Extensive studies of the H-mode density limit (DL) in JET gas-puffed discharges have been performed in the past four years targeting at an improved database for extrapolation to ITER. This paper reviews the arguments for the particular DL definition (pedestal density at the H-L boundary), the logic underlying the choice of parameters under focus (toroidal field, major radius, triangularity, safety factor) as well as some improvement in the interpretation of typical JET density ramp-up signatures that led to a critical review of the existing data. An empirical scaling is derived and compared with existing empirical and model based scalings. ASDEX Upgrade data are included in this analysis to provide information on the size dependence. The main results are: earlier findings on the B t , R and q 95-dependences are confirmed. The triangularity dependence, if any, is weak. The SOL-based BLS (Borrass, Lingertat, Schneider) scaling and the empirical scaling are virtually indistinguishable. The Greenwald scaling provides values in the right absolute range, but the overall fit is comparatively poor. The proposed scaling predicts ITER critical densities considerably below the reference value. Fuelling methods other than gas-puffing are outside the scope of this paper, but pellet fuelling, envisaged for ITER as an option to alleviate the situation, is discussed.
Resonance lines of nickel-like highly-charged ions are identified in the spectra of seven elements (Ta, W, Re, Pt, Au, Hg and Pb) excited by laser irradiation.They pertain mainly to transitions 3d-nf (n = 5 through 9), 3 p n d (n = 4 through o) and 3s-np (n = 4, 5). Unresolved transition arrays of lower charge ions isoelectronic with copper, zinc, gallium and germanium, are also interpreted, as well as a few cobalt-like transitions. The relativistic parametric potential method and the unresolved transition array formalism support this analysis.
Multicharged ions of strontium have been produced by laser irradiation (0.53 μm) of strontium targets with laser intensities of about 1014 W/cm2 on the target. Their spectrum has been observed with a crystal spectrograph in the range 4.5-7 Å and with a grazing-incidence spectrograph from 115 to 208 Å. Eight prominent lines previously identified as Sr XXVII and Sr XXVIII were used as internal standards for deriving wavelengths of about ninety lines from 115 to 208 Å. Ab initio evaluations of energies and transition probabilities in Sr XXVII by the relativistic parametric potential method support the identification of the configurations 3s3p, 3p3d, 3s3d and 3p2 which are now almost complete. Some weaker lines are attributed to Al-like Sr XXVI and Ne-like Sr XXIX.
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