An Extreme Ultraviolet Optics-Free Spectrometer With Improved Spectral Resolution and High Signal-to-Noise Ratio

A computer model of an Extreme Ultraviolet (EUV) spectrometer based on a gas ionization chamber and on flight experience of the Optics Free Spectrometer (OFS previously flown), was built and tested with the SIMulation of IONs (SIMION) tools. Our goal in this work was to design an improved and simplified electron beam focusing system which fits the dimensions (D = 180 mm; L = 380 mm) available for installation of a new OFS instrument in our sounding rocket flights, and to lower the focusing potentials from the 5,000 V in the previous OFS computer model to about 300 V in the current model. The advanced EUV OFS employs a six-electrode electron beam focusing system with focusing potentials of up to 250 V and can focus photo-electrons in a spectral range of 5.0 – 50.0 nm. The spectral resolution may be optimized throughout the whole spectral range by switching to an appropriate set of focusing potentials resulting in a resolution of about 0.10–0.25 nm, which is comparable to or better than the spectral resolution of typical EUV grating spectrometers designed for spaceflight applications. Modeled focusing of photo-electrons at the detector’s aperture permits an increase in both spectral resolution and Signal to Noise Ratio (SNR) compared to those obtained with the dual-electrode OFS prototypes flown previously. A comparison of measured OFS EUV spectra (sounding rocket flight of 2003/12/05) with the modeled spectra showed that an advanced OFS for studying solar dynamics in the EUV with high spectral and temporal resolution is indeed quite feasible.