An overview of accelerator types. For low accelerating voltage, e.g., for TV's or X-ray tubes, the electrostatic accelerator is the most economic. In the linear accelerator a lot of rf-cavities are put after each other such that an electron may be accelerated successively in each cavity. Linear accelerators have the advantage that they can accelerate a lot of current to very high energy (voltage). At high energy they become very costly, though. Linear accelerators are used for cancer-therapy. Alternative to the linear accelerator one may also bend the electron back to the entrance of the accelerator. The circular design shown is known as a synchrotron. BESSY employs such an accelerator scheme to accelerate the electrons.