Application of the penning discharge for cleaning mirrors in optical diagnostics of the ITER

The possibility of using the reflective gas discharge at a direct current (DC) in a strong uniform magnetic field for cleaning mirrors in optical diagnostics of the ITER is studied. A mirror and an additional Penning-type electrode, which was shifted along the magnetic field, were used as sputtered cathodes forming the discharge cell. The experiments were performed in gaseous He, in a magnetic field of up to 0.5 T at a discharge voltage of up to 750 V. Mo, Al and Mo mirrors with an Al coating, simulating a Be impurity, were used as materials of the cathodes. It is shown that this system efficiently cleans Mo mirrors from Al films with a thickness of up to 200 nm, recovering the initial optical properties of the mirror. Integration versions of cleaning systems of this type into the first-mirror assembly for the ITER are proposed for the example of Hα diagnostics.