[en] Thermal conditions of foil of axial-symmetrical window for electron accelerator for two current density distributions in a beam were determined. Limiting frequences for different thermal conditions in foil were determined as well as pulse duration value τ at which temperature is proportional to τ. Expressions unambigously determining limiting beam current, which with chosen beam energy and its diameter in foil cross section can be passed through a window with thicknss h, with chosen beam energy and its diameter in foil cross section, were obtained. It is possible to increase limiting power passed through foil varying beam parameters and outlet window structure within permissible limits. Dependences obtained permit to choose the most suitable foil and cooling method. Titanium foil is preferable to use on intensive cooling with air, aluminium - in a pulsed regime of foil heating and on cooling with thermal conduction