The joint astrophysical plasmadynamic experiment extreme ultraviolet spectrometer: resolving power

The Joint astrophysical Plasmadynamic EXperiment (J-PEX) is a high-resolution extreme ultraviolet (EUV) spectrometer (220-245 angstrom) used for the study of white dwarf atmospheres. Significant improvements have been achieved in both the normal-incidence gratings and the focal-plane detector since its first successful sounding rocket flight in 2001. The spherical laminar gratings have been replaced by paraboloidal gratings. The substrates of the new gratings have measured slope errors less than 0.35 arcsec. The gratings were recorded holographically and the rulings transferred into the silica substrates by ion etching. This procedure was followed by polymer overcoat to reduce the blaze angle of the groove profile. The detector uses microchannel plates with 6 mu m pores and a cross-strip anode, providing 17.9 mu m resolution in the dispersion direction. The detector employs a KBr photocathode with a projected efficiency of 0.24 at 256 angstrom. Using ray tracing simulations, we predict the resolving power expected from the spectrometer during upcoming EUV calibrations with a He II discharge source.