A heating mechanism of electron plasmas by high-power microwaves in a magnetic mirror is investigated theoretically, with reference to experiments in a device named TP-M. The heating is assumed to be due to a microwave mode propagating perpendicular to the magnetic field since higher harmonic resonances, the main features of the experiments, exist. The heating mechanism can be interpreted in terms of a stochastic process, a random walk in velocity space.It is confirmed numerically that localized resonance zones of finite width exist, the electrons are effectively heated only in the resonance zones, and that the presence of a randomization process of the relative phase relation between the wave and the electron gyration is essential for the heating process. On the basis of the numerical analysis, the heating process is treated analytically. The electrons are assumed to pass the resonance zones repeatedly in the course of oscillatory motions between turning points, and the relative phase relation is assumed to be random at each passage through the resonance zone. The heating rate is calculated and found to agree with the experimental value. The causes of phase randomization, the effects of the loss cone and the observed saturation of electron temperature are also discussed.
Microwave heating rates for a plasma in a d.c. magnetic field as determined from inverse synchrotron emission