The interpretation of experimental data on characterictics of radiation fields during the physical start-up of the T-15 tokamak is given; the consistency of results obtained at the T-10, JET, TFTR, T-15 tokamaks is shown. Possible ways of formation of accelerated electron beam and a number of models of radiation field formation in such operating conditions are discussed. Methods for the diagnostics of electron beam characteristics by synchrotron radiation and by the analysis of bremsstrahlung pulse shape are suggested; the prediction of radiation situation for T-15 depending on a quantity of regimes with accelerated electrons is presented. 25 refs.; 26 figs.; 3 tabs.