The THGEM: A thick robust gaseous electron multiplier for radiation detectors

A. Breskin, M. Cortesia , R. Alon, J. Miyamoto a, V. Peskov a, G. Bartesaghi, a R. Chechika, V. Dangendorf b , J. M. Maia c, J.M.F. dos Santos d

a Weizmann Institute of Science, Rehovot, IsraelbPTB, Braunshweig, GermanycUniversity of Beira-Interior, Covilha, PortugaldPhysics Department, University of Coimbra, Portugal

Presented by

HOPE EARL R. BORONGAN

OutlineIntroduction Motivation Objective

Principal Properties of THGEM detectors

Applications

Introduction

MotivationThe development of the Thick Gas Electron Multiplier (THGEM) was motivated by the need for robust large –area, fast radiation imaging detectors with moderate localization resolution.

-by choosing the the electrode’s functional-structure dimensions in the sub-mm scale, relatively simple and inexpensive production techniques can be employed to porduce very large-area detectors.

- A sub-mm distance between anode and cathode ensures fas charge collection and timing of a few ns; yet, the sub-mm hole diameter is larger than electron diffusion in most gases, with consequently favorable electron transport into and out of the holes.

Objective

We Briefly summarize here the principal detector properties, present recent data on THGEM operation in noble gases and discuss applications in particle physics and beyond.

The THGEM is produced from metal-clad insulator by drilling holes and etching their rims. The latter enhance the electrode’s immunity to defect-induced discharges, leading to higher gains compared to rimless holes. The rim is most probaby responsible for up-charging and polarization of the substrate, manifested as long stabilization time of the detector’s gain.

FIGURE 1

PRINCIPAL DETECTOR PROPERTIES

FIGURE 3a

In Ne and Ne/CH4 mixtures, very high gains were reached at rather low voltages.

Importantly, in Ar/5%CH4 the gain limit for 9keV X-rays is about 50 times lower than that for single photoelectrons, assumed to e a charge density effect; in Ne and Ne/CH4 mixtures a significantly smaller difference in gain limit was noted in coherence with the lower ionization charge density.

FIGURE 3b

Fig. 4 Gain of single and double THGEMs in Xe and Xe/5% Ar at various pressures, room temperature.

Applications

THGEM detectors could be considered for applications where robust, economic, large-area detectors are required, with fast response and sub-mm resolution.They are also good candidates when operation in noble gases is foreseen.

Presently, they are studied as an optional upgrade of the photon detectors of the CERN-COMPASS and CERN-ALICE RICH systems. A double or a triple-THGEM imaging detector with reflective CsI photocathode deposited on the 1st THGEM-s top electrode is envisaged within the CERN RD51 project.

Track sampling in digital calorimeters at the future ILC

Applications

THGEM-photomultipliers with CsI photocathodes are investigated for a novel LXe γ-camera, for a 3- γ medical-imaging concept.THGEM could be used for neutron radiography, by coupling them to appropriate converters.

The stable high gain operation of THGEM detectors in most noble gases at temperatures down to the LAr, make them attractive candidates for applications in various double-phase detectors or large TPC’s, designed for rare-event experiments (dark matter, neutrino physics, double-beta decay, etc)

THGEM detectors with CsI photocathodes may also record scintillation light from interactions in the liquid or the gas phases, as well as electrons deposited in the TPC volume.