X-RAY SPECTROSCOPIC DIAGNOSTICS OF CORE ION CONFINEMENT IN LARGE (JET) AND MEDIUM-SIZE (COMPASS) TOKAMAKS

Sophisticated X-ray spectroscopic instruments have been developed and used for confinement studies in tokamaks at JET and Culham Laboratory. The Bragg rotor survey spectrometer, when programmed to operate in mo nochromatic or limited spectral range (LSR) modes, has been used to de rive transport coefficients from the transient spectral signature of i njected, non-recycling, test ions. The coefficients appropriate to spe cific confinement regimes have been investigated with respect to ion c harge state and tokamak machine parameters. The LSR mode allows discri mination against background X-ray light, a particularly serious proble m at high electron density, n(e) approximate to 10(20) m(-3), in H mod e where there is evidence, in COMPASS-D, for modest accumulation of im purities. Impurity ion accumulation is observed most clearly in passiv e spectroscopic studies of the 1s(2)-1s2p line emission from intrinsic impurity ions such as Cl(XVI) using a high resolution Johann configur ation crystal spectrometer. Line shapes and line ratios within the lim ited spectral range 4.45-4.50 Angstrom are interpreted in terms of ion and electron temperature and ion fluid velocity. In particular, the ' q'/'w' line intensity ratios are interpreted in terms of the relative abundance of the Cl(XV)/Cl(XVI) ions which are modelled in terms of io n transport. These continuous, passive measurements of ion confinement are compared with results from the transient injection method. Absolu te levels of the X-ray continuum, adjacent to the Cl(XVI) lines, are u sed to derive Z(eff). Both the Bragg and Johann X-ray spectrometers ha ve been calibrated for absolute photon sensitivity. The efficiencies o f the diffractors in these instruments can be measured using a newly d eveloped, two-axis goniometer. (C) 1997 Elsevier Science S.A.