VACUUM ULTRAVIOLET RADIATION FROM PLASMAS

Abstract

A study of the generation and transfer of radiation in gases at temperatures greater than 10 000° K usually involves spectroscopy in the vacuum ultraviolet spectral region, whether for the determination of such quantities as oscillator strengths, line shapes, and absorption coefficients fundamental to an understanding of the detailed emission and absorption processes transpiring in the medium, or for the laboratory simulation and identification of spectral lines such as observed by astrophysicists. Results of such endeavors are equally important to an understanding of the plasma physics and of mechanisms of energy loss which often determine the maximum heating rate of, for example, controlled fusion devices, as well as to astrophysicists in the formulation of model atmospheres and the determination of stellar structure. For these purposes, laboratory sources are needed which operate at high enough density to produce useful spectra and yet are capable of simulating temperatures and equilibrium conditions of interest to astrophysicists. To this end a T-type electromagnetic shock tube operating at ∼20000°K has been developed to generate a uniform high density atmosphere into which tracer gases are added in controlled amounts, producing variable degrees of opacity in the vicinity of broadened spectral lines of known shape, such as the Lyman series of hydrogen. Also, two θ-pinch devices operating at temperatures in the million-degree range, suitable for simulating corona equilibrium conditions and solar spectra as well as producing resonance lines of variable optical depth, are described. Experimental complexities peculiar to various regions of the extreme ultraviolet from 10 å to 2000 å are outlined, as is a discussion of absolute intensity determinations.