Performance characterization of UV science cameras developed for the Chromospheric Lyman-Alpha Spectro-Polarimeter (CLASP)

Abstract

The NASA Marshall Space Flight Center (MSFC) has developed a science camera suitable for sub-orbital missions for observations in the UV, EUV and soft X-ray. Six cameras will be built and tested for flight with the Chromospheric Lyman-Alpha Spectro-Polarimeter (CLASP), a joint National Astronomical Observatory of Japan (NAOJ) and MSFC sounding rocket mission. The goal of the CLASP mission is to observe the scattering polarization in Lyman-α and to detect the Hanle effect in the line core. Due to the nature of Lyman-α polarization in the chromosphere, strict measurement sensitivity requirements are imposed on the CLASP polarimeter and spectrograph systems; science requirements for polarization measurements of Q/I and U/I are 0.1% in the line core. CLASP is a dual-beam spectro-polarimeter, which uses a continuously rotating waveplate as a polarization modulator, while the waveplate motor driver outputs trigger pulses to synchronize the exposures. The CCDs are operated in frame-transfer mode; the trigger pulse initiates the frame transfer, effectively ending the ongoing exposure and starting the next. The strict requirement of 0.1% polarization accuracy is met by using frametransfer cameras to maximize the duty cycle in order to minimize photon noise. The CLASP cameras were designed to operate with ≤ 10 e − /pixel/second dark current, ≤ 25 e − read noise, a gain of 2.0 +-0.5 and ≤ 1.0% residual non-linearity. We present the results of the performance characterization study performed on the CLASP prototype camera; dark current, read noise, camera gain and residual non-linearity.

X-ray evaluation of the Marshall Grazing Incidence X-ray Spectrometer (MaGIXS) nickel-replicated mirrors

“…The MSFC developed CCD detector will detect the first-order diffraction. 4,5 The stigmatic optical design gives good performance on and off-axis, out to a 4 arcminute field angle. The desired performance across the full field is 6 arcsecond angular resolution, and ∼ 22 mÅ (7.5 -0.47 eV) spectral resolution.…”

Indication of the Hanle Effect by Comparing the Scattering Polarization Observed by CLASP in the Lyα and Si iii 120.65 nm Lines

“…The equations to derive s phot and s CCD are the ones in Appendices A.1 and A.2 of Ishikawa et al (2014b). We employ an averaged read-out noise of sixelectrons (Champey et al 2014(Champey et al , 2015, which correspond to sixphotons. The averaged uncertainty is 0.066% at the Lyα core, 0.18% at the Lyα wing, and 0.50% at the Si III line.…”

Polarization Calibration of the Chromospheric Lyman-Alpha SpectroPolarimeter for a 0.1% Polarization Sensitivity in the VUV Range. Part II: In-Flight Calibration

“…The photon noise was calculated as the square root of the number of photoelectrons. The read-out noise was calculated based on the CCD calibration results of 6.2 and 6.5 e − rms per pixel for channel 1 and channel 2, respectively (Champey et al, 2014(Champey et al, , 2015. Variations of the signal larger than the noise can be seen in the wings, which indicate that the fluctuations from solar origin polarization might not be entirely cancelled out there.…”