Ion Heating via Turbulent Ion Acoustic Waves

Three-dimensional ion acoustic turbulence is excited by injecting a cold ion beam into a nonmagnetized plasma with TₑTᵢ>5. A rapid, approximately exponential heating of the ion beam is observed along the beam path. The heating rates level off when the ion temperature approaches 0.2Tₑ. The turbulent ion acoustic wave energy density does not exceed (1-3)×10^-3Tₑ. Wave saturation, which occurs before significant dissipation of ion beam energy, is consistent with orbit-diffusion strong-turbulence theory.