Characterization of the JT-60U divertor plasma region during the formation of a strong radiation

High resolution spectra emitted by C3+ ions and measured along vertical chords in the divertor of the JT-60U tokamak in presence of an X-point MARFE are compared to synthetic profiles calculated taking into account Doppler and Stark effects but not the Zeeman effect because the latter was suppressed experimentally thanks to a linear polarizer transmitting only the component parallel to the toroidal magnetic field. For each viewing chord, the electron density is obtained using equal ion and electron temperatures determined from C IV line intensities observed with a large band visible spectrometer. In complement to the electron temperature distribution obtained previously from line intensities and collisional-radiative modeling, a spatial distribution of the electron density is obtained here for the JT-60U detached divertor with an X-point MARFE. For spectra measured along the most central viewing chords with respect to the MARFE (intensity peak of the strong radiation), it is suggested from the spectral fitting that the emission comes from two plasma layers whose parameters have been obtained (copyright 2012 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)