Setup and Characteristics of a Timing Reference Signal with sub-ps Accuracy for AWAKE

We describe a method to overcome the triggering jitter of a streak camera to obtain less noisy images of a self-modulated proton bunch over long time scales (~ 400 ps to ns) with the time resolution (~ 1 ps) of the short time scale images (73 ps). We also determine that this method, using a reference laser pulse with a variable delay, leads to the determination of the time delay between the ionizing laser pulse and the reference pulse with an error of 0.6 ps (rms).