Integrated Radiation-Magneto-Hydrodynamic Simulations of Magnetized Burning Plasmas. I. Magnetizing Ignition-Class Designs

TL;DR

This work uses fully integrated 2D rad-MHD simulations with the Lasnex Hohlraum Template to quantify how imposed axial magnetic fields influence hohlraum-driven ignition-class ICF designs. By tuning unmagnetized baselines to NIF data and applying fields across five designs (N180128, N210808, N221204, EYC, and PSS), the study demonstrates that moderate magnetization can substantially boost yield and hotspot temperature, primarily through reduced electron heat conduction and enhanced alpha deposition, while field strength and design asymmetries govern the magnitude of improvement. Across the three historical high-performing shots, magnetization yields typical increases of $2 imes$ with notable enhancements up to $6$–$8 imes$ at higher fields for certain configurations; the PSS design shows particularly strong gains (up to ~$12.5 imes$ in some cases and even at very low fields), whereas the 3 MJ EYC design exhibits limited benefits from magnetization, highlighting the need for design-tailored magnetic fields. The results indicate magnetization is a viable route to improve ignition-class ICF performance, motivate magnetic-profile optimization and ice-layer shaping, and motivate a targeted Part II to study extended MHD effects and more sophisticated design strategies for magnetized ICF.

Abstract

Motivated by breakthroughs in inertial confinement fusion (ICF), first achieving ignition conditions in National Ignition Facility (NIF) shot N210808 and then laser energy breakeven in N221204, modeling efforts here investigate the effect of imposed magnetic fields on integrated hohlraum simulations of igniting systems. Previous NIF experiments have shown yield and hotspot temperature to increase in magnetized, gas-filled capsules in line with scalings. In this work, we use the 2D radiation-magnetohydrodynamics code Lasnex with a Livermore ICF common model. Simulations are tuned to closely approximate data from unmagnetized experiments. Investigated here is the effect of imposed axial fields of up to 100 T on the fusion output of high-performing ICF shots, specifically the record BigFoot shot N180128, and HYBRID-E shots N210808 and N221204. The main observed effect is an increase in the hotspot temperature due to magnetic insulation. Namely, electron heat flow is constrained perpendicular to the magnetic field and alpha trajectories transition to gyro-orbits, enhancing energy deposition. In addition, we investigate the impact of applied magnetic fields to future NIF designs, specifically an example Enhanced Yield Capability design with 3 MJ of laser energy as well as a high-\r{ho}R, low implosion velocity "Pushered Single Shell" design. In conclusion, magnetization with field strengths of 5-75 T is found to increase the burn-averaged ion temperature by 50% and the neutron yield by 2-12. Specifically, we see yield enhancement of at least 50% with only a 5-10 T applied magnetic field for N221204, while a 65 T field on N210808 with symmetrization gives an 8 increase in yield. This is all without further design optimization to best take advantage of an applied B field, which promises even greater improvements for designs tailored specifically towards magnetization.

Figures (20)

• Figure 1: Example visualizations of the (a) hohlraum, (b) HDC capsule, and (c) PSS capsule parametrization used in this study.
• Figure 2: Comparison of (a) the laser drive profiles and (b) the corresponding $T_\text{rad}$ profiles predicted by the simulations for N180128 (blue), N210808 (orange), N221204 (green), EYC (purple), and PSS (red). N180128 is a BigFoot design while N210808, N221204, and EYC are all HYBRID-E. The rapid rise in $T_{rad}$ late in time for the HYBRID-E shots is posited to be due to reheating of the hohlraum wall by the high yields generated. This reheating was observed in N221204 but the appropriate diagnostic was not available for N210808.
• Figure 3: Plot of density $\rho$ [g/cm$^{3}$] for N210808 when (a) unsymmetrized and (b) symmetrized. Polar caps as seen in a) are standard features in current ICF designs, i.e., HYBRID-E.
• Figure 4: A comparison of the $T_{rad}^4 \propto p_0$ in (a)-(e), $p_2/p_0$ in (f)-(j), and $p_4/p_0$ in (k)-(o) Legendre modes of the x-ray drive at varying magnetic field strengths for the shots in question.
• Figure 5: Comparison of yields (blue) and $\textit{T}_\text{ion}$ (red) for the five NIF designs when an external magnetic field is applied (two instances for PSS). In addition, we consider the fully-integrated, asymmetric implosion (solid) and compare it to the symmetrized results (dashed). Stars mark the baseline, unmagnetized result when symmetrized and mix is not enabled, which is effectively the idealized 1D limit. Slight mix can actually enhance performance in certain conditions but is beyond our capabilities to control as of now. Plotted here are results for a) N180128, b) N210808, c) N221204, d) PSS with moderate mix ($\delta h = 0.25 \mu m, f_\text{mix}=0.02 \%$), e) PSS with low mix ($\delta h = 0.2 \mu m, f_\text{mix}=0.015 \%$), and f) EYC. The numbers in the top-right corner of each panel denote the normalization value for each panel with respect to $Y$ and $\textit{T}_\text{ion}$ .