Avalanche-ion back-flow reduction in gaseous electron multipliers based on GEM/MHSP

Abstract

We report on avalanche-ion back-flow measurements in the novel Micro-Hole and Strip-Plate (MHSP) multiplier and in gaseous photomultipliers comprising Gas Electron Multipliers (GEMs) followed by an MHSP. In a 3-GEMs/ MHSP photomultiplier with reflective photocathode, avalanche-ion back-flow fraction of B7% and B2% were recorded for respective effective gains of 10 7 and 10 6 , in Ar/CH 4 (95/5) at 760 Torr. This is about one order of magnitude reduction in ion back-flow compared to the best values measured in 4-GEMs photomultiplier at the same gain. We describe the mode of operation of the MHSP and explain its ion back-flow reduction features. r

The Photon-Assisted Cascaded Electron Multiplier: a concept for potential avalanche-ion blocking

“…From [23] we know that the ions produced in the anode-strip avalanche are partly collected on the neighbouring cathode strips and partly on the cathode mesh below the MHSP. Thus, for an induction field of -5kV/cm, a residual 20% fraction of ions (and up to 40% at -1kV/cm) will go back into the MHSP holes (see figure 6 in [23]).…”

MHSP in reversed-bias operation mode for ion blocking in gas-avalanche multipliers

“…In the second multiplication step at the anode strips, the ions' and electron' paths split, and a significant part of the ions is collected on the neighboring cathode strips and on the cathode plane placed below the MHSP. Thus, when the MHSP was used as a last element in the cascade, following three GEMs, a further reduction of the IBF to $2-3%, at effective gains o 10 5 -10 6 , was reported [18,19].…”

Recent advances in X-ray detection with micro-hole and strip plate detector

“…An important additional advantage of this design is the significant reduction of photon feedback and avalanche-ion back-flow, discussed in detail in Refs. [10][11][12]. The multiplication properties of MHSPs and of cascaded multi-GEM and MHSP have been systematically investigated in Refs.…”