Measurements of the intercombination and forbidden lines from helium-like ions in Tokamaks and Electron Beam Ion Traps

The paper reviews the results from tokamak experiments for the line ratios x/w, y/w, and z/w from helium-like ions with Z in the range from 14 to 28. With exception of the DITE experiments, where these line ratios were found to be in agreement with theoretical predictions, all other tokamak experiments yielded values that were significantly larger than predicted. The reasons for these discrepancies are not yet understood. It is possible that radial profile effects were not properly taken into account in the majority of the tokamak experiments. The paper also gives a short historical review of the X-ray diagnostic developments and also presents very recent data from a new type of X-ray imaging crystal spectrometer, which records spatially resolved spectra with a spatial resolution of about 1 cm in the plasma. These new data can be Abel inverted, so that it will be possible to determine line ratios at each radial position in the plasma. Effects of radial profiles, which may have affected the chord-integrated measurements of the past, will thus be eliminated in the future

Dielectronic satellite spectrum of helium-like iron (Fe XXV)

Dielectronic satellite spectra of Fe XXV near 1.8500 A have been observed from PLT (Princeton Large Torus) tokamak plasma discharges for electron temperatures in the range from 1.5 to 3 keV and an electron density of 2 x 10/sup 13/ cm/sup -3/. The electron temperature was independently determined from the electron cyclotron radiation emitted by the plasma. The quality of the spectra allows a detailed comparison with theoretical prediction, which is of importance in view of diagnostic applications

Stochasticity and the m = 1 mode in tokamaks. [Sawtooth oscillations]

It has recently been proposed that stochasticity resulting from toroidal coupling could lead to a saturation of the m = 1 internal mode in tokamaks. We present results from the nonlinear evolution of the m = 1 mode with toroidal coupling that show that stochasticity is not enough to cause saturation of the m = 1 mode

X-ray analysis of nonMaxwellian distributions (current drive)

The plasma bremsstrahlung emission is utilized to determine the shape of the electron velocity distribution in situations where it deviates strongly from a Maxwellian distribution. The instrumentation used to measure the hard x-ray emission is briefly discussed. Model calculations show that polarization measurements give best results for unrelativistic tails with tail temperatures T/sub b/ 50 keV. The techniques were originally developed in order to analyze runaway discharges. Recently, they found new interest because of the formation of energetic electron tails during current drive. The first x-ray results from the current drive during LH heating on PLT are discussed

Successor oscillations of internal disruptive instabilities in the PLT tokamak

The experimentally observed persistence of the m = 1 mode following an internal disruption is described. The hot central region appears to spiral outward, being pared by interception with the radius of q = 1 (as deduced from the radial extend of the m = 1 mode). The outward motion of the axis can be arrested and the surviving helical filament can subsequently spiral inward, rather than being annihilated as expected from nonlinear resistive internal kink mode simulations

Observations of several disruptions in PLT using soft and ultra-soft x-ray radiation

The evolution of ultra-soft x-ray radiation (USX, h..nu.. approx. > 100 eV) is compared to that of the soft x-ray radiation (SX, h..nu.. approx. > 1000 eV) during several disruptions in PLT. Spatial resolution is obtained in both cases by arrays of silicon surface barrier detectors viewing along different chords. During some disruptions the USX behaves quite differently from the SX, and a classification is made based on the USX behavior. Different interpretations of the data are discussed, along with the possibility that these measurements may distinguish between the roles of temperature and impurity density changes during disruptions