Kinetic effects on alpha particle energy transfer in dense core plasma

Efficient creation of burning plasmas is a central issue of fusion energy science. In laser fusion, the burning starts from a hot spot where non-thermal alpha particles are created by DT fusion reactions. The alpha particles transfer their energies to bulk plasma particles, and the hot bulk region extends. The average timescale of the energy transfer by collisions is estimated for thermally distributed bulk plasma particles. However, recent NIF experiments suggested the ions have a non-thermal distribution in the fusion plasma. This infers that the kinetic description is important to understand the burning plasma dynamics. In this study, Monte-Carlo calculations of binary collisions [1] show that non-thermal energy tails appear in energy distributions of DT ions in the relaxation process of alpha particles. We found that the alpha particle energy is converted quickly to deuterons in the non-thermal tail and energetic deuterons are generated with velocities close to the alpha particle velocities. The energies of the fast deuterons are enough high for successive fusion reactions. We model this kinetic processes and derive the condition to initiate the efficient energy transfer to plasma ions. [1] Y. Sentoku and A. J. Kemp, J. Comput. Phys. 227, 6846 (2008).