  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 across
a swath of astrophysical research domains. JPL will provide a high-contrast
imaging coronagraph instrument - one of two major astronomical instruments. In
order to achieve the low noise performance required to detect planets under
extremely low flux conditions, the electron multiplying charge-coupled device
(EMCCD) has been baselined for both of the coronagraph's sensors - the imaging
camera and integral field spectrograph. JPL has established an EMCCD test
laboratory in order to advance EMCCD maturity to technology readiness level-6.
This plan incorporates full sensor characterization, including read noise, dark
current, and clock-induced charge. In addition, by considering the unique
challenges of the WFIRST space environment, degradation to the sensor's charge
transfer efficiency will be assessed, as a result of damage from high-energy
particles such as protons, electrons, and cosmic rays. Science-grade CCD201-20
EMCCDs have been irradiated to a proton fluence that reflects the projected
WFIRST orbit. Performance degradation due to radiation displacement damage is
reported, which is the first such study for a CCD201-20 that replicates the
WFIRST conditions. In addition, techniques intended to identify and mitigate
radiation-induced electron trapping, such as trap pumping, custom clocking, and
thermal cycling, are discussed.
