Ion distribution functions during ion cyclotron resonance heating at the fundamental frequency

The distribution function of ions during ion cyclotron resonance heating (ICRH) is studied analytically using a simplified one-dimensional Fokker–Planck equation incorporating ion–ion and ion–electron collisions and rf quasilinear diffusion. By including source and loss terms in the equation, steady-state and time-dependent solutions, which are regular near the origin and vanish at high energies, are found. It is shown that an initially Maxwellian distribution function is transformed by the ICRH into a non-Maxwellian distribution with a tail of energetic ions. The tail is more pronounced when quasilinear diffusion dominates over collisions and losses.