Variable period undulator with tunable polarization

The proposed magnetic structure allows to control all the parameters of the sinusoidal magnetic field B(s)=B₀·sin(2πs/λ_U+ϕ) of permanent magnet undulator: amplitude B₀, period length λ_U, and phase ϕ. The magnetic structure consists of diametrically magnetized cylindrical magnets at fixed positions. The field is adjusted by motorized rotation of each magnet. Tuning of radiated wavelength by changing the period length instead of field amplitude is more effective and results in a wider wavelength range and higher photon flux, especially for free electron lasers. Individual adjustment of the magnets allows for creating arbitrary shaped magnetic field and also for embedding other elements like phase shifters, dipoles, or multipole lenses into the undulator magnetic structure.