Spectrometer Throughput Dr Peter Young Consortium meeting, 3 March 2006

Dr Peter YoungSolar Orbiter, EUS Consortium Meeting, Mar 06 Overview Assume NI design Considerations –optical surface coatings –groove efficiency –detector quantum efficiency –filters Other things –spatial inhomogeneities –dynamic range

Dr Peter YoungSolar Orbiter, EUS Consortium Meeting, Mar 06 Coatings Multilayer coating –reflectivity taken from plot of Barry Kent SiC coating –reflectivity obtained from Fig. 23 of EUS trade-off document Remember: coating counted twice (mirror & grating)

Dr Peter YoungSolar Orbiter, EUS Consortium Meeting, Mar 06 Groove efficiency Assumed value of 80 % (R. Thomas, previous consortium meeting)

Dr Peter YoungSolar Orbiter, EUS Consortium Meeting, Mar 06 Detector UV-sensitive, back-thinned APS detector –only below 800 Å –QE plot from Nick Waltham Standard APS detector mated to a micro-channel plate (MCP) –KBr coating for MCP –MCP QE from SUMER

Dr Peter YoungSolar Orbiter, EUS Consortium Meeting, Mar 06 Aluminium filter Required to make APS detector visible blind (in absence of MCP) Single filter, placed on detector Transmission obtained from Fig of Lang et al. (2002) for Solar-B/EIS –150nm of Al, with 15nm oxide layer Transmission numbers: –around 50% at 200 Å –around 20% at 600 Å –zero above 800 Å

Dr Peter YoungSolar Orbiter, EUS Consortium Meeting, Mar 06 Design Options The following options are considered No. 4 is a hybrid design for covering all wavelength bands DesignCoatingFilterDetector 1MLYesUV-APS 2SiCYesUV-APS 3SiCNoMCP-APS 4MLYes/NoMixed

Dr Peter YoungSolar Orbiter, EUS Consortium Meeting, Mar 06 Results Efficiencies expressed as % of photons that make it to detector Assumes 171 is at peak of multilayer Wavelength/ÅDesign 1Design 2Design 3Design % %0.74 %2.61 %0.13 % %0.22 %

Dr Peter YoungSolar Orbiter, EUS Consortium Meeting, Mar 06 Count rates Photons per second for average quiet Sun: LineQS intensity (erg/cm 2 /s/sr) Design 1Design 2Design 3Design 4CDS (measured) Fe IX Fe XII Mg X O V C III O VI

Dr Peter YoungSolar Orbiter, EUS Consortium Meeting, Mar 06 Summary If 100 counts in a line is considered the minimum for performing EUS science (intensity, centroid) … then for strong lines this can be achieved in ≤ 5 seconds for all lines except Mg X λ624.9 This is a big improvement over CDS, SUMER and EIS

Dr Peter YoungSolar Orbiter, EUS Consortium Meeting, Mar 06 Other considerations A feature that is spatially resolved at 1 AU will yield the same count rate when observed at 0.25 AU A feature not spatially resolved at 1 AU will have a count rate up to 16 times larger at 0.25 AU

Dr Peter YoungSolar Orbiter, EUS Consortium Meeting, Mar 06 Detector dynamic range CDS: variation in intensity along slit for quiet Sun is typically a factor 20 In active regions this can rise to a factor 200 Moving to 0.25 AU, expect these factors to increase by factor 16 Improving on the CDS spatial resolution (8”  1”) gives another factor of 8 Intensity contrast could be as much as 25,000 !