M. Pitt

THGEM-based detectors for sampling elements in DHCAL: laboratory and beam evaluation

We report on the results of an extensive R&}D program aimed at the evaluation of Thick-Gas Electron Multipliers (THGEM) as potential active elements for Digital Hadron Calorimetry (DHCAL). Results are presented on efficiency, pad multiplicity and discharge probability of a 10x10 cm2 prototype detector with 1 cm2 readout pads. The detector is comprised of single- or double-THGEM multipliers coupled to the pad electrode either directly or via a resistive anode. Investigations employing standard discrete electronics and the KPiX readout system have been carried out both under laboratory conditions and with muons and pions at the CERN RD51 test beam. For detectors having a charge-induction gap, it has been shown that even a ~ 6 mm thick single-THGEM detector reached detection efficiencies above 95%, with pad-hit multiplicity of 1.1?1.2 per event; discharge probabilities were of the order of 10?6-10?5 sparks/trigger, depending on the detector structure and gain. Preliminary beam tests with a WELL hole-structure, closed by a resistive anode, yielded discharge probabilities of < 2x10?6 for an efficiency of ~ 95%. Methods are presented to reduce charge-spread and pad multiplicity with resistive anodes. The new method showed good prospects for further evaluation of very thin THGEM-based detectors as potential active elements for DHCAL, with competitive performances, simplicity and robustness. Further developments are in course.

Beam studies of the segmented resistive WELL: a potential thin sampling element for digital hadron calorimetry

Thick Gas Electron Multipliers (THGEMs) have the potential of constituting thin, robust sampling elements in Digital Hadron Calorimetry (DHCAL) in future colliders. We report on recent beam studies of new single- and double-THGEM-like structures; the multiplier is a Segmented Resistive WELL (SRWELL) - a single-faced THGEM in contact with a segmented resistive layer inductively coupled to readout pads. Several 10 10 cm 2 configurations with a total thickness of 5-6 mm (excluding electronics) with 1 cm 2 pads coupled to APV-SRS readout were investigated with muons and pions. Detection e ciencies in the 98% range were recorded with average pad-multiplicity of 1.1. The resistive anode resulted in e cient discharge damping, with potential drops of a few volts; discharge probabilities were 10 7 for muons and 10 6 for pions in the double-stage configuration, at rates of a few kHz/cm 2 . Further optimization work and research on larger detectors are underway.

Beam studies of novel THGEM-based potential sampling elements for Digital Hadron Calorimetry

Beam studies of thin single- and double-stage THGEM-based detectors are presented. Several 10 x 10 cm^2 configurations with a total thickness of 5-6 mm (excluding readout electronics), with 1 x 1 cm^2 pads inductively coupled through a resistive layer to APV-SRS readout electronics, were investigated with muons and pions. Detection efficiencies in the 98% range were recorded with an average pad-multiplicity of ~1.1. The resistive anode resulted in efficient discharge damping, with few-volt potential drops; discharge probabilities were ~10^{-7} for muons and 10^{-6} for pions in the double-stage configuration, at rates of a few kHz/cm^2. These results, together with the robustness of THGEM electrodes against spark damage and their suitability for economic production over large areas make THGEM-based detectors highly competitive compared to the other technologies considered for the SiD-DHCAL.

Laboratory studies of THGEM-based WELL structures with resistive anode

In this work we investigate three variants of single amplification-stage detector elements; they comprise THGEM electrodes closed at their bottom with metallic or resistive anodes to form WELL-type configurations. We present the results of a comparative study of the Thick-WELL (THWELL), Resistive-WELL (RWELL) and Segmented Resistive WELL (SRWELL), focusing on their performance in terms of spark-quenching capability, gain variation with position and counting rate, pulse shapes and signal propagation to neighboring readout pads; the study included both 30x30 and 100x100 mm

Optical readout: a tool for studying gas-avalanche processes

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Recent advances with THGEM detectors

detectors. It was shown that the WELL structures with resistive anodes offer stable operation even in a highly ionizing environment, with effective spark quenching, as well as higher gain than the standard THGEM/induction-gap configuration. Cross talk between neighboring readout pads was shown to be effectively eliminated in the segmented detector with a conductive grid underneath the resistive layer. The latter multiplier should allow for the design of very thin detectors, e.g. sampling elements in digital hadronic calorimeters planned for experiments in future linear colliders.

First in-beam studies of a Resistive-Plate WELL gaseous multiplier

Optical recording of avalanche-induced photons is an interesting tool for studying basic physics processes in gaseous detectors. In this work we demonstrate the potential of optical readout in avalanche-propagation investigations in Thick Gas Electron Multipliers (THGEMs) operated with Ne/CF4 (95/5). We present the results of direct measurements with single- and cascaded-THGEM detectors irradiated with soft x-rays, of the hole-multiplicity and avalanche asymmetry within holes as a function of detector parameters. Further study directions are discussed.

First results with THGEM followed by submillimetric multiplying gap

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; they differ by the coupling concept of the bottom THGEM electrode to the metallic readout pads. 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.

A concept for laboratory studies of radiation detectors over a broad dynamic-range: instabilities evaluation in THGEM-structures

We present the results of the first in-beam studies of a medium size (10 × 10 cm 2 ) Resistive-Plate WELL (RPWELL): a single-sided THGEM coupled to a pad anode through a resistive layer of high bulk resistivity (~109 Ωcm). The 6.2 mm thick (excluding readout electronics) single-stage detector was studied with 150 GeV muons and pions. Signals were recorded from 1×1 cm 2 square copper pads with APV25-SRS readout electronics. The single-element detector was operated in Ne/(5%CH4) at a gas gain of a few times 104 , reaching 99% detection efficiency at average pad multiplicity of ~1.2. Operation at particle fluxes up to ~104 Hz/cm 2 resulted in ~23% gain drop leading to ~5% efficiency loss. The striking feature was the discharge-free operation, also in intense pion beams. These results pave the way towards robust, efficient large-scale detectors for applications requiring economic solutions at moderate spatial and energy resolutions.

arXiv : Simulation of gain stability of THGEM gas-avalanche particle detectors

This work presents the first results dealing with THGEMs coupled to submillimetric multiplication gaps, operated in an atmospheric pressure of Ne/CF4. The experimental studies done so far with a THGEM coupled to submillimetric multiplication gaps achieved charge-gains of 4 × 104 and 1 × 105 in Ne/CF4 (95:5), for 0.4 mm and 0.8 mm gaps, respectively, values that are one order of magnitude higher than those obtained in single-THGEM configuration and approximately half from those obtained for a cascaded-THGEM configuration. The present studies evaluate the performance operation in terms of the charge-gain characteristics and X-ray energy resolution.