Passive spectroscopic diagnostics for magnetically confined fusion plasmas

Spectroscopy of radiation emitted by impurities and hydrogen isotopes plays an important role in the study of magnetically confined fusion plasmas, both in determining the effects of impurities on plasma behavior and in measurements of plasma parameters such as electron and ion temperatures and densities, particle transport, and particle influx rates. Spectroscopic diagnostics of plasma radiation that are excited by collisional processes in the plasma, which are termed passive spectroscopic diagnostics to distinguish them from active spectroscopic diagnostics involving injected particle and laser beams, are reviewed. A brief overview of the ionization balance in hot plasmas and the relevant line and continuum radiation excitation mechanisms is given. Instrumentation in the soft X-ray, vacuum ultraviolet, ultraviolet, visible, and near-infrared regions of the spectrum is described and examples of measurements are given. Paths for further development of these measurements and issues for their implementation in a burning plasma environment are discussed.