Control of laser-plasma instabilities in direct-drive ignition
In plain words
In direct drive the lasers shine straight on the capsule, which is more efficient, but the light also excites plasma waves that waste energy and make fast electrons that preheat the fuel. Whether these effects can be suppressed enough at full scale is unknown.
Precise statement
At ignition-scale direct drive (intensity about $1e22\,\mathrm{erg}\,\mathrm{s}^{-1}\,\mathrm{cm}^{-2}$), cross-beam energy transfer, two-plasmon decay and stimulated Raman scattering reduce absorption and produce hot electrons that preheat the fuel. Determine the absorbed fraction and the hot-electron preheat energy at full scale, and whether broadband or multi-color laser light suppresses them enough to allow $G$ above 10. An answer is a validated kinetic plus hydrodynamic prediction tested at intermediate scale.
What would settle it
Scaled experiments with broadband lasers that match predicted absorption and preheat, extrapolated by validated simulations.
Related problems
- Special case of Can laser-driven inertial fusion reach target gain of 10