Possible nonlinear effects in electron-cyclotron plasma production and heating by microwave radiation are analyzed. They include nonlinear regimes of electron acceleration in strong microwave fields under cyclotron resonance conditions, nonstationary regimes of microwave beam self-focusing, and some parametric processes. Presented results may be of importance for predictions of plasma response to electron-cyclotron resonance (ECR) heating or preionization by powerful radiation.

When hydrogen is diffused into calcium fluoride crystals which contain a rare earth impurity and a relatively low concentration of oxygen two types of RE3--H-complexes of lower than axial symmetry are formed. These centres have been detected by measurements of the infrared absorption .from the localized vibrations of the paired H-(or D-) ions. In crystals containing Ce3+ ions, a new EPR spectrum has been observed which correlates with one of these centres. Models for the centres are discussed. and it is suggested that one may be a simple,modification of the trigonal (T,) centre R E 3 -0 2 -F ; , where one of the Fions is replaced by an Hion.

Absorption of microwave energy at electron-cyclotron frequency is a promising method of heating plasma to thermonuclear temperatures in large toroidal devices in which the energy confinement time exceeds the characteristic time of energy exchange between the electron and ion components of the plasma. The smallness of the wavelength compared with the dimensions of the system makes it possible to use quasioptical waveguides which are easy to match with the plasma. The microwave power, injected in the form of an ordinary wave from the outer part of the torus in the direction of increase of the toroidal component of the magnetic field, is efficiently absorbed if the dimensions of the tokamak are greater than or of the order of those of the T-10 device and the initial temperature of the plasma is greater than 1 keV. In the quasi-continuous heating regime and with reasonable microwave beam cross-sections non-linear effects have no appreciable effect on the cyclotron heating efficiency.

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