Undulator Gravitational Deflection

This note estimates distortions imposed by gravity on LCLS undulator strong-backs. Because of the strongback's asymmetric cross section, gravitational forces cause both torsion as well as simple bending. The superposition of these two effects yields a 4.4 {micro}m maximum deflection and a 0.16 milli radian rotation of the undulator axis. The choice of titanium is compared to aluminum.