Аннотация:The results of theoretical analysis of electron beam optics system and interaction region of the high power W-band extended interaction klystron with hollow electron beam are prezented. The computer code PARS is used for numerical simulation. As result of optimization, the design of extended interaction klystron with 6 maltigap cavities has been developed. The klystron provides output power about 8.6 kW with 56 dB gain, 32% electronic efficiency and 40% total efficiency with depressed collector. Developed double-stage depressed collector shows beam energy recovery efficiency 54% in dynamic regime with taking into account of secondary electron emission from collector’s walls.