Harmonic intensity suppression in an adjustable phase undulator

We consider some features of the electromagnetic radiation excitation in an adjustable phase undulator. This device consists of two rows of the permanent magnet blocks, one above and the other below a flat section of the electron vacuum chamber. One row of permanent magnet blocks can slide to the other at a constant gap in the longitudinal direction. We show that the shape and intensity of each harmonic may be efficiently changed (suppressed). This property can be used in free electron lasers and undulator radiation experiments.