Electron transport and electric field simulations in two-phase detectors with THGEM electrodes

Abstract

One of the main features of two-phase detectors with electroluminescence (EL) gap being developed in our laboratory for dark matter search is the extensive use of THGEMs (Thick Gas Electron Multipliers). In various versions of the detector, the THGEMs are used as electrodes in the gas and liquid phases to form the drift, electron emission and EL regions, as well as for avalanche amplification of a signal in the gas phase. In this work the simulations of the electric field and electron transport through such THGEM electrodes were performed. In the liquid phase, these simulations allowed to determine the optimal parameters, such as the hole diameter of THGEM and applied voltage across it, that can provide effective transmission of the electrons from the drift region to that of the EL gap. In the gas phase, the effect of the THGHEM voltage on the electric field uniformity in the EL gap was studied. Structure of the THGEM-based two-phase detectorThe generalized version of the two-phase detector with EL gap used in our current studies [3,4,6,9] is shown in Fig. 1. To form the drift, electron emission and electroluminescence

SiPM-matrix readout of two-phase argon detectors using electroluminescence in the visible and near infrared range

“…THGEM0 was biased in a way to provide a transmission of drifting electrons from the drift region to that of electron emission: the electrons drifted successively from a lower to higher electric field region. The electron transmission efficiency, defined by the voltage applied across THGEM0 and its geometrical parameters, was calculated in [34] to be 62%.…”

Electroluminescence and Electron Avalanching in Two-Phase Detectors

“…The feature of such a THGEM interface grid is that one must apply a high enough voltage across it to have the 100% electron transmittance. In particular, in liquid Ar, for the THGEM electrode with 28% optical transparency the nominal electric field should exceed 5 kV/cm to provide the 100% electron transmission [79]: see Figure 21, right. On the other hand, it was shown there that the THGEM with 75% optical transparency provides 100% electron transmission at already 2 kV/cm of nominal electric field.…”

“…The advantage of such THGEM electrodes compared to wire electrodes is that they are quite rigid which avoids the problem of wire grid sagging under high electric field in large-area two-phase detectors. [9,12]: with 28% (a) and 75% (b) optical transparency (from [79], with permission from Elsevier). Right: calculated electron transmission through 28% THGEM acting as an interface grid immersed in liquid Ar as a function of the voltage across THGEM (bottom axis) and nominal electric field in THGEM (top axis) (from [79], with permission from Elsevier).…”

“…The earlier works on realizing this concept in two-phase Ar [55] and Xe [56] detectors should be mentioned, albeit with smaller active area and SiPM matrix size. [79], with permission from Elsevier). The electric fields below and above the THGEM were 0.56 and 4.3 kV/cm respectively.…”

“…Figure21. Left: microscope images of two THGEM electrodes used as interface grids in two-phase Ar detectors in[9,12]: with 28% (a) and 75% (b) optical transparency (from[79], with permission from Elsevier). Right: calculated electron transmission through 28% THGEM acting as an interface grid…”