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Shock ignition target design for inertial fusion energy
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Image of FIG. 1.
FIG. 1.

The 1D gain curve constructed from the optimum gain cases at each scale factor for the shock ignition targets simulated in this study.

Image of FIG. 2.
FIG. 2.

(a) Optimum gain, (b) peak laser intensities, and (c) laser pulse energies as a function of compression power, for a 250 ps FWHM ignitor and the scale-2 target.

Image of FIG. 3.
FIG. 3.

Comparison of simulation and predicted hot-spot (open diamonds) and cold-fuel (solid squares) energies. The predicted energies use the formula from Table II in Appendix A, and the assembled fuel masses, stagnation adiabats, and hot-to-cold pressure ratios measured in the simulations.

Image of FIG. 4.
FIG. 4.

Absorption and coupling efficiencies for the laser pulse to the pellet ignition assembly. The coupling efficiencies have the absorption factored out, i.e., they denote coupling of absorbed energies. The diamond symbols denote the laser compression pulse, and the square symbols denote ignitor pulse coupling.

Image of FIG. 5.
FIG. 5.

The ignitor shock pressures as a function of time, as the ignitor pulse width changes. The ignitor peak power is 450 TW. The solid lines are the peak shock pressures, while the dotted lines are the pressure at the laser critical surface. Inset: The pellet yield (diamond) and gain (triangle) vary with the ignitor pulse width.

Image of FIG. 6.
FIG. 6.

The gain vs ignitor timing and power (and pulse length) holding the ignitor energy fixed at 90 kJ.

Image of FIG. 7.
FIG. 7.

The maximum laser intensities and gains for scale-2 pellets rescaled to different initial aspect ratios. All targets have the same laser energy and implosion velocity (without ignitor).

Image of FIG. 8.
FIG. 8.

Relative rms perturbation of the areal mass in the pellet for the scale-2 target with a 300 kJ, 110 TW compression pulse. The solid black line shows the growth of outer surface perturbations (initially rms), the dash-dotted line is the inner surface perturbation (initially rms), the dashed line is for 300 overlapped 1 THz bandwidth ISI beams, all for a 150 kJ ignitor. The light solid line is for all three perturbation sources simultaneously and with a 200 kJ ignitor. The vertical gray lines denote the times (a) as the compression shock breaks out of the rear of the fuel shell; (b) as the ignitor shock turns on; and (c) when the pellet stagnates and ignition occurs.

Image of FIG. 9.
FIG. 9.

The areal mass perturbation amplitude spectrum, normalized to the average areal mass at four times during the implosion, for the different perturbations sources included here. The different times shown are at (a) ; (b) 12.8 ns when the shocks break out from the rear of the target; (c) 16 ns, when the ignitor shock turns on; and (d) 16.9 ns, when the pellet ignites. The sources included are perturbation on the outer surface (black), inner surface (dash-dotted), ISI laser imprint (dashed), and all three sources combined at once (gray). The modes greater than have been locally averaged in wavenumber from to to reduce statistical fluctuations that obscure the plot.

Image of FIG. 10.
FIG. 10.

Images of an imploding pellet at times (a) 100 ps after the ignitor starts; (b) as the ignitor shock is halfway through the shell; and (c) at stagnation as the burn begins. The pellet is initially perturbed on the outer and inner surfaces with “NIF-spec” spectra (Ref. 4) with nominal amplitudes of 0.48 and , respectively, and was subject to laser imprinting from 300 overlapped mutually incoherent 1 THz ISI beams. The resulting gain is 102.

Image of FIG. 11.
FIG. 11.

Low-mode simulations for target with two different convergence ratios. The perturbation amplitude is measured as a ratio to the nominal perturbation level ( rms in the wetted foam). Solid lines are the laser energy used at the optimal gain (left axis), while the dotted lines give the optimal gain (right axis).

Image of FIG. 12.
FIG. 12.

Growth of outer surface modes from high-resolution simulations comparing the original lower AR target with a target that is designed for about 40% lower drive pressure . The cross marks on the curves denote the time of ignitor turn-on and ignition.

Image of FIG. 13.
FIG. 13.

Images of the imploded density just as the pellet begins to burn (gain is at these times) for (a) lower AR target and (b) a higher AR target .

Image of FIG. 14.
FIG. 14.

For the isobaric pellet assembly , the total and component energies of the pellet assembly as a function of assembly pressure. The fuel assembly gain (gray curve, with axis at right) is also shown. Note that the peak gain occurs at a pressure that is greater than that at the point of minimum total energy.

Image of FIG. 15.
FIG. 15.

The function describes the sensitivity of the core radius to initial mass perturbations, whereas the function (in gray) describes the sensitivity of the final target mass to pressure perturbations.


Generic image for table
Table I.

Target specifications listed by relative mass. In all cases, the ablator is made of CH foam wicked with solid DT and the fuel layer is DT ice. The target linear dimensions are scaled by the cube root of the scale factor, which denotes the relative target mass. Simulation parameters listed are those found at highest gain.

Generic image for table
Table II.

Fuel assembly parameters at peak gain, expressed as a function of mass .

Generic image for table
Table III.

Fuel assembly parameters at peak gain in terms of total energy.


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752b84549af89a08dbdd7fdb8b9568b5 journal.articlezxybnytfddd
Scitation: Shock ignition target design for inertial fusion energy