Recent advances with THGEM detectors

Abstract

The Thick Gaseous Electron Multiplier (THGEM) is a simple and robust electrode suitable for large area detectors. In this work the results of extensive comparative studies of the physical properties of different THGEM-based structures are reviewed. The focus is on newly suggested THGEM-like WELL configurations as well as on recently developed characterization methods. The WELL structures are single-sided THGEM electrodes directly coupled to different anode readout electrodes. The structures differ by the coupling concept of the bottom THGEM electrode to the metallic readout pads: a Thick WELL (THWELL) with direct coupling; the Resistive WELL (RWELL) and the Segmented Resistive WELL (SRWELL) coupled through thin resistive films deposited on insulating sheets and a Resistive-Plate WELL (RPWELL) coupled through a plate of high bulk resistivity. The results are compared to that of traditional double-sided THGEM electrodes followed by induction gaps -in some cases with moderate additional multiplication within the gap. We compare the different configurations in terms of gain, avalanche extension, discharge-rate and magnitude as well as rate capabilities over a broad dynamic range -exploiting a method that mimics highly ionizing particles in the laboratory. We report on recent studies of avalanche distribution in THGEM holes using optical readout.

The Resistive-Plate WELL with Argon mixtures – A robust gaseous radiation detector

“…The lack of electrical instabilities over more than 10 8 pion events sets an upper limit of 10 −8 on the discharge probability -∼ 2 orders of magnitude better than other THGEM-based configurations (e.g. single-and double-THGEM, Resistive WELL and Segmented Resistive WELL reviewed in [7]).…”

“…[3,4]), including the use of resistive films and materials for reducing occasional discharge effects [5][6][7]. In this context, the experience gained with various configurations of THGEM-based multipliers with resistive anodes [7][8][9] has led to the development of a particularly promising candidate -the Resistive-Plate WELL (RPWELL) [10]. It is a single-sided copper-clad THGEM electrode, coupled to a segmented readout anode (pads or strips) through a thin high bulk-resistivity (∼10 8 -10 10 Ωcm) plate.…”

In-beam evaluation of a medium-size Resistive-Plate WELL gaseous particle detector

“…For all the rates investigated, the measured current is in agreement with the effective gain measured (figure 6-b); I = q · n · Φ · G(Φ), where I is the current, q is the electron charge, n is the number of electron-ion pairs produced by a minimum ionizing particle in 5 mm of Argon [19], Φ is the particle rate and G the detector gain (which depends on Φ as explained above). 6…”

“…These were operated in Ne/(5%CH 4 ) [4], and in Ar/(5%CH 4 ) and Ar/(7%CO 2 ) [5]. These and other studies of THGEMlike detectors (summarized in [6]), aimed at validating the potential applicability of the RPWELL as sampling element in digital hadron calorimetry (DHCAL). They have demonstrated dischargefree operation at high gas-avalanche gains, over a broad dynamic range.…”

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

“…Detailed measurements performed in a large range of pressure, from 100 torr to 760 torr, and with various detector configurations (single-, double-and triple-cascade THGEM detector) will be presented; in particular we discuss effective gains, long-term gain stability, and energy resolution from energy deposited by 5.5 MeV alpha particles, as well as future prospects. Figure 1 illustrates the various THGEM-based detector configurations used for effective gain measurements; they comprise either a single WELL-THGEM [22], [23], a double-or a triple-cascade elements with the last electrode in WELL configuration. Both, the single-and double-sided copper-clad THGEMs used throughout the present work have an effective area of 100 x 100 mm 2 , a thickness of 0.6 mm, a hole pitch of 0.7 mm, a hole diameter of 0.3 mm, and a rim around the holes of 0.1 mm.…”