Operation of a THGEM-based detector in low-pressure Helium

Abstract

In view of a possible application as a charge-particle track readout for an Active Target Time Projection Chamber (AT-TPC), the operating properties of THick Gaseous Electron Multipliers (THGEM) in pure low-pressure Helium were investigated. This paper includes the effective gain dependence on pressure for different detector configurations (single-, double-, triple-cascade setup), long-term gain stability and energy resolution from tracks of 5.5 MeV alpha particles. Stable operational conditions and maximum detector gains of 10 4 -10 7 have been achieved in pure Helium at pressure ranging from 100 torr up to 760 torr. Energy resolution of 6.65% (FWHM) for 690 keV of energy deposited by 5.5 MeV alpha particles at 350 torr was measured. The expected energy resolution for the full track is around 2.4% (FWHM). These results, together with the robustness of THGEM electrodes against spark damage, make THGEM structures highly competitive compared to other technologies considered for TPC applications in an active target operating with pure noble gases, requiring a high dynamic range and a wide operating pressure range down to few hundred torr.

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

“…The experimental setup is conceptually similar to the one used in our previous study [6] and is schematically depicted in figure 1. It is composed of a 10x10 cm 2 THGEMs assembly, in single WELL-or double-THGEM cascade configurations, mounted in a single volume detector vessel of around 40 litres.…”

“…The THGEM used in this work and presented in the previous, related article [6], is based on avalanche multiplication in independent holes, arranged in a compact hexagonal array. The holes, with a 0.5 mm diameter are mechanically drilled in a copper-cladded double-sided 0.6 mm thick FR-4 plate, then the copper is etched to produce a 0.1 mm clearance from the holes' rim.…”

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].…”

Measurements of charging-up processes in THGEM-based particle detectors

“…The stability of the detector's gain over time is vital for reaching a stable performance of gasavalanche detectors, manifested in detector efficiency and energy resolution. Changes in the detector gain over the first hours of operation have been observed in gaseous detectors incorporating insulating electrode substrates; examples are in Gas Electron Multipliers (GEM) [1][2][3], Large Electron Multiplier (LEM) [4,5] and Thick Gaseous Electron Multiplier (THGEM) -based detectors [6][7][8][9][10][11]. The gain variation has been commonly attributed to charging-up of the detector's insulating surfaces that modifies the electric field in the charge-multiplication region.…”