Components of Prad and Zeff derived from X-ray spectroscopy of the main impurities in JET

We describe techniques to derive Prad components, and impurity concentrations from soft x-ray spectroscopic data. This has particular importance for the JET preliminary tritium experiment (PTE), when the close-coupled VUV and XUV grating spectrometers were inoperable due to high background radiation. A new diagnostic at JET, the Bragg rotor spectrometer, gives near-complete coverage of the soft x-ray spectrum between about 0.1 nm and 10 nm. This region contains K-, L-, or M-shell line radiation from highly ionised plasma impurities for which Z ≥ 4 (Be), and offers the potential to measure all impurity concentrations, and to derive Zeff either from the sum of the components derived from line emission or directly from the continuous level. The extension to longer wavelengths is particularly useful at JET, where radiated power and Zeff are usually dominated by light impurities such as Be and C, whose H- and He-like transitions lie between about 2.5 nm and 10 nm. Advantages of the soft x-ray region are that the spectrum is relatively uncrowded, and that all likely impurities have strong transitions for which the atomic physics is relatively well known. However, a major problem is the interpretation of central-chord line intensities in terms of local impurity concentrations, particularly for the low-Z ions. (author) 7 refs., 3 figs