Magnetic design optimization of the undulator for the VUV-FEL at the TESLA Test Facility

For the VUV-FEL at the TESLA test facility an undulator with superimposed strong focusing will be needed. A period length of 27.3 nm, a peak field of 0.5 T at a gap of 12 mm and a quadrupole gradient of about 20 T/m are required. In this report a magnetic design is presented which allows for these properties. Because it is a planar structure, it allows also for free access from the side for magnetic measurements and insertion of a vacuum chamber. In numerical calculations using the 3D code MAFIA the parameters for the magnet structure were optimized. Criteria for the selection of magnetic material are established. Forces acting on the magnetic components were calculated