Effects of alpha stopping power modelling on the ignition threshold in a directly-driven Inertial Confinement Fusion capsule

TL;DR

This study investigates how different alpha stopping power models affect ignition thresholds in direct-drive Inertial Confinement Fusion, revealing that the choice of model influences the energy required for ignition.

Contribution

It introduces a Monte-Carlo based alpha energy transport calculation into hydrodynamic simulations and compares LP and BPS stopping power models near ignition conditions.

Findings

BPS model requires about 10% more energy than LP model for same fusion output.

The choice of stopping power model impacts the ignition threshold.

Simulations map the transition between marginal ignition and high gain.

Abstract

The alpha-particle energy deposition mechanism modifies the ignition conditions of the thermonuclear Deuterium-Tritium fusion reactions, and constitutes a key issue in achieving high gain in Inertial Confinement Fusion implosions. One-dimensional hydrodynamic calculations have been performed with the code Multi-IFE [R. Ramis and J. Meyer-ter-Vehn, Comp. Phys. Comm. 203, 226 (2016)] to simulate the implosion of a capsule directly irradiated by a laser beam. The diffusion approximation for the alpha energy deposition has been used to optimize three laser profiles corresponding to different implosion velocities. A Monte-Carlo package has been included in Multi-IFE to calculate the alpha energy transport, and in this case the energy deposition uses both the LP [C.K. Li and R.D. Petrasso, Phys. Rev. Lett. 70, 3059 (1993)] and the BPS [L.S. Brown, D.L. Preston, and R.L. Singleton Jr., Phys. Rep. 410, 237 (2005)] stopping power models. Homothetic transformations that maintain a constant implosion velocity have been used to map out the transition region between marginally-igniting and high-gain configurations. The results provided by the two models have been compared and it is found that - close to the ignition threshold - in order to produce the same fusion energy, the calculations performed with the BPS model require about 10% more invested energy with respect to the LP model.