Long-Pulse Fast Ignition in MagLIF

TL;DR

This work addresses whether fast ignition (FI) can be made practically feasible withinMagLIF by leveraging its cylindrical geometry and axial magnetic fields to suppress energy losses and allow long, low-energy ignitor pulses. It develops a coupled hotspot-expansion and energy-dynamics framework that includes anisotropic Braginskii conduction, nonlocal transport via SNB-based flux limiting, PdV and bremsstrahlung losses, and electron-ion equilibration, then uses this model to estimate ignition-energy requirements. The results indicate FI is viable with long-pulse (≈100 ps) ignitors delivering as little as ~5 kJ for certain densities and hotspot sizes under $B_0\,=\,30$ kT, highlighting MagLIF’s potential to relax FI constraints relative to laser ICF. The study discusses practical implications for repetition rate, suggests magnetized guiding-cone strategies to further improve energy coupling, and outlines future directions to optimize hotspot geometry and magnetic-field configurations for high-yield, repeatable FI operation.

Abstract

The fast ignition paradigm for inertial confinement fusion (ICF) allows for extremely high gains but requires fuel to be heated very quickly to outpace hotspot disassembly and energy losses. This demands lasers with high power and intensity, posing engineering challenges that have called into question the fundamental practicality of fast ignition. Magnetized liner inertial fusion (MagLIF) circumvents these problems through its large-aspect-ratio cylindrical geometry and strong axial magnetic fields that allow for ignition at lower areal densities. Furthermore, MagLIF's large aspect ratio and higher yields relax other constraints on energy deposition and repetition rate while its axial magnetic fields can be used to collimate ignitor electrons and thereby increase allowed standoff distance and save on ignitor energy. This tremendous overall relaxation of the engineering constraints that have historically limited the practicality of fast ignition suggests that the paradigm may be considerably more viable in a MagLIF context.

Figures (14)

• Figure 1: The three regions in our model.
• Figure 2: Compression ratio vs. magnetic pressure for radial expansion ratio $x=1$ and cold fuel pressure $a=0$.
• Figure 3: Shock speed vs. magnetic pressure for radial expansion ratio $x=1$ and cold fuel pressure $a=0$. In order for the front to be a shock, it must travel faster than the sound (magnetosonic) speed in the cold fuel.
• Figure 4: Hotspot speed vs. magnetic pressure for radial expansion ratio $x=1$ and cold fuel pressure $a=0$.
• Figure 5: Hotspot speed vs. magnetic pressure for radial expansion ratio $x=1.75$ and cold fuel pressure $a=0$. Hotspot speed goes to zero when total pressure (thermal plus magnetic) in the hotspot equals total pressure in the cold fuel.