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Proceedings Paper

Cryogenic irradiation of an EMCCD for the WFIRST coronagraph: preliminary performance analysis
Author(s): Nathan Bush; David Hall; Andrew Holland; Ross Burgon; Neil Murray; Jason Gow; Douglas Jordan; Richard Demers; Leon K. Harding; Bijan Nemati; Michael Hoenk; Darren Michaels; Pavani Peddada
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Paper Abstract

The Wide Field Infra-Red Survey Telescope (WFIRST) is a NASA observatory scheduled to launch in the next decade that will settle essential questions in exoplanet science. The Wide Field Instrument (WFI) offers Hubble quality imaging over a 0.28 square degree field of view and will gather NIR statistical data on exoplanets through gravitational microlensing. An on-board coronagraph will for the first time perform direct imaging and spectroscopic analysis of exoplanets with properties analogous to those within our own solar system, including cold Jupiters, mini Neptunes and potentially super Earths.

The Coronagraph Instrument (CGI) will be required to operate with low signal flux for long integration times, demanding all noise sources are kept to a minimum. The Electron Multiplication (EM)-CCD has been baselined for both the imaging and spectrograph cameras due its ability to operate with sub-electron effective read noise values with appropriate multiplication gain setting. The presence of other noise sources, however, such as thermal dark signal and Clock Induced Charge (CIC), need to be characterized and mitigated. In addition, operation within a space environment will subject the device to radiation damage that will degrade the Charge Transfer Effciency (CTE) of the device throughout the mission lifetime. Irradiation at the nominal instrument operating temperature has the potential to provide the best estimate of performance degradation that will be experienced in-flight, since the final population of silicon defects has been shown to be dependent upon the temperature at which the sensor is irradiated.

Here we present initial findings from pre- and post- cryogenic irradiation testing of the e2v CCD201-20 BI EMCCD sensor, baselined for the WFIRST coronagraph instrument. The motivation for irradiation at cryogenic temperatures is discussed with reference to previous investigations of a similar nature. The results are presented in context with those from a previous room temperature irradiation investigation that was performed on a CCD201-20 operated under the same conditions. A key conclusion is that the measured performance degradation for a given proton fluence is seen to measurably differ for the cryogenic case compared to the room temperature equivalent for the conditions of this study.

Paper Details

Date Published: 5 August 2016
PDF: 18 pages
Proc. SPIE 9915, High Energy, Optical, and Infrared Detectors for Astronomy VII, 99150A (5 August 2016); doi: 10.1117/12.2234628
Show Author Affiliations
Nathan Bush, The Open Univ. (United Kingdom)
David Hall, The Open Univ. (United Kingdom)
Andrew Holland, The Open Univ. (United Kingdom)
Ross Burgon, The Open Univ. (United Kingdom)
Neil Murray, The Open Univ. (United Kingdom)
Jason Gow, The Open Univ. (United Kingdom)
Douglas Jordan, e2v technologies (UK) Ltd. (United Kingdom)
Richard Demers, Jet Propulsion Lab. (United States)
Leon K. Harding, Jet Propulsion Lab. (United States)
Bijan Nemati, Jet Propulsion Lab. (United States)
Michael Hoenk, Jet Propulsion Lab. (United States)
Darren Michaels, Jet Propulsion Lab. (United States)
Pavani Peddada, Jet Propulsion Lab. (United States)

Published in SPIE Proceedings Vol. 9915:
High Energy, Optical, and Infrared Detectors for Astronomy VII
Andrew D. Holland; James Beletic, Editor(s)

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