An Analytical Model of Radiation-Induced Charge Transfer Inefficiency for CCD Detectors

TL;DR

This paper presents a physically realistic, efficient analytical model of radiation-induced charge transfer inefficiency in CCD detectors, crucial for calibrating data in space missions like Gaia and Euclid.

Contribution

The paper introduces a generalized, fast analytical model of radiation damage effects on CCD charge transfer, applicable to space missions with high-precision requirements.

Findings

Model accurately predicts charge distortion effects.

Applicable to Gaia and Euclid missions.

Enables efficient calibration of radiation damage effects.

Abstract

The European Space Agency's Gaia mission is scheduled for launch in 2013. It will operate at L2 for 5 years, rotating slowly to scan the sky so that its two optical telescopes will repeatedly observe more than one billion stars. The resulting data set will be iteratively reduced to solve for the position, parallax and proper motion of every observed star. The focal plane contains 106 large area silicon CCDs continuously operating in a mode where the line transfer rate and the satellite rotation are in synchronisation. One of the greatest challenges facing the mission is radiation damage to the CCDs which will cause charge deferral and image shape distortion. This is particularly important because of the extreme accuracy requirements of the mission. Despite steps taken at hardware level to minimise the effects of radiation, the residual distortion will need to be calibrated during the pipeline data processing. Due to the volume and inhomogeneity of data involved, this requires a model which describes the effects of the radiation damage which is physically realistic, yet fast enough to implement in the pipeline. The resulting charge distortion model was developed specifically for the Gaia CCD operating mode. However, a generalised version is presented in this paper and this has already been applied in a broader context, for example to investigate the impact of radiation damage on the Euclid dark-energy mission data.