Heat can be pumped into the anode much faster than it can be lost by radiation, and so one way in which the power handling capacity of a tube can be increased, at least for short exposure times is to increase the mass of the anode. If a large disk of tungsten is used, the weight of the anode places a huge amount of stress on the bearings, leading to premature failure.
The anode of the tube shown here is a composite anode. A ring of tungsten is mounted in a block of carbon, which has a high thermal capacity combined with low weight. A tube of this type would be used for Angiography or perhaps CT.

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