Wigglers

A wigglers is a device used in particle accelerators and light sources to produce synchrotron radiation by forcing a relativistic electron beam to undergo a periodic transverse motion. It consists of a sequence of magnets with alternating polarity arranged to create a standing periodic magnetic field along the beam path.

The magnetic structure is characterized by its period, lambda_w, and peak field, B0. The electron beam follows a sinusoidal trajectory with a deflection parameter K = e B0 lambda_w /(2 pi m_e c). When K is greater than about 1, the device is described as a wiggler; for K around 1 or smaller, the device is closer to an undulator. Wigglers generate radiation with a broad spectrum and high total flux, while maintaining relatively modest spectral coherence compared to undulators.

Radiation from wigglers is emitted at harmonics of a nominal fundamental wavelength and extends over a wide energy range. The spectrum is broad and intense, making wigglers well suited for experiments requiring high photon flux, especially at hard X-ray wavelengths. However, the emission is less spectrally sharp and less coherent than that from undulators of similar electron energy.

Applications include generating bright X-ray beams in synchrotron light sources and supplying high-flux radiation for free-electron laser seeding and other experiments. Wigglers are typically installed in straight sections of storage rings and can be chosen or tuned by adjusting magnet strength, period, or electron energy.

See also: undulator, synchrotron radiation, free-electron laser.