Studies of THGEM-based detector at low-pressure Hydrogen/Deuterium, for AT-TPC applications

Abstract

We study the performance of single-and double-THick Gas Electron Multiplier (THGEM) detectors in pure Hydrogen (H2) and Deuterium (D2) at low pressures, in the range of 100-450 torr. The effect of the pressure on the maximum achievable gain, ion-back flow and long-term gain stability are investigated for single and double cascade detectors. In particular, it was found that maximum achievable gains above 10 4 , from single-photoelectrons avalanche, can be achieved for pressures of 200 torr and above; for lower pressure the gains are limited by avalanche-induced secondary effects to a values of around 10 3 . The results of this work are relevant in the field of avalanche mechanism in low-pressure, low-mass noble gases, in particular for applications of THGEM end-cap readout for active-target Time Projection Chambers (TPC) in the field of nuclear physics and nuclear astrophysics.

Simulation of gain stability of THGEM gas-avalanche particle detectors

“…Gain variations with time have been reported and are common in detectors containing dielectric materials in contact with the gas medium where multiplication occurs; the effects have been noticed particularly in detectors based on hole-type MPGDs with insulating surfaces in contact with active gases, e.g. Gas Electron Multipliers (GEMs) [1][2][3] and Thick-GEMs (THGEMs) [4][5][6][7][8][9][10].…”

Gain stabilization in Micro Pattern Gaseous Detectors: methodology and results

“…The phenomenon of avalanche-gain variations over time is well-known, particularly in Micro Pattern Gaseous Detectors (MPGD) incorporating insulator materials. It has been observed, for example, with Gas Electron Multipliers (GEM) [1-3], THick Gaseous Electron Multipliers (THGEM) [4,5] and other gas-avalanche amplifying structures [6][7][8]. These variations have been generally attributed to electric-field modifications resulting from "charging-up" effects of the insulator.…”

Recent advances with a hybrid micro-pattern gas detector operated in low pressure H2 and He, for AT-TPC applications

“…Following the encouraging results obtained in He with the small-area, test-bench detector [14][15], two large THGEM electrodes (270 mm diameter) have been commissioned and assembled on the pAT-TPC endcap plane (Figure 4). The performance evaluation and characterization of the new hybrid endcap detector have been performed in H2, at a pressure of 200 and 300 torr ( Figure 5 and 6, respectively).…”

“…A maximum achievable gain of around 30 was measured at 760 torr, while for lower pressure the value decreases to less than 10 for pressure below 500 torr. In order to achieve a suitable gas gain during operation with pure low-mass noble gas, the Micromegas readout was combined with pre-amplification stages based on the hole-type THGEM multiplier [14]. This hybrid configuration allow to cascade many multiplier elements and to obtain an overall higher effective gain by manifold electron avalanche processes.…”

“…This hybrid configuration allow to cascade many multiplier elements and to obtain an overall higher effective gain by manifold electron avalanche processes. Furthermore, THGEM-based detectors permit stable operation at high gain in pure noble gas at low pressure due to [13][14][15]: -) the extended dimension of the THGEM holes, typically several times larger than the electron mean-free path even at low pressure; -) the confinement of the avalanche within the holes, resulting in smaller photon-mediated secondary effects; -) the quenching effect of small amounts of impurity from natural outgassing of detector components -e.g. N2 acts as wavelength shifter suppressing UV-photons emitted during the avalanche.…”