Abstract
The first hydrodynamic instability growth measurements with three-dimensional (3D) surface-roughness modulations were performed on CH shell spherical implosions at the National Ignition Facility (NIF) [G. H. Miller, E. I. Moses, and C. R. Wuest, Opt. Eng. 43, 2841 (2004)]. The initial capsule outer-surface amplitudes were increased approximately four times, compared with the standard specifications, to increase the signal-to-noise ratio, helping to qualify a technique for measuring small 3D modulations. The instability growth measurements were performed using x-ray through-foil radiography based on time-resolved pinhole imaging. Averaging over 15 similar images significantly increased the signal-to-noise ratio, making possible a comparison with 3D simulations. At a convergence ratio of ${\sim}2.4$ , the measured modulation levels were ${\sim}3$ times larger than those simulated based on the growth of the known imposed initial surface modulations. Several hypotheses are discussed, including increased instability growth due to modulations of the oxygen content in the bulk of the capsule. Future experiments will be focused on measurements with standard 3D ‘native-roughness’ capsules as well as with deliberately imposed oxygen modulations.
Highlights
The goal of inertial confinement fusion (ICF)[1,2,3] is to implode a spherical target to achieve high compression of a cryogenic deuterium–tritium (DT) fuel layer and high temperature in the central hot spot to trigger ignition and produce significant thermonuclear energy gain
In recent high-compression experiments at the National Ignition Facility (NIF)[4], the highest fuel areal densities (ρ R) were achieved in implosions with ignitionrelevant implosion velocities[5, 6]. These key performance parameters were close to the goal of the ignition point design[7], but the neutron yields were significantly reduced from expectations[5, 6]
The measured peak modulation level at a spatial frequency of ∼20 mm−1 is approximately three times higher than the peak of the simulated spectrum. This discrepancy may be a very important clue in improving our understanding of the performance of layered DT implosions conducted during the National Ignition Campaign (NIC)[6,7,8]
Summary
The goal of inertial confinement fusion (ICF)[1,2,3] is to implode a spherical target to achieve high compression of a cryogenic deuterium–tritium (DT) fuel layer and high temperature in the central hot spot to trigger ignition and produce significant thermonuclear energy gain. In recent high-compression experiments at the National Ignition Facility (NIF)[4], the highest fuel areal densities (ρ R) were achieved in implosions with ignitionrelevant implosion velocities[5, 6]. These key performance parameters were close to the goal of the ignition point design[7], but the neutron yields were significantly reduced from expectations[5, 6].
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