Cherenkov imaging counters requiring large photosensitive
areas, the capability to stand high rates and to operate
in magnetic field environments could benefit from the use of
micropattern gas detectors based on THick Gaseous Electron
Multiplier (THGEM) coupled to a solid state CsI photo-cathode.
Nevertheless, the ions produced in the charge multiplication
processes, which end up in the CsI photocathode Ion Back Flow
(IBF) compromise the detector performance: fast ageing of the
CsI photocathode, as well as electron extraction resulting in
spurious signals and eventual discharges can occur.
To avoid and limit these undesired events, several configurations
of THGEM based detectors were considered. Some changing
the whole detector geometry by changing the relative position
of individual THGEMs to take advantage of the microscopic diffusion properties of electrons and ions. One other configuration
changing directly the geometry of the THGEM itself to better
create an ion trap, the THCOBRA, is also studied.
In this work, experimental and simulation studies of these configurations
is performed, particularly concerning IBF and gain.
Finite element method calculations and Monte-Carlo simulations
are performed for a better understanding of the results.
