where i is wavelength of the probe radiation; 8 is the scattering angle; k D = (Te/4~nee2) I/2 is the Debye radius; ne, T e are the electron concentration and temperature; e is the charge of the electron. For e > i corresponds to collective radiation scattering, and analysis of its spectrum allows the ion temperature to be measured, independently of electron concentration, and plasma oscillations and instabilities to be studied. As is evident from the expression for ~, using lasers for diagnostics in the visibie and IR regions of hot plasma (T e -~ 1 KeV) with moderate density (n e = 10• cm -3) collective processes can only be observed with small scattering angles, which prevents localized measurements and makes the detection of useful signals difficult. Switching to a laser in the submiiiimeter (SVIM) region allows operation at angles up to ~/2 (which significantly increases spatial resolution) and allows heterodyne methods of detection to be used. Furthermore, the scattered power is proportional to the square of the wavelength of the probe radication, whch eases detection.