If the electrons were to travel through air as they orbited the Diamond storage ring they would very quickly collide with air molecules and be lost from the electron beam.
To minimise these losses, the electrons circulate around the storage ring in an evacuated vacuum chamber in which the pressure has been reduced to be approximately one million million times lower than atmospheric pressure. At this pressure, the lifetime of the electron beam (defined as the length of time it takes for the beam current to decay to 37% (1 divided by e) of its initial value) at Diamond will be approximately twenty hours. In simple terms, an electron could travel in that time, from the Earth to the Sun and back over 75 times!
The storage ring is constructed on a series of girders, with five to each arc. A complete achromat consists of three girders with three vacuum sections, pre-baked and installed under vacuum. There was no in-situ bake out. From arc to arc, vacuum vessels and equipment installed on each corresponding girder are identical. It is intended that for all but minor maintenance work on the vacuum vessels during the operational life of the machine, complete girders will be removed from the ring tunnel to a maintenance area and a ‘stand-by’ preconditioned girder assembly will be installed as a replacement.