Accelerator cavities, from the CEBAF accelerator at Jefferson Lab (upper) and the International Linear Collider (ILC) (lower).  Both cavities are built of niobium and are designed to operate at a frigid 2 Kelvin. The ILC cavities have a different shape for reaching higher accelerator gradients (a cavity's ability to transfer energy into particles per unit of cavity length).  They are also longer, consisting of nine cells per cavity versus the five-cell cavities at Jefferson Lab.

[Jefferson Lab, 2006]