An arrangement for manufacturing a reflector for a PTC from a rectangular reflective structure. The arrangement comprises a tensioning device configured to tension a reflector portion of the rectangular reflective structure, such that a surface of the tensioned reflector portion acquires a curvature perpendicular to the tensioned reflector portion's longitudinal propagation, along the tensioned reflector portion's longitudinal propagation. The arrangement further comprises a fixating device configured to fixate the surface's curvature, such that the tensioned reflector portion remains tensioned. The tensioning device is configured to tension the reflector portion of the rectangular reflective structure by pre-forming the reflector portion to a pre-curvature, and adjusting the pre-curvature by applying a torque at a longitudinal borderline of the pre-formed portion. Because the reflector will be maintained tensioned by torques only, it will adapt a curvature of a high precision parabola.