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Title: Source characterization and modeling development for monoenergetic-proton radiography experiments on OMEGA

Abstract

A monoenergetic proton source has been characterized and a modeling tool developed for proton radiography experiments at the OMEGA [T. R. Boehly et al., Opt. Comm. 133, 495 (1997)] laser facility. Multiple diagnostics were fielded to measure global isotropy levels in proton fluence and images of the proton source itself provided information on local uniformity relevant to proton radiography experiments. Global fluence uniformity was assessed by multiple yield diagnostics and deviations were calculated to be {approx}16% and {approx}26% of the mean for DD and D{sup 3}He fusion protons, respectively. From individual fluence images, it was found that the angular frequencies of Greater-Than-Or-Equivalent-To 50 rad{sup -1} contributed less than a few percent to local nonuniformity levels. A model was constructed using the Geant4 [S. Agostinelli et al., Nuc. Inst. Meth. A 506, 250 (2003)] framework to simulate proton radiography experiments. The simulation implements realistic source parameters and various target geometries. The model was benchmarked with the radiographs of cold-matter targets to within experimental accuracy. To validate the use of this code, the cold-matter approximation for the scattering of fusion protons in plasma is discussed using a typical laser-foil experiment as an example case. It is shown that an analytic cold-matter approximationmore » is accurate to within Less-Than-Or-Equivalent-To 10% of the analytic plasma model in the example scenario.« less

Authors:
; ; ; ; ; ; ; ; ;  [1]
  1. Plasma Science and Fusion Center, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, Massachusetts 02139 (United States)
Publication Date:
OSTI Identifier:
22093628
Resource Type:
Journal Article
Resource Relation:
Journal Name: Review of Scientific Instruments; Journal Volume: 83; Journal Issue: 6; Other Information: (c) 2012 American Institute of Physics; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND TECHNOLOGY; ACCURACY; APPROXIMATIONS; BERYLLIUM 16; IMAGES; ISOTROPY; LASER RADIATION; PLASMA; PLASMA DIAGNOSTICS; PLASMA SIMULATION; PROTON RADIOGRAPHY; PROTON SOURCES; PROTONS

Citation Formats

Manuel, M. J.-E., Zylstra, A. B., Rinderknecht, H. G., Casey, D. T., Rosenberg, M. J., Sinenian, N., Li, C. K., Frenje, J. A., Seguin, F. H., and Petrasso, R. D. Source characterization and modeling development for monoenergetic-proton radiography experiments on OMEGA. United States: N. p., 2012. Web. doi:10.1063/1.4730336.
Manuel, M. J.-E., Zylstra, A. B., Rinderknecht, H. G., Casey, D. T., Rosenberg, M. J., Sinenian, N., Li, C. K., Frenje, J. A., Seguin, F. H., & Petrasso, R. D. Source characterization and modeling development for monoenergetic-proton radiography experiments on OMEGA. United States. doi:10.1063/1.4730336.
Manuel, M. J.-E., Zylstra, A. B., Rinderknecht, H. G., Casey, D. T., Rosenberg, M. J., Sinenian, N., Li, C. K., Frenje, J. A., Seguin, F. H., and Petrasso, R. D. Fri . "Source characterization and modeling development for monoenergetic-proton radiography experiments on OMEGA". United States. doi:10.1063/1.4730336.
@article{osti_22093628,
title = {Source characterization and modeling development for monoenergetic-proton radiography experiments on OMEGA},
author = {Manuel, M. J.-E. and Zylstra, A. B. and Rinderknecht, H. G. and Casey, D. T. and Rosenberg, M. J. and Sinenian, N. and Li, C. K. and Frenje, J. A. and Seguin, F. H. and Petrasso, R. D.},
abstractNote = {A monoenergetic proton source has been characterized and a modeling tool developed for proton radiography experiments at the OMEGA [T. R. Boehly et al., Opt. Comm. 133, 495 (1997)] laser facility. Multiple diagnostics were fielded to measure global isotropy levels in proton fluence and images of the proton source itself provided information on local uniformity relevant to proton radiography experiments. Global fluence uniformity was assessed by multiple yield diagnostics and deviations were calculated to be {approx}16% and {approx}26% of the mean for DD and D{sup 3}He fusion protons, respectively. From individual fluence images, it was found that the angular frequencies of Greater-Than-Or-Equivalent-To 50 rad{sup -1} contributed less than a few percent to local nonuniformity levels. A model was constructed using the Geant4 [S. Agostinelli et al., Nuc. Inst. Meth. A 506, 250 (2003)] framework to simulate proton radiography experiments. The simulation implements realistic source parameters and various target geometries. The model was benchmarked with the radiographs of cold-matter targets to within experimental accuracy. To validate the use of this code, the cold-matter approximation for the scattering of fusion protons in plasma is discussed using a typical laser-foil experiment as an example case. It is shown that an analytic cold-matter approximation is accurate to within Less-Than-Or-Equivalent-To 10% of the analytic plasma model in the example scenario.},
doi = {10.1063/1.4730336},
journal = {Review of Scientific Instruments},
number = 6,
volume = 83,
place = {United States},
year = {Fri Jun 15 00:00:00 EDT 2012},
month = {Fri Jun 15 00:00:00 EDT 2012}
}
  • Electromagnetic (E/B) fields generated by the interaction with plasmas of long-pulse, low-intensity laser beams relevant to inertial confinement fusion have been measured for the first time using novel monoenergetic proton radiography methods. High-resolution, time-gated radiography images of a plastic foil driven by a 10{sup 14} W/cm{sup 2} laser implied B fields of {approx}0.5 MG and E fields of {approx}1.5x10{sup 8} V/m. Simulations of these experiments with LASNEX+LSP have been performed and are in overall (though not exact) agreement with the data both for field strengths and for spatial distributions; this is the first direct experimental test of the laser-generated B-fieldmore » package in LASNEX. The experiments also demonstrated that laser phase plates substantially reduce medium-scale chaotic field structure.« less
  • Time-gated, monoenergetic radiography with 15-MeV protons provides unique measurements of implosion dynamics in direct-drive inertial-confinement fusion. Images obtained during acceleration, coasting, deceleration, and stagnation display a comprehensive picture of spherical implosions. Critical information inferred from such images, hitherto unavailable, characterizes the spatial structure and temporal evolution of self-generated fields and plasma areal density. Results include the first observation of a radial electric field inside the imploding capsule. It is initially directed inward (at {approx}10{sup 9} V/m), eventually reverses direction ({approx}10{sup 8} V/m), and is the probable consequence of the evolution of the electron pressure gradient.
  • Backlit pinhole radiography used with ungated film as a detector creates x-ray radiographs with increased resolution and contrast. Current hydrodynamics experiments on the OMEGA Laser use a three-dimensional sinusoidal pattern as a seed perturbation for the study of instabilities. The structure of this perturbation makes it highly desirable to obtain two simultaneous orthogonal backlighting views. We accomplished this using two backlit pinholes each mounted 12 mm from the target. The pinholes, of varying size and shape, were centered on 5 mm square foils of 50 {mu}m thick Ta. The backlighting is by K-alpha emission from a 500 {mu}m square Timore » or Sc foil mounted 500 {mu}m from the Ta on a plastic substrate. Four laser beams overfill the metal foil, so that the expanding plastic provides radial tamping of the expanding metal plasma. The resulting x-rays pass through the target onto (ungated) direct exposure film (DEF). Interference between the two views is reduced by using a nose cone in front of the DEF, typically with a 9 mm Ta aperture and with magnets to deflect electrons. Comparison of varying types of pinholes and film exposures will be presented from recent experiments as well as an analysis of the background noise created using this experimental technique.« less
  • We present the calculations and preliminary results from experiments on the Omega laser facility using d-{sup 3}He filled plastic capsule implosions in gold Hohlraums. These experiments aim to develop a technique to measure shell {rho}r and capsule unablated mass with proton spectroscopy and will be applied to future National Ignition Facility (NIF) experiments with ignition scale capsules. The Omega Hohlraums are 1900 {mu}m lengthx1200 {mu}m diameter and have a 70% laser entrance hole. This is approximately a 0.2 NIF scale ignition Hohlraum and reaches temperatures of 265-275 eV similar to those during the peak of the NIF drive. These capsulesmore » can be used as a diagnostic of shell {rho}r, since the d-{sup 3}He gas fill produces 14.7 MeV protons in the implosion, which escape through the shell and produce a proton spectrum that depends on the integrated {rho}r of the remaining shell mass. The neutron yield, proton yield, and spectra change with capsule shell thickness as the unablated mass or remaining capsule {rho}r changes. Proton stopping models are used to infer shell unablated mass and shell {rho}r from the proton spectra measured with different filter thicknesses. The experiment is well modeled with respect to Hohlraum energetics, neutron yields, and x-ray imploded core image size, but there are discrepancies between the observed and simulated proton spectra.« less