Fig. 7: Upper divertor gas valve system identification in Super-X divertor configuration.

a, Poloidal cross-section showing the EFIT++ magnetic equilibrium reconstruction (t = 0.55 s) with a conceptual illustration of the upper divertor Dalpha filterscope sightline, upper divertor valve location and lower divertor Fulcher band front position Ltar. b, Time domain (top) and frequency domain (bottom) response of the detrended lower divertor Fulcher band front position Ltar around the operating point. c, MWI Fulcher band inversion (t = 0.55 s), indicating highly detached conditions. d, Time domain (top) and frequency domain (bottom) response of the detrended upper divertor Dalpha filterscope (-) around the operating point to a perturbation of the requested upper D2 divertor gas valve flow rate (--). All data from experiment number 49298.