|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.