Engineering topics

Graziani, F. (ORCID:0000000272040509)

Publications and source records attributed to Graziani, F. (ORCID:0000000272040509).

3 records

DOE OSTI2024

Effects of drive pulse shape on graded metal pushered single shell capsule implosions on the National Ignition Facility

Graded metal pushered single shells (PSS) are a viable alternative to low-Z capsules (Z is the atomic number) for indirect drive inertial confinement fusion implosions due to enhanced core tamping and radiation trapping, but they can be compromised by the pusher mixing with the fuel. We compare 2-shock and 3-shock laser pulses for Be/Cr PSS capsules filled with deuterium–tritium gas fuel at 6 mg/cc density. 1D radiation-hydrodynamic simulations predict higher core compression and, hence, ∼2× higher fusion yield for the 3-shock drive than for 2-shock. Nevertheless, we observe similar core ion temperatures and fusion yields for both drives. The implosion burn duration is 25% shorter and the core volume is ∼2.5× smaller for the 3-shock drive than for 2-shock, consistent with a higher compression. 1D LASNEX mix simulations using a buoyancy-drag model matching the measured yields also agree with the observed core sizes and burn durations and suggest ∼40% and ∼70% yield degradations for 2-shock and 3-shock drives due to hydrodynamic instabilities and atomic mix at the pusher–fuel interface. At the same time, 2D HYDRA simulations show that mid-mode (2–250) instability degradations are negligible for the 2-shock implosion (9%) and significant (45%) for 3-shock. Subtracting these from the 1D mix simulations, we infer similar degradations from high-mode instabilities and atomic mix for both drives. Due to its robustness to mid-mode instabilities, future pusher–gas mix studies will use the 2-shock drive.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗

DOE OSTI2023

First bromine doped cryogenic implosion at the National Ignition Facility

We report on the first experiment dedicated to the study of nuclear reactions on dopants in a cryogenic capsule at the National Ignition Facility (NIF). This was accomplished using bromine doping in the inner layers of the CH ablator of a capsule identical to that used in the NIF shot N140520. The capsule was doped with 3 × 1016 bromine atoms. The doped capsule shot, N170730, resulted in a DT yield that was 2.6 times lower than the undoped equivalent. The Radiochemical Analysis of Gaseous Samples (RAGS) system was used to collect and detect 79Kr atoms resulting from energetic deuteron and proton ion reactions on 79Br. RAGS was also used to detect 13N produced dominantly by knock-on deuteron reactions on the 12C in the ablator. High-energy reaction-in-flight neutrons were detected via the 209Bi(n,4n)206Bi reaction, using bismuth activation foils located 50 cm outside of the target capsule. The robustness of the RAGS signals suggests that the use of nuclear reactions on dopants as diagnostics is quite feasible.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗

DOE OSTI2020

Symmetry tuning and high energy coupling for an Al capsule in a Au rugby hohlraum on NIF

Experiments on imploding an Al capsule in a Au rugby hohlraum with up to a 1.5 MJ laser drive were performed on the National Ignition Facility (NIF). The capsule diameter was 3.0 mm with ∼1 MJ drive and 3.4 mm with ∼1.5 MJ drive. Effective symmetry tuning by modifying the rugby hohlraum shape was demonstrated, and good shell symmetry was achieved for 3.4 mm capsules at a convergence of ∼10. The nuclear bang time and the shell velocity from simulations agree with experimental data, indicating ∼500 kJ coupling with 1.5 MJ drive or ∼30% efficiency. The peak velocity reached above 300 km/s for a 120 μm-thick Al capsule. The laser backscatter inside the low-gas-filled rugby hohlraum was very low (<4%) at both scales. The high energy coupling allows implosion designs with increased adiabat, which, in turn, increases the tolerance to detrimental effects of instabilities and asymmetries. These encouraging experimental results open new opportunities for both the mainline single-shell scheme and the double-shell design toward ignition.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗