THE CORONAL DIAGNOSTIC SPECTROMETER FOR THE SOLAR AND HELIOSPHERIC OBSERVATORY - EXPERIMENT DESCRIPTION AND CALIBRATION

The Coronal Diagnostic Spectrometer (CDS) to be flown aboard the ESA/N ASA Solar and Heliospheric Observatory (SOHO) is designed to probe the solar atmosphere through the detection of spectral emission lines in the extreme ultraviolet (EUV) wavelength range 15 nm to 80 nm. By obse rving the absolute and relative radiance of selected lines and line pr ofiles, we will be able to derive temperature, density, flow and abund ance information for the plasmas in the solar atmosphere. Spatial and temporal resolutions of down to a few arcseconds and 1 second, respect ively, allow such studies to be made within the fine-scale structure o f the solar corona. Simultaneous coverage of large-wavelength bands pr ovides the capability for simultaneously observing the properties of p lasmas across the wide temperature ranges of the solar atmosphere. The pre-launch calibration is achieved through the use of a hollow cathod e discharge source which is used as a transfer standard to allow calib ration of the CDS against the primary standard of the BESSY electron s torage ring in Berlin. The transfer source provides a radiation source of calibrated radiant flux stable to a few percent. By the use of dif ferent selected gases in the discharge tube, each of the detector wave length intervals in the CDS can be covered adequately. The pre-deliver y calibration of the CDS has been performed and some results are shown .