Longitudinal profile of the charge cloud at high charge levels in Multi-Linear Silicon Drift Detectors for position-sensing applications

In this work we present the experimental qualification of the longitudinal profile of the charge cloud in Multi-Linear Silicon Drift Detectors at high charge levels. This is accomplished by means of a custom-developed deconvolution algorithm, based on the conjugate gradient method that extracts the actual shape of the anode current by deconvolution of the output waveforms of the frontend preamplifier response. We conducted two experimental campaigns, one with a pulsed IR laser system and one with mono-energetic proton bunches which allowed probing the detector response up at high charge levels (up to ~10⁶ electrons). At this level of charge injection Coulomb repulsion and plasma effects start to impact on the charge cloud dynamics and therefore on the detector speed as well as on the spatial resolution. The developed technique provides the true charge cloud profile without any a priori assumptions or model and is a powerful tool for diagnostics of the electron dynamics and for detector qualification in such operating conditions.