Nonlinear absorption of intense microwave pulses

Free-electron lasers in the electron cyclotron frequency range have been proposed as an efficient means of heating and driving current in tokamak plasmas. The proposed free-electron laser will have short pulses ({}5×{}10^-8 sec) with a peak power of (4--8)×{}10⁹ W and electric fields within the plasma in the range 10⁵--10⁶ V/cm. At these high intensities nonlinear effects compete with thermal effects in the absorption of microwave power. Analytic and numerical calculations of the nonlinear absorption are presented.