HELIUM-LIKE SULFUR X-RAY-EMISSION IN SOLAR-FLARES AND LABORATORY PLASMAS

Theoretical X-ray spectra of He-like sulphur (S XV) derived from the G eneral Relativistic Atomic Structure Package, the Dirac R-matrix code and other calculations are compared to laboratory spectra obtained fro m the Alcator C tokamak and JET, and solar flare spectra obtained from the Yohkoh Bragg Crystal Spectrometer (BCS) and with the SMM Flat Cry stal Spectrometer. The spectra depend on electron temperature and elec tron density for plasma densities greater than 10(14) cm(-3). The fits of the derived synthetic spectra to the laboratory spectra at measure d density and temperature are in fair agreement. Very good agreement c an be achieved with the solar flare spectra, which are in general cons istent with the S XV low-density limit, by adjusting temperature. Thus , S XV line spectra can be used to determine the temperatures of relat ively weak flares for which diagnostics from higher-temperature ions a re unavailable. Using the synthetic spectra, a search for density effe cts in Yohkoh BCS data at the time of compact flares was made. None wa s found, so that it can be deduced that for such flares the electron d ensity is less than 10(14) cm(-3). Density estimates are made from emi ssion measures and image sizes using Yohkoh Soft X-ray Telescope data. Research has been carried out with the results of laboratory spectra which indicate a variation of the I(x)lI(y) line intensity ratio acros s the tokamak minor radius. We have studied various flares which occur at different locations across the solar disk to determine if the same effect exists on the Sun.