  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.
