Studying unstable nuclei away from the line of stability using low energy reactions is of high interest in modern nuclear physics. The low energy ions observed in these reactions lose most of their energy within the target, therefore the construction of an Active Target Time Projection Chamber (AT-TPC), detecting the track within the target, is an attractive solution. In order to maximize the reaction yield while minimizing background operation in pure gas without quench gas is necessary. In pure gas, however, the transition to streamer mode (discharge) occurs already at low gain when using common structures (e.g. GEM (gas electron multiplier)), therefore a new type of detector functioning at high gain in pure elemtal gas is required. Two THick Gaseous Electron Multipliers (THGEM) in cascade were found to operate at a gain of up to 10^4 in pure helium for pressures between 200 torr and 600 torr, while also providing a good energy resolution. The THGEM is a hole-type gaseous electron multiplier produced by multilayer printed circuit board (PCB) technology. It consists of a densely perforated assembly of 0.6mm thick FR-4 substrate, sandwiched between thin metallic electrode strata. Three THGEMs were stacked together to form a novel gaseous multiplier (M-THGEM), providing a high confinement of the electron avalanche within the hole, resulting in a gain of up to 10^4.5 in pure low-pressure helium. It demonstrated a very good energy resolution in the experiment and an estimated ion backflow of as low as 13% in simulations. Furthermore, it is extremely suitable to cover large areas due to its robustness, making the three layer M-THGEM suitable for a large detector such as the AT-TPC.
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