At present the SASE3 undulator beamline of the European XFEL includes 21 planar undulators which generate
horizontally polarized radiation in the soft X-ray region between 0.4 and 5.0nm. In order to satisfy the demand to full
polarization control it is planned to install four helical undulator segments at the end of the planar SASE3 undulator
system. The helical undulator segments will be used as an afterburner, i.e. they will use the micro-bunched electron beam
and produce enhanced coherent radiation at a power level comparable to the linear system but with full polarization
control. In this contribution the properties of the emitted radiation will be investigated.
At present the SASE3 undulator line at the European XFEL is using a planar undulator producing linear polarized soft Xray radiation only. In order to satisfy the demand for circular polarized radiation a helical undulator system, the so-called afterburner is in construction. It will be operated as a radiator using the pre-bunched beam of the SASE3 undulator system. Among several options for the magnetic structure the Apple-X geometry was chosen. This is a pure permanent magnet undulator using NdFeB material. Four magnet arrays are arranged symmetrically the beam axis. Polarization can be changed by adjusting the phase shift (PS) between the two orthogonal structures. The field strength can be adjusted either by gap adjustment or alternatively by the amplitude shift (AS) scheme. For an engineering design the maximum values of forces and torques on each of the components under worst case operational conditions are important. The superposition principle is used to reduce calculation time. It is found that the maximum forces Fx, Fy and Fz for a 2m long Apple-X undulator are 1.8*10<sup>4</sup>N, 2.4*10<sup>4</sup>N and 2.3*10<sup>4</sup>N, respectively. More results are presented in this paper.