Investigations of impurity accumulation phenomena in ASDEX are reviewed. There are four different operating regimes where pronounced accumulation is observed and these regimes are also characterized by improved energy confinement. In particular, medium-Z metallic ions are involved in accumulation processes whereas low-Z ions appear almost unaffected.

Atomic processes of interest to the magnetic fusion research are outlined. The interplay of atomic physics and plasma physics pertaining to tokamak plasmas is described. In general, the coronal approximation plus diffusive transport are necessary to account for the spectroscopic measurements. The atomic data base used in fusion research is also summarized.

Ultrasoft x-ray diode (USXRD) arrays have been used on DIII-D and ASDEX to study plasma edge radiation, in the photon energy range from 10 eV to 10 keV. The detectors are extremely useful and versatile due to their simplicity and compactness. Furthermore, absolute quantum efficiencies (QE) of many photocathodes such as vitreous C, Al, Cu, CuI, CsI, and Au have been measured in recent years. With filter technique, broadband resolution, E/ΔE∼1, is possible. Quantum-efficiency comparison of USXRD with semiconductor XRD is also presented to better understand the regions of applicability for each detector.

Toroidal rotation of the central plasma core has been observed prior to and during electron cyclotron heating (ECH) in the Doublet III tokamak [in Plasma Physics and Controlled Nuclear Fusion Research 1984, Proceedings of the Tenth International Conference, London (IAEA, Vienna, 1985), Vol. 1, p. 131]. Measurements were made using a curved-crystal Bragg x-ray spectrometer with spectral resolution of λ/Δλ of greater than 19 000 and temporal resolution of 20 msec. Ion rotation velocity was determined from the Doppler shift of x rays emitted from the plasma impurity Ti XXI resonance line. Ion temperatures were determined from the Doppler broadening of this line. A study of purely Ohmic discharges suggests that nonrotating discharges exhibit magnetohydrodynamic activity other than sawtooth oscillations, while those that rotate exhibit sawteeth. Discharges with plasma rotation prior to the appliction of ECH appear to heat more effectively than those that do not. Velocity and temperature histories show that there are temporal characteristics corresponding to whether the plasma was or was not effectively heated.