  In view of a possible application as a charge-particle track readout for an
Active-Target Time Projection Chamber (AT-TPC), the operational properties and
performances of a hybrid Micro-Pattern Gaseous Detector (MPGD) were
investigated in pure low-pressure Hydrogen (H2) and Helium (He). The detector
consists of a MICROMesh GAseous Structure (MICROMEGAS) coupled to a single- or
multi-cascade THick Gaseous Electron Multiplier (THGEM) as a pre-amplification
stage. This study reports of the effective gain dependence of the hybrid-MPGD
at relevant pressure (in the range of 200-760 torr) for different detector
arrangements. The results of this work are relevant in the field of avalanche
mechanism in low-pressure, low-mass noble gases, in particularly for
applications of MPGD end-cap readout for active-target Time Projection Chambers
(TPC) in the field of nuclear physics and nuclear astrophysics.
