The millimeter-wave system of the remote steering launcher at the upper port level is composed of beamlines that are rated for 2-MW continuous-wave operation at 170 GHz. In each beamline, a torus window is located between the entrance to the in-vessel square corrugated waveguide and the steerable mirrors in the launcher back end. In the reference design, the maximum steering angle of 12 deg imposes a 27-mm off-center beam shift to the window disk center, which in turn leads to asymmetrical heating of the window. This raises particular concerns of enhanced thermomechanical stresses in the window and in the metallic window cuffs. In order to qualify the optical, mechanical, and thermohydraulic design, high-power short-pulse and thermohydraulic tests were performed using a prototype chemical vapor deposition diamond torus window developed and manufactured at Forschungszentrum Karlsruhe. It was proven that arcing did not occur even under maximum millimeter-wave power levels available (up to 0.53 MW) and that the millimeter-wave beam profile was fully maintained. A test facility allowed thermohydraulic studies of the window cooling system with parameters characteristic for component cooling water loops at ITER (pw = 1.0 MPa, Tw = 40°C).