Magnetic measurements on the undulator prototype for the VUV-FEL at the TESLA Test Facility

For the VUV-FEL at the TESLA Test Facility a 30 m long combined function undulator is under construction which integrates an alternating sequence of focusing and defocusing quadrupoles (FODO lattice) with an sinusoidally varying undulator field having a period length of 27.3 mm. First results of magnetic measurements were performed on a 0.9 m long prototype structure and are reported and discussed in this contribution. The peak field, the gradient of the superimposed quadrupolar field as well as the adjustability of the quadrupole strength and the exact location of its axis in horizontal and vertical direction were measured. The results demonstrate that the proposed combined function magnet structure is very promising for the use in the SASE FEL at the TESLA Test Facility.