Identification of bits under the bonnet

Evening all,

2004 TD4, r/h (as you're stood looking at it) side of the engine under the heater pipes there is a thing that looks like a bellows.

What is it?

There is a vacuum hose attached to one end of it which is under the heater hoses and they have worn this pipe somewhat. I intend to replace said pipe.

Hopefully available separately…

i think it might be called vacuum tank

Vacuum accumulator for the turbo actuator ......?

Thanks guys, just had a quick Google search which turned up this. Although for BMW, it looks like I can get the bit of pipe I want separately…