Two PLATO Teledyne-e2v CCD280 have been proton irradiated: one whilst operating at cold and the other unbiased at room temperature. We report on differences in the postirradiation hot pixel population, trap species, and charge transfer inefficiency (CTI), including after annealing. We demonstrate once more that proton irradiation performed at the charge-coupled device temperature of operation can show significant differences to the traditional room-temperature irradiation. The cold-irradiated detector shows a factor 2 greater radiation induced increase in dark current and a factor 3 to 4 greater increase in hot pixel numbers, however, the parallel CTI measured in the PLATO operating conditions is a factor 1.5 lower. Using the trap pumping technique, we provide distributions of radiation-induced trap release time constants at different temperatures, which can be used to identify the type of defects and estimate CTI in other operating conditions.

Comparative Study of Cryogenic Versus Room-Temperature Proton Irradiation of N-Channel CCDs and Subsequent Annealing

PLATO { PLAnetary Transits and Oscillations of stars { is the third medium-class mission to be selected in the European Space Agency (ESA) Science and Robotic Exploration Cosmic Vision programme. Due for launch in 2025, the payload makes use of a large format (8 cm x 8 cm) Charge-Coupled Devices (CCDs) the e2v CCD270 operated at 4 MHz. The manufacture of such large device in large quantity constitutes an unprecedented effort. To de-risk the PLATO CCD procurement and aid the mission definition process, ESA's Payload Technology Validation team is characterizing the electro-optical performance of a number of PLATO devices before and after proton irradiation.

Technology validation of the PLATO CCD at ESA

The future ESA Earth Observation Sentinel-4/UVN is a high resolution spectrometer intended to fly on board a Meteosat Third Generation Sounder (MTG-S) platform, placed in a geostationary orbit. The main objective of this optical mission is to continuously monitor the air quality over Europe in near-real time. The Sentinel-4/UVN instrument operates in three wavelength bands: Ultraviolet (UV: 305-400 nm), Visible (VIS: 400- 500 nm) and Near-infrared (NIR: 750-775 nm). Two dedicated CCD detector have been developed to be used in the Focal Plane Subsystems (FPS), one for the combined UV and VIS band, the other covering the NIR band. Being a high resolution spectrometer with challenging radiometric accuracy requirements, both on spectral and spatial dimensions, an effect such the Random Telegraph Signal (RTS) can represent a relevant contribution for the complete system accuracy. In this work we analyze the RTS effect on data acquired during the FPS testing campaign with qualification models for the Sentinel-4/UVN detectors. This test campaign has been performed in late 2016. The strategy for the impact assessment of RTS is to measure the effect at room temperature and then to extrapolate the results to the at instrument operational temperature. This way, very-long lasting data acquisitions could be avoided since the RTS frequency is much lower at cryogenic temperatures. A reliable technique for RTS effect detection has been developed in order to characterize the signal levels amplitude and occurrence frequencies (flipping rate). We demonstrate the residual impact of the RTS on the global In-Orbit Sentinel-4/UVN instrument performance and products accuracy.

RTS effect detection in Sentinel-4 data

The exposure of Charge-Coupled Devices (CCD) to high-energy particles in space leads to a degradation of their performances. One of the observed mechanisms is the creation of defects in the CCD silicon lattice by displacement damage, inducing a reduction of the Charge Transfer Efficiency (CTE), i.e. the ability of the device to efficiently transfer the photo-induced charge to the read-out output node. Hence a reduction of the imaging quality of the detector. We present here a comparison of the modelled and measured optical quality of the FLEX CCD exposed to a high energy proton flux. The optical quality was directly measured on an irradiated flight representative device. A physical model of the detector, including an accurate modelling of the charge trapping dynamic, is used to generate synthetic scenes affected by CTE degradation from which the optical quality is assessed and compared to the measurement. Eventually the correlation of the model and the measurement will allow to accurately assess the performances of a detector exposed to space radiation environment.

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Proton-induced degradation of charge transfer efficiency on FLEX CCD detectors: measurement and impact on instrument performances

In the context of the technology validation of Charge-Coupled Devices for Euclid and PLATO, two European Space Agency missions dedicated to Astronomy, we present a comparison between the performance degradation (dark current and charge transfer inefficiency) after proton irradiation of two types of device manufactured by e2v

Performance Degradation after Proton Irradiation in Charge-Coupled Devices: A Cross-Device Comparison

Energetic particles in space damage electronic components, and in particular affect the capability of Charge-Coupled Devices (CCD) to transfer photo-generated charge packets to the output node. If not properly accounted for either during the instrument design process or in the mission data processing pipeline, radiation-induced Charge Transfer Inefficiency (CTI) causes image distortion, decreases the signal-to-noise ratio, and ultimately leads to bias in the measurement carried out. CTI is a well-identified error budget contributor for mission operating in the photon-starving regime like space telescopes dedicated to Astronomy, but is less studied in the context of Earth Observation missions. We present a study conducted during the Sentinel-4/UVN CCD pre-development to provide a first assessment of the CTI effects on the Sentinel-4 measurements.

H. Weber

Papers

Radiation-induced charge transfer inefficiency in charge-coupled devices: Sentinel-4 CCD pre-development as a case study