English: Experimental visualization of the field line on a magnetic surface in Wendelstein 7-X. The field lines making up a magnetic surface are visualized in a dilute neutral gas, in this case primarily water vapour and nitrogen (${\displaystyle p_{n}\approx 10^{-6}\,\mathrm {mbar} }$). The three bright light spots are overexposed point-like light sources used to calibrate the camera viewing geometry.