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Title: Tamper asymmetry and its effect on transmission for x-ray driven opacity simulations

Abstract

This paper reports on synthetic transmission results from Lasnex [1] radiation-hydrodynamics simulations of opacity experiments carried out at Sandia National Laboratories' recently upgraded ZR facility. The focus is on experiments utilizing disk targets composed of a half-moon Fe/Mg mixture tamped on either end with 10- m CH and an additional 35- m beryllium tamper accessory on the end facing the spectrometer. Five x-ray sources with peak power ranging from 10 to 24 TW were used in the simulations to heat and backlight the opacity target. The dominant effect is that the beryllium behind the Fe/Mg mixture is denser and more opaque than the beryllium unshielded by metal during the times of greatest importance for the transmission measurement for all drives. This causes the simulated transmission to be lower than expected, and this is most pronounced for the case using the lowest drive power. While beryllium has a low opacity, its areal density is sufficiently high such that the expected reduction of the measured transmission is significant. This situation leads to an overestimate of iron opacity by 10-215% for a photon energy range of 975- 1775 eV for the 10-TW case. It is shown that if the tamper conditions are known,more » the transmission through each component of the target can be calculated and the resulting opacity can be corrected.« less

Authors:
ORCiD logo [1];  [1]; ORCiD logo [1];  [1];  [1];  [1];  [1]; ORCiD logo [1]
  1. Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
Publication Date:
Research Org.:
Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
Sponsoring Org.:
USDOE
OSTI Identifier:
1402644
Report Number(s):
LA-UR-17-25291
Journal ID: ISSN 1070-664X; TRN: US1703119
Grant/Contract Number:
AC52-06NA25396
Resource Type:
Journal Article: Accepted Manuscript
Journal Name:
Physics of Plasmas
Additional Journal Information:
Journal Volume: 24; Journal Issue: 9; Journal ID: ISSN 1070-664X
Publisher:
American Institute of Physics (AIP)
Country of Publication:
United States
Language:
English
Subject:
70 PLASMA PHYSICS AND FUSION TECHNOLOGY

Citation Formats

Morris, H. E., Tregillis, I. L., Hoffman, N. M., Sherrill, M. E., Fontes, C. J., Marshall, A. J., Urbatsch, T. J., and Bradley, P. A. Tamper asymmetry and its effect on transmission for x-ray driven opacity simulations. United States: N. p., 2017. Web. doi:10.1063/1.4994062.
Morris, H. E., Tregillis, I. L., Hoffman, N. M., Sherrill, M. E., Fontes, C. J., Marshall, A. J., Urbatsch, T. J., & Bradley, P. A. Tamper asymmetry and its effect on transmission for x-ray driven opacity simulations. United States. doi:10.1063/1.4994062.
Morris, H. E., Tregillis, I. L., Hoffman, N. M., Sherrill, M. E., Fontes, C. J., Marshall, A. J., Urbatsch, T. J., and Bradley, P. A. 2017. "Tamper asymmetry and its effect on transmission for x-ray driven opacity simulations". United States. doi:10.1063/1.4994062.
@article{osti_1402644,
title = {Tamper asymmetry and its effect on transmission for x-ray driven opacity simulations},
author = {Morris, H. E. and Tregillis, I. L. and Hoffman, N. M. and Sherrill, M. E. and Fontes, C. J. and Marshall, A. J. and Urbatsch, T. J. and Bradley, P. A.},
abstractNote = {This paper reports on synthetic transmission results from Lasnex [1] radiation-hydrodynamics simulations of opacity experiments carried out at Sandia National Laboratories' recently upgraded ZR facility. The focus is on experiments utilizing disk targets composed of a half-moon Fe/Mg mixture tamped on either end with 10- m CH and an additional 35- m beryllium tamper accessory on the end facing the spectrometer. Five x-ray sources with peak power ranging from 10 to 24 TW were used in the simulations to heat and backlight the opacity target. The dominant effect is that the beryllium behind the Fe/Mg mixture is denser and more opaque than the beryllium unshielded by metal during the times of greatest importance for the transmission measurement for all drives. This causes the simulated transmission to be lower than expected, and this is most pronounced for the case using the lowest drive power. While beryllium has a low opacity, its areal density is sufficiently high such that the expected reduction of the measured transmission is significant. This situation leads to an overestimate of iron opacity by 10-215% for a photon energy range of 975- 1775 eV for the 10-TW case. It is shown that if the tamper conditions are known, the transmission through each component of the target can be calculated and the resulting opacity can be corrected.},
doi = {10.1063/1.4994062},
journal = {Physics of Plasmas},
number = 9,
volume = 24,
place = {United States},
year = 2017,
month = 8
}

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  • Recently a so-called electrical asymmetry effect (EAE), which could achieve high-degree separate control of ion flux and energy in dual-frequency capacitively coupled radio-frequency (CCRF) discharges, was discovered theoretically by Heil et al. [J. Phys. D: Appl. Phys. 41, 165202 (2008)] and was confirmed by experiments and theory/numerical simulations later on for electropositive argon discharges. In this work simulations based on particle-in-cell/Monte Carlo collision are performed to study the EAE on electronegative oxygen plasmas in geometrically symmetric CCRF discharges. Dual frequency discharges operating at 13.56 and 27.12 MHz are simulated for different pressures and the results are compared with those ofmore » electropositive argon discharges at the same conditions. It is found that in general the EAE on oxygen discharges has similar behavior as on argon discharge: The self-bias voltage {eta} increases monotonically and almost linearly with the increase in the phase angle {theta} between the two driving voltages in the range 0<{theta}<90 deg. , and the maximum ion energy varies by a factor of 3 by adjusting {theta}. However, the ion flux varies with {theta} by {+-}12% for low pressure and by {+-}15% for higher pressure, due primarily to an enhanced plasma series resonance, which then leads to dramatic changes in plasma density, power absorption and consequently the electronegativity. This may place a limitation for achieving separate control of ion energy and flux for electronegative plasma via the EAE.« less
  • A new diagnostic technique is described which makes use of large- diameter (approx.5 cm) thin-walled (approx.10 $mu$m) plastic bubbles to collect neutron-activated tamper material in a laser-driven fusion experiment. The plastic bubble and radioactive material are dissolved in a solvent and counted in a Cerenkov scheme to determine the average tamper at peak compression conditions. The bubble energy flow and other plasma diagnostic characteristics are also briefly discussed. (AIP)
  • In x-ray driven ablation, the preheat effect is caused by the high energy x-rays that pass through the ablator. Thus, the transmission flux can be used to characterize preheat effect in a certain degree. With the radiation temperature being 200 eV, the transmission flux and preheat temperature of pure polymer (CH) have been studied by using the one-dimensional multi-group radiation hydrodynamic code MULTI-1D. By studying the spectrum of the transmitted x-rays, it is found that the energy of the transmitted x-rays is in the range of 2–5 keV for pure CH ablator. This is of importance for selecting a dopant for CHmore » ablator. We also calculated both the preheat temperature of CH near the surface of thick target (47.66 μm) and the transmission flux of a thinner target (38.66 μm). It is found that the more transmission flux leads to the higher preheat temperature. Preheat effect of graded Si-doped CH targets with different doped concentrations has also been studied. The results are consistent with this phenomenon. By analyzing the relationship between the transmission flux and the preheat temperature, we have presented a novel method to evaluate preheat effect in x-ray driven ablation.« less
  • In particle-in-cell (PIC) simulation studies of ion-ion two-stream instability, a reduced ion-to-electron mass ratio is often employed to save computation time. It is tacitly assumed that electrons do not play a significant role in the evolution of the instability as the ion-ion interactions are regarded to occur on time scales much slower than the response time of electrons. However, as the effect of such a reduced mass ratio has never been closely examined, we have studied the evolution of the ion beam driven instability using a one-dimensional electrostatic PIC code by rescaling the simulation parameters according to the ion-electron massmore » ratio. We made a reference simulation run with a mass ratio of 100 first and compared the results to the simulation results using the real mass ratio with parameters rescaled from those of the reduced mass ratio. External electric fields were applied in these simulations, which accelerated the electrons and excited an ion acoustic type instability, forming electron phase space holes. Merging of the electron holes affected the ion dynamics significantly when the reduced mass ratio was used, while the interplay between the electron and ion dynamics became different depending on the rescaling methods in the case of the real mass ratio. Another simulation test with much enhanced external electric field results in similar mass ratio dependence. The present simulation results clearly show that the reduced mass ratio should be used cautiously in PIC simulations as the electron dynamics can modify the ion instabilities significantly by affecting the ion motions.« less