  The present $\mathrm{R}\&\mathrm{D}$ activities for the International Large
Detector Time Projection Chamber (ILD-TPC) concern the adoption of the micro
pattern devices for the gaseous amplification stage. Seven Micromegas modules
which are commissioned on the end-plate of a Large Prototype TPC (LPTPC) at
DESY, were tested with a 5 GeV electron beam, under a 1 T magnetic field.
During experiments, reduced signal sensitivity as well as distortion in the
reconstructed track was observed at the boundaries of these modules.
Electrostatic field inhomogeneity near the module boundaries was considered to
be the possible major reason behind these observations. In the present work,
this hypothesis has been explored using the Garfield simulation framework. It
has been possible to contain the computational complexity of the problem with
suitable simplifications. Qualitative and quantitative agreements with
experimental results have been achieved. Possibility of mitigating the problems
has been proposed using the same simulation framework.

Instrumentation and Detectors;High Energy Physics - Experiment