Technology advancement of the CCD201-20 EMCCD for the WFIRST coronagraph instrument: sensor characterization and radiation damage

摘要

The Wide Field InfraRed Survey Telescope-Astrophysics Focused Telescope Asset(WFIRST-AFTA) mission is a 2.4-m class space telescope that will be used acrossa swath of astrophysical research domains. JPL will provide a high-contrastimaging coronagraph instrument - one of two major astronomical instruments. Inorder to achieve the low noise performance required to detect planets underextremely low flux conditions, the electron multiplying charge-coupled device(EMCCD) has been baselined for both of the coronagraph's sensors - the imagingcamera and integral field spectrograph. JPL has established an EMCCD testlaboratory in order to advance EMCCD maturity to technology readiness level-6.This plan incorporates full sensor characterization, including read noise, darkcurrent, and clock-induced charge. In addition, by considering the uniquechallenges of the WFIRST space environment, degradation to the sensor's chargetransfer efficiency will be assessed, as a result of damage from high-energyparticles such as protons, electrons, and cosmic rays. Science-grade CCD201-20EMCCDs have been irradiated to a proton fluence that reflects the projectedWFIRST orbit. Performance degradation due to radiation displacement damage isreported, which is the first such study for a CCD201-20 that replicates theWFIRST conditions. In addition, techniques intended to identify and mitigateradiation-induced electron trapping, such as trap pumping, custom clocking, andthermal cycling, are discussed.