Advances in Thick GEM-like gaseous electron multipliers. Part II:   low-pressure operation
  We present results on THGEM operation at low gas pressures, in the range 0.5-50 Torr. Gaseous gain up to 100000 was recorded at 10 Torr of Isobutane in a single multiplier element, with pulses rise-time in the few ns range. Cascaded operation of two THGEMs is reported, with similar total gain but at lower voltages on each element. The present work encompasses a large variety of THGEM geometries and includes electric-field distribution calculations and electron transport simulations. We discuss the operation mechanism and some possible applications of THGEMs at low gas pressures. 
C.K. Shalem, R. Chechik, A. Breskin, K. Michaeli, N. Ben-Haim