Experimental Study of Atomic Processes in the Text Tokamak Plasma.

The present work examined several electron-ion collision theories by measuring spectral line intensity ratios, and applied atomic structure theories to determine spectroscopically the tokamak plasma safety factor. The TEXT tokamak provided a steady spectral source in a low -density and high-temperature plasma. The line intensity ratio measurements for transitions with Delta n = 0(2 - 2) for C sc III-Ne sc VII and Cl sc XIV-Cr sc XXI show that for the low-Z ions the R-matrix method gave accurate predictions of electron -ion collision rates while the distorted wave approximation did not, and that predictions based on the distorted wave approximation became accurate for the high-Z ions. However, the line intensity ratio measurements for the Deltan = 1 (3 - 2) transitions for O sc V-Ne sc VII showed that none of the above computation methods gave correct collision strengths for 2s ^2 - 2s3p and 2s2p - 2s3p transitions. Spectroscopic methods were also developed for the tokamak poloidal magnetic field measurement. A scanning circular polarimeter was built for the experiment, and the circular polarization of the intrinsic Ti sc XVII 3834A line emitted by a magnetic dipole transition was studied. This provided a well-reproducible, but non-local, measurement. Spectral lines of Deltan = 1 transitions between highly excited states of intrinsic hydrogenic ions, which are populated by charge-exchange and recombination processes during a neutral beam injection, may provide a localized spectral source. A computational analysis of the circular polarization of theses lines has been performed. Alternatively, a lithium beam was injected into the tokamak plasma to provide a well-localized Li sc I 6708 A emission for spatially resolved measurements. Derived from the measured magnetic field profiles, values of safety factor on the axis for the TEXT plasma during sawtooth discharges were consistently near unity, and fell far below unity during non-sawtoothing discharges associated with the electron cyclotron resonance heating.