Undulator tunability and ring-energy

An Undulator has two properties which make it an extremely attractive source of electromagnetic radiation. The first is that the radiation is concentrated in a number of narrow energy bands known as harmonics of the device. The second characteristic is that under favorable operating conditions, the energy of these harmonics can be shifted or {open_quotes}tuned{close_quotes} over an energy interval which can be as large as two or three times the value of the lowest energy harmonic. Both the photon energy of an undulator as well as its tunability are determined by the period, {lambda}, of the device, the magnetic gap, G (which is larger than the minimum aperture required for injection and operation of the storage ring), and the storage ring energy, E{sub R}. Given the photon energy, E{sub p}, the above parameters ultimately define the limits of operation or tunability of the undulator