  The ALICE experiment at LHC has planned to upgrade the TPC by replacing the
MWPC with GEM based detecting elements to restrict the IBF to a tolerable
value. However the variation of the gain as a function of physical parameters
of industrially produced large size GEM foils is needed to be studied as a part
of the QA procedure for the detector. The size of the electron avalanche and
consequently the gain for GEM based detectors depend on the electric field
distribution inside the holes. Geometry of a hole plays an important role in
defining the electric field inside it. In this work we have studied the
variation of the gain as a function of the hole diameters using Garfield++
simulation package.
