  Tracking capabilities in Time Projection Chambers (TPCs) are strongly
dictated by the homogeneity of the drift field. Ion back-flow in various gas
detectors, mainly induced by the secondary ionization processes during
amplification, has long been known as a source of drift field distortion. Here,
we report on beam-induced space-charge effects from the primary ionization
process in the drift region in low-energy nuclear physics experiment with
Active Target Time Projection Chamber (AT-TPC). A qualitative explanation of
the observed effects is provided using detailed electron transport simulations.
As ion mobility is a crucial factor in the space-charge effects, the need for a
careful optimization of gas properties is highlighted. The impact of track
distortion on tracking algorithm performance is also discussed.
