Coordinated Measurements of Plasma Density and Cooperative Light Scattering in a Theta‐Pinch Plasma

Measurements have been made on the spectral broadening of ruby laser light scattered at a small forward angle by density fluctuations in a theta‐pinch plasma, in order to systematically investigate the variations in scattering cross section with reverse bias magnetic field and with time during the first half‐cycle of the compression field. Measurements of density under the same plasma conditions were made so that the effects of cross section variations could be separated from density variations. The principal results are: (1) The observed cross section is approximately six times the theoretical cross section for a plasma with the Scylla III temperature and density (no bias magnetic field). The large cross section is attributed to superthermal density fluctuations (turbulence) in the plasma. (2) The scattering cross section for a plasma with a bias field of ‐800 G is three times larger than for the plasma with no bias field. (3) There is little difference in the scattering cross sections measured at two times during the discharge. (4) The density measurements show a plasma loss rate which increases with increased reverse bias field. (5) There is a strong dependence of scattering on plasma temperature; the hotter the plasma, the smaller the scattering cross section and the broader the spectral width of the scattered light.