Time-resolved x-ray energy spectrometry as a plasma diagnostic method for the Oak Rige tokamaks

A discussion of the x-ray emission spectrum from a tokamak plasma is presented, and the complicating effects of plasma-detector geometry, plasma temperature and density profiles, and impurity radiation are analyzed. The necessary data collection system is described, and the consequences of finite energy resolution, pulse pileup, and other deleterious effects are investigated. Results of these considerations are combined in a procedure to calculate T_e and Z_eff from x-ray energy data and plasma density information, and to estimate the accuracy and reliability of the derived values.

The computational procedure is applied to five different classes of tokamak discharges and the results are compared with T_e. and Z_eff values independently derived through a Thomson-scattering diagnostic. These comparisons show that, in general, agreement between the x-ray diagnostic and accepted techniques is good, and demonstrate the advantages of a time-resolved measurement capable of spanning an entire discharge. Where discrepancies op exist between x-ray and Thomson-scattering results, there is other evidence that the basic physics of those particular c discharges is not understood. It is concluded that the x-ray technique provides useful and unique on-line diagnostic, yielding T_e and Z_eff determinations good agreement with other measurements for well-behaved plasmas, and providing additional information to aid in t understanding anomalous ones.