Multi-layer Thick Gas Electron Multiplier (M-THGEM): a new MPDG   structure for high-gain operation at low-pressure
  The operating principle and performances of the Multi-layer Thick Gaseous Electron Multiplier (M-THGEM) is presented. The M-THGEM is a novel hole-type gaseous electron multiplier produced by multi-layer printed circuit board technology; it consists of a densely perforated assembly of multiple insulating substrate sheets (e.g., FR-4), sandwiched between thin metallic-electrode layers. The electron avalanche processes occur along the successive multiplication stages within the M-THGEM holes, under the action of strong dipole fields resulting from the application of suitable potential differences between the electrodes. The present work focuses on investigation of two different geometries: a two-layer M-THGEM (either as single or double-cascade detector) and a single three-layer M-THGEM element, tested in various low-pressure He-based gas mixtures. The intrinsically robust confinement of the avalanche volume within the M-THGEM holes provides an efficient suppression of the photon-induced secondary effects, resulting in a high-gain operation over a broad pressure range, even in pure noble gas. The operational principle, main properties (maximum achievable gain, long-term stability, energy resolution, etc.) under different irradiation conditions, as well as capabilities and potential applications are discussed. 
M. Cortesi, S. Rost, W. Mittig, Y. Ayyad Limonge, D. Bazin, J. Yurkon,   and A. Stolz
physics.ins-det