Abstract
In inertial confinement fusion experiments at the National Ignition Facility, a spherical shell of deuterium–tritium fuel is imploded in an attempt to reach the conditions needed for fusion, self-heating, and eventual ignition. Since theory and simulations indicate that ignition efficacy in 1D improves with increasing imploded fuel convergence ratio, it is useful to understand the sensitivity of the scale-invariant fuel convergence on all measurable or inferable 1D parameters. In this paper, we develop a simple isobaric and isentropic compression scaling model incorporating sensitivity to the in-flight adiabat inferred from shock strengths, to measured implosion velocity, and to known initial ablator and fuel aspect ratio and mass ratio. The model is first benchmarked to 1D implosion simulations spanning a variety of relevant implosion designs. We then use the model to compare compressibility trends across all existing indirect-drive layered implosion data from the facility spanning three ablators [CH, carbon (C), and Be], for which in-flight fuel adiabats varied from 1.6 to 5 by varying the number of drive shocks from 2 to 4, peak implosion velocities varied by 1.4×, capsule radii by 50%, and initial fuel aspect ratios by 1.4×. We find that the strength of the first shock is the dominant contributor setting the maximum fuel convergence. We also observe additional sensitivities to successive shock strengths and fuel aspect ratios that improve the agreement between the expected and measured compression for carbon and Be designs with adiabats above 3. A principal finding is that the adiabat 2.5 C-shell designs exhibit less convergence than CH-shell designs of similar inferred in-flight adiabat.
Highlights
In inertial confinement fusion experiments at the National Ignition Facility, a spherical shell of deuterium–tritium fuel is imploded in an attempt to reach the conditions needed for fusion, self-heating, and eventual ignition
Since theory and simulations indicate that ignition efficacy in 1D improves with increasing imploded fuel convergence ratio, it is useful to understand the sensitivity of the scale-invariant fuel convergence on all measurable or inferable 1D parameters
We develop a simple isobaric and isentropic compression scaling model incorporating sensitivity to the in-flight adiabat inferred from shock strengths, to measured implosion velocity, and to known initial ablator and fuel aspect ratio and mass ratio
Summary
In inertial confinement fusion (ICF), a spherical shell of deuterium–tritium fuel (DT) of initial radius R0 and thickness DR0 is imploded to reach the conditions needed for fusion, self-heating, and eventual burn.[1]. A high stagnation hot spot areal density qHSRHS (0.2–0.3 g/cm2) and a high cold fuel areal density qDR (1–2 g/cm2) are needed so that the burn rate can exceed the disassembly rate In this model, the predicted DT neutron yield in the absence of alpha heating is. This paper serves to better quantify the basis for inferring fuel convergence, its sensitivities, constraints, trends, and relationships to the main 1D parameters of scale, initial fuel aspect ratio, velocity, and in-flight adiabat. We do this by first presenting a simple analytic model and benchmarking to 1D implosion simulations spanning a variety of relevant implosions designs. VIII, we summarize the trends and suggest some go-forward experimental design strategies
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