Pfingstner, J. Adli, E. TUP011 undulator simulation electron FEL operation 2015 2015-12 The X-band FEL collaboration is currently designing an X-ray free-electron laser based on X-band acceleration technology. This paper reports on the recent progress on the design of the undulator part of this machine including simulations of the X-ray production process. The basic parameters have been chosen and a beam transport system has been designed, considering strong and weak focusing of quadrupole and undulator magnets. Simulations of the X-ray production process have been carried out with realistic input beam distributions from particle tracking studies of the linac design team. The expectable X-ray properties for SASE and seeded FEL operation have been investigated and also undulator taper options have been studied.