Calculations of Energetic Ions Energy Transfer via Slowing down Mechanism

Abstract

Fast ions in various toroidal devices, such as in tokamaks, play a vital role in bringing and sustaining a thermonuclear fusion process. They can transfer their (excessive) energy to the bulk plasma particles via various collisional processes, for example, the so-called slowing-down process. Here we have considered the slowing-down of energetic ions generated by neutral beam injection in a tokamak plasma has been studied. The kinetic theory of plasmas, which involves the time evolution of various species’ phase-space distribution function, has been employed. First, we have presented a detailed derivation of kinetic equations and introduced the concept of Fokker-Planck collisional effects. The injection of fast neutral atoms is the most exciting method for auxiliary heating, via the transfer of collisional energy from the fast ions formed in the limited orbits of the fusion plasmas’ plasma particles. Particles and energy losses due to charge exchange with the energy transferred to plasma ions, electrons, and background neutrals are calculated. Since the losses of energy transfer and charge exchange depend strictly on the neutral density and the electron temperature, the allowance of arbitrary profiles for n˙0=n˙e and T˙e and the fast ion accumulation are also included. The energy transferred to plasmas can be severely affected by charge exchange between fast ions and neutral background particles. Coulomb scattering is mainly used to find the velocity distribution of fast ion populations. The transport of high-speed ions is generally much slower than thermal transport, except during MHD events. Intensified populations of fast ions drive collective instabilities.