Nonlinear Development of the Beam-Cyclotron Instability

A theory is presented for the nonlinear evolution of the beam-cyclotron instability, together with the results of a series of computer experiments confirming the main points of the theory. We conclude that at a turbulent level which is proportional to ${\left(\frac{{\Omega }_{\mathrm{ce}}}{{\omega }_{\mathrm{pe}}}\right)}^2$, a transition is made to the nonmagnetic ion acoustic instability. For small $\frac{T_i}{T_e}$, the system then evolves until the fluctuating fields become strong enough to stabilize by ion trapping.