A spectroscopic determination of electron temperature in a high temperature plasma

The electron temperature of a high temperature plasma is determined by measuring the intensity ratio of the 2s-2p and 2s-3p transitions in the same L1-like ion. The theoretical dependence of the intensity ratio on electron temperature is given for several Li-like ions between C IV and Si XIII. It is assumed that the free electrons have a Maxwellian distribution of velocities and that the distribution of electron populations over the bound levels is given by a coronal-type equation. A collisional excitation cross section derived by Seaton is used. The use of spectral lines emitted by the same ion and with a common lower level gives an intensity ratio that is a function of electron temperature only and is free from several ambiguities which may arise from spatial and temporal variations. The method can be used for measurements of electron temperature between about 5 ev and 200 ev. This method has been used to determine the electron temperature of the pulsed deuterium plasma in ZETA over a wide range of conditions by measuring the intensity ratio of the N v 1238.8 Å and 209.3 Å lines photoelectrically with a grazing-incidence monochromator. A relative photometric calibration was obtained, firstly from the known relative photoelectric yield of a tungsten reference cathode, and secondly by using the branching ratio method with the He II ion. The errors in the measurement of electron temperature arising from random and systematic errors in the measurement of the intensity ratio are also discussed.