End effects in the magnetic field of free electron lasers with sheet electron beams

Abstract

We calculate the magnetic field of a free-electron-laser's wiggler of a recent design (Granatstein et al. Appl. Phys. Lett. 74, 643 (1985)) using sheet electron beams. We did not assume periodic boundary conditions, as was done in their work, and we obtained analytical expressions in two of the three space variables. We found various irregularities in the field behavior that were dependent on the size of the wiggler in the x direction (parallel to the beam's wide size), and that increased up to a width an order of magnitude greater than the height of the beam channel. These irregularities had been observed in field measurements. A method consisting of making the end magnets thinner worked effectively to reduce the irregularities. We also studied a similar magnetic configuration with free and independent currents and no magnets, and added the additional degree of freedom of programming the currents to further reduce the irregularities.