Simulation studies of heavy ion heating by current-driven instabilities

Nonlinear evolution of current-driven instabilities and associated energy t ransport among different particle species are studied by means of a two-dim ensional, electrostatic, particle simulation code with full ion and electro n dynamics. The plasma is assumed to consist of hydrogen (H) and helium (He ) ions and electrons with the electron temperature larger than the ion temp eratures; the electrons drift along a uniform magnetic field with an initia l speed equal to the thermal speed. Then, simulations show that after the d evelopment of ion acoustic waves and fundamental H cyclotron waves, second harmonic waves are destabilized due to the change in the electron velocity distribution function parallel to the magnetic field, f(e)(upsilon (paralle l to)). Even though the linear theory based on the initial conditions predi cts that the second harmonics are only marginally unstable, they eventually grow to the largest amplitudes and heat He ions more significantly than H ions. The instabilities of these three kinds of modes with different phase velocities give rise to flattening of f(e)(nu (parallel to)) over a region larger than the thermal speed. (C) 2000 American Institute of Physics. [S10 70-664X(00)03612-0].