Experimental Characterization of Permanent Magnets Used in Periodic Structures

In a periodic structure, the magnetic flux density profile of a hybrid undulator depends strongly on the characteristics of its permanent magnets. A simple procedure to select the best permanent magnets for periodic magnetic structures is presented here. We used a very simple apparatus for the magnetic field measurements. We tested by assembling periodic structure prototypes formed by brick-shaped permanent magnets. Index Terms--Free electron lasers, periodic structures, permanent magnets, undulators.