Line classifications for Ni XXV and XXVI and new observations of Fe XXIII and XXIV in laser-produced spectra

Spectral line classifications and wavelength measurements are presented which provide essential data for the interpretation of soft X-ray spectroscopic observations of solar flares. Ni XXV and Ni XXVI spectral lines are identified in spectra emitted from plasmas formed by focusing the output of the Rutherford Laboratory multigigawatt neodymium laser on to plane solid targets at an irradiance of about 1016 W cm2. A photographic beryl crystal spectrograph was used to record spectra in the wavelength range 8–13 Å. Line classifications were made with the aid of theoretical calculations of wavelengths and oscillator strengths. New observations of isoelectronic Be I-like Fe XXIII and Li I-like Fe XXIV spectra are also presented. The relevance of the data to the interpretation of solar flare spectra is discussed.