7O(OH), P21/a space group]. Two phase transitions are observed at high pressure. The SCXRD data confirm the already-known ilvaite-I (P21/a) → ilvaite-II (Pnam) transformation at 0.4(1) GPa, and, a further phase transition is found to occur at 22.8(2) GPa where ilvaite-II transforms into ilvaite-III (P21/a). The crystal structure of the ilvaite-III is solved and refined in the P21/a space group. In addition to the ilvaite-I → ilvaite-II → ilvaite-III phase transitions, two minor structural modifications are observed as discontinuities in the evolution of the FeO6 polyhedral geometries with pressure, which are likely associated with magnetic transitions.

    Matter and Radiation at Extremes
    Mar. 15, 2022
  • Vol. 7 Issue 2 028401 (2022)
  • Guangwei Meng, Jun She, Tianming Song, Jiamin Yang, and Min Wang

    Experiments exploring the propagation of heat waves within cylindrical CH foams were performed on the Shenguang-III prototype laser facility in 2012. In this paper, the radiation fluxes out of CH foam cylinders at different angles are analyzed theoretically using the two-dimensional radiation hydrodynamics code LARED-R. Owing to the difficulty in validating opacity and equation of state (EOS) data for high-Z plasmas, and to uncertainties in the measured radiation temperature Tr and the original foam density ρ0, multipliers are introduced to adjust the Au material parameters, Tr, and ρ0 in our simulations to better explain the measurements. The dependences of the peak radiation flux Fmax and the breakout time of the heat wave thalf (defined as the time corresponding to the radiation flux at half-maximum) on the radiation source, opacity, EOS, and ρ0 scaling factors (ηsrc, ηop, ηeos, and ηρ) are investigated via numerical simulations combined with fitting. Then, with the uncertainties in the measured Tr and ρ0 fixed at 3.6% and 3.1%, respectively, experimental data are exploited as fiducial values to determine the ranges of ηop and ηeos. It is found that the ranges of ηop and ηeos fixed by this experiment overlap partially with those found in our previous work [Meng et al., Phys. Plasmas 20, 092704 (2013)]. Based on the scaled opacity and EOS parameters, the values of Fmax and thalf obtained via simulations are in good agreement with the measurements, with maximum errors ∼9.5% and within 100 ps, respectively.

    Matter and Radiation at Extremes
    Mar. 15, 2022
  • Vol. 7 Issue 2 025901 (2022)
  • E. Kh. Baksht, B. A. Alekseev, A. G. Burachenko, A. V. Vukolov, A. P. Potylitsyn, V. F. Tarasenko, S. R. Uglov, and M. V. Shevelev

    Fused silica and KBr samples were irradiated with a 2.7 MeV electron beam. The emission of fused silica and KBr samples in the UV and visible regions was studied under various experimental conditions. Numerical simulation of optical emission was carried out using the GEANT4 computer platform. Simulations of energy spectra and angular distributions of the beam electrons were performed for different target thicknesses. The results reveal the effect of scattering of the beam electrons on the angular distribution of Cherenkov radiation in fused silica samples with thicknesses exceeding the electron path length.

    Matter and Radiation at Extremes
    Mar. 15, 2022
  • Vol. 7 Issue 2 026901 (2022)
  • C. Samulski, B. Srinivasan, M. J.-E. Manuel, R. Masti, J. P. Sauppe, and J. Kline

    Experiments have identified the Rayleigh–Taylor (RT) instability as one of the greatest obstacles to achieving inertial confinement fusion. Consequently, mitigation strategies to reduce RT growth and fuel–ablator mixing in the hotspot during the deceleration phase of the implosion are of great interest. In this work, the effect of seed magnetic fields on deceleration-phase RT growth are studied in planar and cylindrical geometries under conditions relevant to the National Ignition Facility (NIF) and Omega experiments. The magnetohydrodynamic (MHD) and resistive-MHD capabilities of the FLASH code are used to model imploding cylinders and planar blast-wave-driven targets. Realistic target and laser parameters are presented that suggest the occurrence of morphological differences in late-time RT evolution in the cylindrical NIF case and a measurable difference in spike height of single-mode growth in the planar NIF case. The results of this study indicate the need for target designs to utilize an RT-unstable foam–foam interface in order to achieve sufficient magnetic field amplification to alter RT evolution. Benchmarked FLASH simulations are used to study these magnetic field effects in both resistive and ideal MHD.

    Matter and Radiation at Extremes
    Mar. 15, 2022
  • Vol. 7 Issue 2 026902 (2022)
  • Weipeng Yao, Julien Capitaine, Benjamin Khiar, Tommaso Vinci, Konstantin Burdonov, Jérôme Béard, Julien Fuchs, and Andrea Ciardi

    Magnetized laser-produced plasmas are central to many studies in laboratory astrophysics, in inertial confinement fusion, and in industrial applications. Here, we present the results of large-scale three-dimensional magnetohydrodynamic simulations of the dynamics of a laser-produced plasma expanding into a transverse magnetic field with a strength of tens of teslas. The simulations show the plasma being confined by the strong magnetic field into a slender slab structured by the magnetized Rayleigh–Taylor instability that develops at the plasma–vacuum interface. We find that when the initial velocity of the plume is perturbed, the slab can develop kink-like motions that disrupt its propagation.

    Matter and Radiation at Extremes
    Mar. 15, 2022
  • Vol. 7 Issue 2 026903 (2022)
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