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Since the launch of ESA's Gaia satellite in December 2013, the 106large-format scientific CCDs onboard have been operating at L2. Due to acombination of the high-precision measurement requirements of the mission andthe predicted proton environment at L2, the effect of non-ionizing radiationdamage on the detectors was early identified pre-launch as potentially imposinga major limitation on the scientific value of the data. In this paper wecompare pre-flight radiation-induced Charge Transfer Inefficiency (CTI)predictions against in-flight measurements, focusing especially on chargeinjection diagnostics, as well as correlating these CTI diagnostic results withsolar proton event data. We show that L2-directed solar activity has beenrelatively low since launch, and radiation damage (so far) is less thanoriginally expected. Despite this, there are clear cases of correlation betweenearth-directed solar coronal mass ejection events and abrupt changes in CTIdiagnostics over time. These sudden jumps are lying on top of a rather constantincrease in CTI which we show is primarily due to the continuous bombardment ofthe devices by high-energy Galactic Cosmic Rays. We examine the possiblereasons for the lower than expected levels of CTI as well as examining theeffect of controlled payload heating events on the CTI diagnostics.Radiation-induced CTI in the CCD serial registers and effects of ionizingradiation are also correspondingly lower than expected, however these topicsare not examined here in detail.

Radiation effects on the Gaia CCDs after 30 months at L2