  The operation of gas detectors is often limited by secondary effects,
originating from avalanche-induced photons and ions. Ion backflow is one of the
effects limiting the operation of a gas detector at high flux, by giving rise
to space charge which disturbs the electric field locally. For the Micromegas
detector, a large fraction of the secondary positive ions created in the
avalanche can be stopped at the micro-mesh. The present work involves
measurements of the ion backflow fraction (using an experimental setup
comprising of two drift planes) in bulk Micromegas detectors as a function of
detector design parameters. These measured characteristics have also been
compared in detail to numerical simulations using the Garfield framework that
combines packages such as neBEM, Magboltz and Heed. Further, the effect of
using a second micro-mesh on ion backflow and other parameters has been studied
numerically.
