In recent years, the near detector of the T2K experiment underwent an important upgrade of part of its equipment, which involved the construction of a set of new instruments. As a part of the upgrade, two gaseous TPCs, placed above and below the active target, will enable the study of particles generated at large angles by neutrino interactions. Each High Angle TPC (HA-TPC) includes a large active volume defined by rectangular cross-section Field Cages with lightweight composite material walls and two readout planes instrumented with eight Resistive Micromegas each. 
A deep knowledge of this detector is crucial to achieve good performance. This communication reports the studies that are being carried out in order to get a deep comprehension of the signal formation in an ERAM detector operating with the T2K gas mixture; in particular, the aim of the study is to determine the effect of the ions on the electron spread in the resistive layer and the consequent electric signal generation. Preliminary studies have been carried out on non-resistive Micromegas to determine the ion drift velocity in the T2K gas mixture; experimental data are compared with the results of a dedicated Monte Carlo simulation.

ERAM,Micromegas,tpc,DLC