The gas system, connected with the hydraulic system, has the purpose of introducing any gas into the waterfall target container. If the experiment requires a reduction of the background the hydrogen can be used. It is made of a load and discharge tube circuit to allow the removal of the air by flushing the hydrogen into the target cell (and the water reservoir). Once the system is full the circuit is closed by electro-valves. (see the detailed description in the Appendix B)