  The state of burning plasma had been achieved in inertial confinement fusion
(ICF), which was regarded as a great milestone for high-gain laser fusion
energy. In the burning plasma, alpha particles incident on the cryogenic (warm
dense) fuels cannot be simply regarded as single particles, and the new physics
brought about by the density effects of alpha particles should be considered.
In this work, the collective interaction between them has been considered,
namely the effect of the superposition of wake waves. The stopping power of
alpha-particle clusters, i.e. the rate of energy loss per unit distance
traveled has been calculated using both analytical and simulation approaches.
In theory, we obtain the stopping power of alpha clusters in cryogenic (warm
dense) fuel by the dielectric function method, which illustrates the importance
of the effective interaction between particles. Simulation results using the
LAPINS code show that the collective stopping power of the alpha cluster is
indeed increased via coherent superposition of excitation fields (the
excitation of high-amplitude wake waves). However, the comparison between
simulation and theoretical results also illustrates a coherent-decoherent
transition of the stopping power of the cluster. The initial conditions with
various sizes and densities of the alpha clusters have been considered to
verify the condition of decoherence transition. Our work provides a theoretical
description of the transport properties of high-density alpha particles in warm
dense cryogenic fuel and might give some theoretical guidance for the design of
actual fusion processes.
