“European XFEL, a large international research facility with eleven European member countries, has begun the commissioning of the 3.4-km long underground X-ray laser. …. The commissioning will take place over the following next few months. External scientists will be able to perform experiments at the facility for the first time in summer 2017.”

See: http://www.xfel.eu/news/2016/european_xfel_starts_commissioning_of_the_worlds_largest_x_ray_laser/