Insertion device
They are periodic magnetic structures that stimulate highly brilliant, forward-directed synchrotron radiation emission by forcing a stored charged particle beam to perform wiggles, or undulations, as they pass through the device.
However it was Motz and his team who in 1953 installed the first undulator in a linac at Stanford, using it to generate millimetre wave radiation through to visible light.
[1] It was not until the 1970s that undulators were installed in electron storage rings to produce synchrotron radiation.
Undulators only became practical devices for insertion in synchrotron light sources in 1981, when teams at the Lawrence Berkeley National Laboratory (LBNL), Stanford Synchrotron Radiation Laboratory (SSRL), and at Budker Institute of Nuclear Physics (BINP) in Russia developed permanent magnetic arrays, known as Halbach arrays, which allowed short repeating periods unachievable with either electromagnetic coils or superconducting coils.
Despite their similar function, wigglers were used in storage rings for over a decade before they were used to generate synchrotron radiation for beamlines.
Wigglers have a damping effect on storage rings, which is the function to which they first put at the Cambridge Electron Accelerator in Massachusetts in 1966.
Since these first insertions the number of undulators and wigglers in synchrotron radiation facilities throughout the world have proliferated and they are one of the driving technologies behind the next generation of light sources, free electron lasers.
As the stored particle beam, usually electrons, pass through the ID the alternating magnetic field experienced by the particles causes their trajectory to undergo a transverse oscillation.
There is very little mechanical difference between wigglers and undulators and the criterion normally used to distinguish between them is the K-Factor.
The K-Factor determines the energy of radiation produced, and in situations where a range of energy is required the K-number can be modified by varying the strength of the magnetic field of the device.
In a wiggler the period and the strength of the magnetic field is not tuned to the frequency of radiation produced by the electrons.
In an undulator source the radiation produced by the oscillating electrons interferes constructively with the motion of other electrons, causing the radiation spectrum to have a relatively narrow bandwidth.
of the radiation emitted by an insertion device can be calculated using the undulator equation: where
