The new APPLE X undulators are novel elliptically-polarised undulators, which have a highly symmetric geometry. Theoretically, all the elliptical polarisation states are expected to have the same deflection parameter if the magnetic and geometrical errors are negligible. Nonetheless, the magnetic measurements of the first ten APPLE X undulators performed at Paul Scherrer Institut (PSI) contradicted this simple statement and numerical simulations were required to understand and validate the results. After the valuation of the magnetic-force induced mechanical deformations of the undulator frame, the central role played by the magnetic susceptibility $\chi$ was investigated. The simulation results indicate that the impact of different magnet types in the Halbach array, the anisotropic properties, and the choice of shaped field radial magnets are critical for the achieved magnetic field. The numerical results are compared with the measurement data.

新型APPLE X波荡器是新颖的椭圆极化波荡器，具有高度对称的几何形状。从理论上讲，如果磁和几何误差可忽略不计，则所有椭圆偏振态都应具有相同的偏转参数。尽管如此，Paul Scherrer Institut（PSI）对前十个APPLE X起伏器进行的磁测量结果与这一简单陈述相矛盾，因此需要进行数值模拟才能理解和验证结果。在对起伏器框架的磁力诱导的机械变形进行评估后，磁化率起着核心作用$\chi$被调查了。仿真结果表明，Halbach阵列中不同磁体类型的影响，各向异性特性以及成形磁场径向磁体的选择对于实现磁场至关重要。将数值结果与测量数据进行比较。