The influence of a constant magnetic field on the radiation of a planar undulator is studied analytically with the use of generalized Bessel functions. The behavior of on-axis radiation intensity in the undulator and the influence of a magnetic field on off-axis radiation are investigated. The critical magnitude of the constant component of the magnetic field, which has a significant effect on the motion of electrons in the undulator, is calculated analytically. The examples of several planar undulators are discussed, and the influence of the Earth’s magnetic field on their spectrum is evaluated.
41.60.Ap Synchrotron radiation
41.60.Cr Free-electron lasers
52.59.Rz Free-electron devices
$^1$ENEA Research Center, Fis-Mat, 00044, Frascati, Rome, Italy
$^2$Faculty of Physics, Moscow State University, Moscow, 119991, Russia
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