Resonance density range governs two-plasmon decay saturation and enables hot-electron prediction in inertial confinement fusion

The saturation level of parametric instabilities is critical in determining their impact on fusion plasmas. We identify the resonance density range of two-plasmon decay as the critical parameter governing nonlinear saturation of ion density fluctuations and Langmuir waves, which drive hot-electron generation. Using this insight, we develop a predictive scaling model for the hot-electron energy fraction fhot that depends only on the laser intensity I0, with plasma conditions encoded via plasma ablation theory. The model can work for various experimental configurations—requiring only two or three (I0, fhot) data points to calibrate coefficients when properly chosen—and successfully reproduces results from prior OMEGA, OMEGA-EP, and SG-II experiments.