Introduction 777 Problems of High-power Electronics 778 I. Solution of the Fundamental Equation of Motion of Charged Particles by the Time- Averaging Method 780 II. Motion of Electrons in a Planotron 784 III. Principal Characteristics of the Planotron 788 IV. Anode and Cathode Losses in the Planotron, 794 V. Edge Effect and Associated Losses 798 VI. Theory of the Magnetron 804 VII. Experimental Investigation of the Electronic Processes in the Planotron 811 VIII. Larmor Orbit in High-frequency Field 817 IX. Prospects of High-power Electronics 822