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Abstract
The yield of an inertial confinement fusion capsule can be greatly affected by the inclusion of highZ material in the fuel, either intentionally as a diagnostic or from mixing due to hydrodynamic instabilities. To validate calculations of these conditions, glass shell targets filled with a D_{2} and ^{3}He fuel mixture were fielded in experiments with controlled amounts of premixed Ar, Kr, or Xe. The experiments were fielded at the OMEGA laser [T. R. Boehly et al., Opt. Commun. 133, 495 (1997)] using 1.0 ns square laser pulses having a total energy 23 kJ and direct drive illumination of shells with an outer diameter of ∼925 μm and a thickness of ∼5 μm. Data were collected and compared to onedimensional integrated models for yield and burntemperature measurements. This paper presents a critical examination of the calculational assumptions used in our experimental modeling. A modified treatment of lasercapsule interaction improves the match to the measured scattered laser light and also improves agreement for yields, burntemperatures, and the fuel compression as measured by the ratio of two yields. Remaining discrepancies between measurement and calculation will also be discussed.
The authors would like to acknowledge useful conversations with Nelson Hoffman and Manolo Sherrill. The authors also wish to thank the staff at LLE who run the OMEGA laser facility and the staff of General Atomics who fabricated the targets. This work was supported by the U.S. Department of Energy, and operated by Los Alamos National Security LLC under Contract Nos. DEAC5206NA25396 and LAUR1105291.
I. INTRODUCTION
II. EXPERIMENTAL SETUP
III. CALCULATION SETUP
IV. PARAMETER STUDY
V. CALCULATIONS
VI. DISCUSSION AND SUMMARY
Key Topics
 Neutrons
 19.0
 Hydrological modeling
 11.0
 Light scattering
 11.0
 Hydrodynamics
 9.0
 Inertial confinement
 9.0
Figures
The capsules used were SiO_{2} shells with a typical outer diameter of 925 ± 15 μm, a thickness of 5.0 ± 0.5 μm, and an average density of 2.2 g/cm^{3}. They were filled with a fuel mixture, which typically included 6.7 atm of deuterium and 3.3 atm of ^{3}He. The base target was varied by including a known amount of a premixed Kr gas in the fuel in the amounts of 0.00 atm (base), 0.01 atm, 0.05 atm, and 0.75 atm.
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The capsules used were SiO_{2} shells with a typical outer diameter of 925 ± 15 μm, a thickness of 5.0 ± 0.5 μm, and an average density of 2.2 g/cm^{3}. They were filled with a fuel mixture, which typically included 6.7 atm of deuterium and 3.3 atm of ^{3}He. The base target was varied by including a known amount of a premixed Kr gas in the fuel in the amounts of 0.00 atm (base), 0.01 atm, 0.05 atm, and 0.75 atm.
The amount of premix needed to reduce the yield by 50% has been measured and plotted as a function of atomic number, Z, for the data described in Ref. 4. The data include premixed He, Ar, Kr, and Xe and show that the yield reduction threshold scales as f(Z) ∼ Z ^{−2}.
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The amount of premix needed to reduce the yield by 50% has been measured and plotted as a function of atomic number, Z, for the data described in Ref. 4. The data include premixed He, Ar, Kr, and Xe and show that the yield reduction threshold scales as f(Z) ∼ Z ^{−2}.
Data from OMEGA shot 50 997 are shown for the timedependent incident power (blue solid line), scattered power (solid black line), and the difference of these two signals (dashed blue line). This difference is the measurement of the laser absorption. For shot 50 997, the measured fraction of total incident energy to absorbed energy was ∼60%, while ∼80% was calculated when the full laser power was initially used in the calculation.
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Data from OMEGA shot 50 997 are shown for the timedependent incident power (blue solid line), scattered power (solid black line), and the difference of these two signals (dashed blue line). This difference is the measurement of the laser absorption. For shot 50 997, the measured fraction of total incident energy to absorbed energy was ∼60%, while ∼80% was calculated when the full laser power was initially used in the calculation.
Examples are plotted from the twoparameter scan of shot 51 483. (a) shows the case for a yield, Y _{ DDn }, and (b) the time where the neutron rate equals 10^{−2} times the peak rate (T_{start}) and is approximately when the shock reflects from the center of the target. The colors, as shown in the color bar, represent the calculated quantity. Overplotted is a white contour line, which is the set of points where the synthetic quantity agrees with experimental measurement.
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Examples are plotted from the twoparameter scan of shot 51 483. (a) shows the case for a yield, Y _{ DDn }, and (b) the time where the neutron rate equals 10^{−2} times the peak rate (T_{start}) and is approximately when the shock reflects from the center of the target. The colors, as shown in the color bar, represent the calculated quantity. Overplotted is a white contour line, which is the set of points where the synthetic quantity agrees with experimental measurement.
The six measured quantities (contours) for shot 50 997 shown are as follows: the ion burntemperature (cyan solid line); neutron bang time (black solid line); the total absorbed laser energy (solid green line); and the three particle yields Y _{ DDn } (solid blue line), Y _{ DTn } (dashed blue line), and Y _{ D3Hep } (red dashed line). Any measured quantity can be matched in a calculation by picking a point, (f _{ e }, m), along the appropriate contour. The large dots mark the multipliers used for the old (black) and new (green) calculations and are discussed in more detail in the text.
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The six measured quantities (contours) for shot 50 997 shown are as follows: the ion burntemperature (cyan solid line); neutron bang time (black solid line); the total absorbed laser energy (solid green line); and the three particle yields Y _{ DDn } (solid blue line), Y _{ DTn } (dashed blue line), and Y _{ D3Hep } (red dashed line). Any measured quantity can be matched in a calculation by picking a point, (f _{ e }, m), along the appropriate contour. The large dots mark the multipliers used for the old (black) and new (green) calculations and are discussed in more detail in the text.
The neutron yield Y _{ DDn } is plotted as a function of Krfraction in the fuel for three sets of points: the experimentally measured yields (black circles), the previous calculations (green triangles), and the new calculations (blue diamonds). There is an overlap between the three sets of points for Krfractions of 0.0 and ∼0.001 (n.b. the xaxis is logarithmic and a 0.0 Krfraction has been offset to 0.0001).
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The neutron yield Y _{ DDn } is plotted as a function of Krfraction in the fuel for three sets of points: the experimentally measured yields (black circles), the previous calculations (green triangles), and the new calculations (blue diamonds). There is an overlap between the three sets of points for Krfractions of 0.0 and ∼0.001 (n.b. the xaxis is logarithmic and a 0.0 Krfraction has been offset to 0.0001).
The ratio, Y _{ DDn }/Y _{ DTn }, is plotted as a function of the fuel Krfraction for the same three sets of data and simulations in Fig. 6. The ratio used in this plot, Y _{ DDn }/Y _{ DTn }, increases with decreasing ρR, and thus less compressed capsules appear towards the top of the plot and more compressed capsules near the bottom.
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The ratio, Y _{ DDn }/Y _{ DTn }, is plotted as a function of the fuel Krfraction for the same three sets of data and simulations in Fig. 6. The ratio used in this plot, Y _{ DDn }/Y _{ DTn }, increases with decreasing ρR, and thus less compressed capsules appear towards the top of the plot and more compressed capsules near the bottom.
The burnweighted iontemperature is shown for the same set of data and simulations as in Figs. 6 and 7. At the highest Krfraction level of 0.04, the original calculated temperatures were substantially different from the measurements in Ref. 4.
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The burnweighted iontemperature is shown for the same set of data and simulations as in Figs. 6 and 7. At the highest Krfraction level of 0.04, the original calculated temperatures were substantially different from the measurements in Ref. 4.
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Abstract
The yield of an inertial confinement fusion capsule can be greatly affected by the inclusion of highZ material in the fuel, either intentionally as a diagnostic or from mixing due to hydrodynamic instabilities. To validate calculations of these conditions, glass shell targets filled with a D_{2} and ^{3}He fuel mixture were fielded in experiments with controlled amounts of premixed Ar, Kr, or Xe. The experiments were fielded at the OMEGA laser [T. R. Boehly et al., Opt. Commun. 133, 495 (1997)] using 1.0 ns square laser pulses having a total energy 23 kJ and direct drive illumination of shells with an outer diameter of ∼925 μm and a thickness of ∼5 μm. Data were collected and compared to onedimensional integrated models for yield and burntemperature measurements. This paper presents a critical examination of the calculational assumptions used in our experimental modeling. A modified treatment of lasercapsule interaction improves the match to the measured scattered laser light and also improves agreement for yields, burntemperatures, and the fuel compression as measured by the ratio of two yields. Remaining discrepancies between measurement and calculation will also be discussed.
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