Abstract: The disclosure relates to very high power (one megawatt and more) electron tubes with cylindrical anodes. To cool the anode, which receives about one kilowatt per square centimeter, water is usually made to circulate in a jacket surrounding the anode with grooves to facilitate ebullition. The invention proposes a structure where the anode wall is drilled in its thickness and throughout its height with very fine and very numerous water circulation conduits. The anode is made in many superimposed sections brazed to one another by their edges. The conduits are formed in the individual sections before this brazing operation. The channels all lead into a structure for the distribution of cooling water which distributes the water uniformly in all the tubes. The anode can thus distribute a flux with power of over 2 kW/cm.sup.2 on a surface area of over 1000 cm.sup.2.