Z eff spatial profiles from Bremsstrahlung emission in the near infrared spectral region

Measurements of plasma radiation in the infrared (IR) BREM_IR range (λ=978 nm , Δλ=38 nm ), at 16 horizontal lines of sight intersecting the central vertical chord of the [Frascati Tokamak Upgrade (FTU) R=0.935 m , a=0.3 m , B=4–8 T ], from z=−0.22 m below, to z=0.08 m above the equatorial plane, are performed using the detection system of the Thomson scattering apparatus [F. Orsitto et al., Appl. Opt. 34, 2712 (1995)] (TS). The measured BREM_IR intensity is equal I(z)=〈Z eff Gn e 2 /T e 1/2 〉 where 〈〉 means line average. For determining the Z eff , the Gaunt factor (G) is needed, and the Born–Elwert formula is used. The Z eff spatial profiles are determined using the plasma temperature (T e ) and density (n e ) measured by the TS, DCN interferometer, and Abel inverted intensity profiles. Z eff (r) versus time behavior in FTU discharges is presented for krypton injection experiments aimed to investigate the particle confinement behavior during strong injection of impurities.