Thick Gas Electron Multiplier Research Articles

Scintillation of Ar/CF4 mixtures: glass-THGEM characterization with 1% CF4 at 1–1.5 bar

Argon gas doped with 1% wavelength-shifter (CF4) has been employed in an optical time projection chamber (OTPC) to image cosmic radiation. We present results obtained during the system commissioning, performed with two stacked glass thick gaseous electron multipliers (THGEMs) and an electron-multiplying charge coupled device (EMCCD camera) at 1 bar. Preliminary estimates indicate that the combined optical gain was of the order of 106 (ph/e), producing sharp and high-contrast raw images without resorting to any filtering or post-processing. A first assessment of the impact of pressurization showed no change in the attainable gains when operating at 1.5 bar.

Charge amplification in sub-atmospheric CF4:He mixtures for directional dark matter searches

Low pressure gaseous Time Projection Chambers (TPCs) are a viable technology for directional Dark Matter (DM) searches and have the potential for exploring the parameter space below the neutrino fog [1,2]. Gases like CF4 are advantageous because they contain flourine which is predicted to have heightened elastic scattering rates with a possible Weakly Interacting Massive Particle (WIMP) DM candidate [3,4,5]. The low pressure of CF4 must be maintained, ideally lower than 100 Torr, in order to elongate potential Nuclear Recoil (NR) tracks which allows for improved directional sensitivity and NR/Electron Recoil (ER) discrimination [6]. Recent evidence suggests that He can be added to heavier gases, like CF4, without significantly affecting the length of 12C and 19F recoils due to its lower mass. Such addition of He has the advantage of improving sensitivity to lower mass WIMPs [1]. Simulations can not reliably predict operational stability in these low pressure gas mixtures and thus must be demonstrated experimentally. In this paper we investigate how the addition of He to low pressure CF4 affects the gas gain and energy resolution achieved with a single Thick Gaseous Electron Multiplier (ThGEM).

Gas gains over 104 and optimisation using 55Fe X-rays in low pressure SF6 with a novel Multi-Mesh ThGEM for directional dark matter searches

The Negative Ion Drift (NID) gas SF6 has favourable properties for track reconstruction in directional Dark Matter (DM) searches utilising low pressure gaseous Time Projection Chambers (TPCs). However, the electronegative nature of the gas means that it is more difficult to achieve significant gas gains with regular Thick Gaseous Electron Multipliers (ThGEMs). Typically, the maximum attainable gas gain in SF6 and other Negative Ion (NI) gas mixtures, previously achieved with an 55Fe X-ray source or electron beam, is on the order of 103 [1,2,3,4]; whereas electron drift gases like CF4 and similar mixtures are readily capable of reaching gas gains on the order of 104 or greater [5,9,7,8,6]. In this paper, a novel two stage Multi-Mesh ThGEM (MMThGEM) structure is presented. The MMThGEM was used to amplify charge liberated by an 55Fe X-ray source in 40 Torr of SF6. By expanding on previously demonstrated results [10], the device was pushed to its sparking limit and stable gas gains up to ˜50000 were observed. The device was further optimised by varying the field strengths of both the collection and transfer regions in isolation. Following this optimisation procedure, the device was able to produce a maximum stable gas gain of ˜90000. These results demonstrate an order of magnitude improvement in gain with the NID gas over previously reported values and ultimately benefits the sensitivity of a NITPC to low energy recoils in the context of a directional DM search.

Cryogenic RPWELL: a novel charge-readout element for dual-phase argon TPCs

The first operation of a cryogenic Resistive Plate WELL (RPWELL) detector in the saturated vapor of liquid argon is reported. The RPWELL detector was composed of a Thick Gas Electron Multiplier (THGEM) electrode coupled to a metallic anode via Fe2O3/YSZ ceramics (Fe2O3 in weight equal to 75%), with tunable bulk resistivity in the range 109–1012 Ω·cm. The detector was operated at liquid argon temperature in saturated argon vapor (90 K, 1.2 bar) and characterized in terms of its effective charge gain and stability against discharges. Maximum stable gain of G≈17 was obtained, without discharges. In addition, preliminary results from novel 3D-printed thermoplastic plates doped with carbon nanotubes are presented.

Electron transfer efficiency in liquid xenon across THGEM holes

Dual-phase liquid-xenon time projection chambers (LXe TPCs) deploying a few tonnes of liquid are presently leading the search for WIMP dark matter. Scaling these detectors to 10-fold larger fiducial masses, while improving their sensitivity to low-mass WIMPs presents difficult challenges in detector design. Several groups are considering a departure from current schemes, towards either single-phase liquid-only TPCs, or dual-phase detectors where the electroluminescence region consists of patterned electrodes. Here, we discuss the possible use of Thick Gaseous Electron Multipliers (THGEMs) coated with a VUV photocathode and immersed in LXe as a building block in such designs. We focus on the transfer efficiencies of ionization electrons and photoelectrons emitted from the photocathode through the electrode holes and show experimentally that efficiencies approaching 100% can be achieved with realistic voltage settings. The observed voltage dependence of the transfer efficiencies is consistent with electron transport simulations once diffusion and charging-up effects are included.

First Observation of Neutral Bremsstrahlung Electroluminescence in Liquid Argon.

A recent discovery of additional mechanism of electroluminescence (EL) in noble gases due to the neutral bremsstrahlung (NBrS) effect led to a prediction that NBrS EL should be present in noble liquids as well. A theoretical model of NBrS EL in noble liquids was developed accordingly in the frameworks of Cohen-Lekner and Atrazhev. In this work, we confirm this prediction: For the first time, visible-range EL has been observed in liquid argon at electric fields reaching 90 kV/cm, using gas electron multiplier (GEM) and thick GEM structures. Absolute light yields of the EL were measured and found to be in excellent agreement with the theory, provided that the momentum-transfer cross section of electron scattering is used for calculation of the NBrS cross section (instead of the energy-transfer one).

The cryogenic RWELL: a stable charge multiplier for dual-phase liquid argon detectors

The operation of a cryogenic Resistive WELL (RWELL) in liquid argon vapor is reported for the first time. It comprises a Thick Gas Electron Multiplier (THGEM) structure coupled to a resistive Diamond-Like Carbon (DLC) anode deposited on an insulating substrate. The multiplier was operated at cryogenic temperature (90 K, 1.2 bar) in saturated argon vapor and characterized in terms of charge gain and electrical stability. A comparative study with standard, non-resistive THGEM (a.k.a LEM) and WELL multipliers confirmed the RWELL advantages in terms of discharge quenching – i.e. superior gain and stability.

Electronic gain study of single resistive electrode thick electron multiplier (RETGEM) radiation detectors with various resistive layers and substrates in P-10 gas

The study of resistive electrode thick gas electron multipliers (RETGEMs) of various designs is described. Four types of RETGEMs were tested. One was made of a substrate of a flame-retardant glass epoxy FR4 board coated with graphite as a resistive layer. The second was made of an FR4 board laminated with Kapton as a resistive layer. The third was made of a polyvinyl chloride (PVC) board coated with graphite as a resistive layer. Finally, a RETGEM with a diamond-like carbon coating produced by CERN was also tested. Multiple characteristics of the single RETGEM detector, such as absolute gas gains and maximum applicable voltages, were measured for all four types of RETGEMs at various voltages applied to the RETGEMs and various sizes of induction gaps, using Cm-244 alpha and F-55 X-ray sources. The results have shown that the highest absolute gas gain is achieved with the FR4 board laminated with Kapton. On the other hand, the PVC board coated with graphite gives the minimum voltage at which the signal can still be observed.

A comprehensive Monte Carlo simulation of the neutron response of multi-element microdosimetric detectors based on THick Gas Electron Multiplier.

We present comprehensive Monte Carlo simulations for the neutron response of the multi-element microdosimetric detector based on THick Gas Electron Multiplier (THGEM). Simulations were carried out using the MCNP6.2 code to calculate the deposited energy spectrum in the gaseous sensitive volumes for three different configurations, 7 × 3, 19 × 5, 37 × 7 that occupy a cylindrical volume of 5-cm diameter by 5-cm length. The energy response was computed from 10keV to 2MeV. The response variation was investigated between sensitive volumes as well as between layers. The simulated energy response showed a good agreement against the evaluated fluence-to-kerma conversion coefficients in the energy region 10-100keV, whereas discrepancies were observed in the region above 250keV. The angular response simulations showed a variation of less than 10%.

Secondary scintillation properties of multi-layer THGEMs operated in low-pressure CF4 and Ar/5%Xe

We present a measurement of the secondary scintillation yield produced by two-layer Thick Gas Electron Multipliers (M-THGEMs) in pure Tetrafluoromethane (CF4) gas and in Ar mixed with 5% Xe in low-pressures down to 20 Torr. The detector was irradiated with 5.49 MeV alpha particles from a low-rate 241-Am source. The secondary scintillation light generated during the gas avalanche process was read out by a Hamamatsu photomultiplier tube (model R8520-406), sensitive to a broad wavelength range (160–650 nm). The avalanche charge was collected on the bottom electrode of M-THGEM and correlated to the scintillation light on an event-by-event basis. We observed that, for both gas types, the value of the photon to electron production ratio (0.4 ph/el in CF4 and 0.1 ph/el in Ar/5%Xe) increases with the thickness of the M-THGEM electrodes and varies significantly with the pressure, being higher at lower values. The decrease in electroluminescence yield at higher pressures is much more pronounced in the Ar/Xe mixture. In addition, because of a larger gas avalanche volume, the electroluminescence light yield is larger in thicker M-THGEM structures. Presented results are particularly useful for designing the next generation of Optical-readout Time Projection Chambers (O-TPCs) operated at low-pressure CF4; applications include experimental nuclear physics with rare isotope beams, dark matter detection with directional sensitivity and observation of the Migdal effect in a low-pressure Optical TPC.

Directional dark matter readout with a novel multi-mesh ThGEM for SF6 negative ion operation

Abstract Direct searches for Weakly Interacting Massive Particle (WIMP) dark matter could greatly benefit from directional measurement of the expected induced nuclear recoils. Gas-based Time Projection Chambers (TPCs) offer potential for this, opening the possibility of measuring WIMP signals below the so-called neutrino floor but also of directional measurement of recoils induced by neutrinos from the Sun, for instance as proposed by the CYGNUS collaboration. Presented here for the first time are results from a Multi-Mesh Thick Gas Electron Multiplier (MM-ThGEM) using negative ion gases for operation with such a directional dark matter TPC. Negative ion drift gases are favoured for directionality due to their low diffusion characteristics. The multiple internal mesh structure is designed to provide a high gain amplification stage when coupled to future large area Micromegas, strip or pixel charge readout planes. Experimental results and simulations are presented of MM-ThGEM gain and functionality using low pressure pure CF4, SF6 and SF6:CF4 mixtures irradiated with alpha particles and 55Fe x-rays. The concept is found to work well, providing stable operation with gains over 103 in pure SF6.

Performance of prototype dual gain multilayer thick gas electron multiplier with high-intensity heavy-ion beam injections in low-pressure hydrogen gas

Abstract A prototype Dual Gain Multilayer Thick Gas Electron Multiplier (DG-M-THGEM) with an active area of 10 cm × 10 cm was manufactured aiming at the production of a large-volume active-target time projection chamber which can work under the condition of high-intensity heavy-ion beam injections. The DG-M-THGEM has an alternating structure of electrodes and insulators. Effective gas gains of two regions, which are called beam and recoil regions, are separately controlled. Performance of the prototype DG-M-THGEM in hydrogen gas at a pressure of 40 kPa was evaluated. Irradiating a 132Xe beam, an effective gas gain lower than 100 with a charge resolution of 3% was achieved in the beam region while an effective gas gain of 2000 was maintained in the recoil region. Position distributions of measured charges along the beam axis were investigated in order to evaluate gain uniformity in the high-intensity beam injection. The gain shift was estimated by simulations considering space charges in the drift region. The gain shift was suppressed within 3% even at the beam intensity of 2.5 × 106 particles per second.

Design and studies of thick Gas Electron Multipliers fabricated in India

THick Gas Electron Multipliers (THGEMs) are robust and high gain Micro Pattern Gaseous Detectors which are economically manufactured by standard drilling and etching of thin printed circuit boards. In this paper, we present our recent simulation as well as experimental studies on THGEMs which have been fabricated in India using local expertise. Two types of THGEMs have been fabricated; one set has holes without any external rim and another set has holes with rims. These detectors have been characterized using argon-carbon dioxide and argon-isobutane gas mixtures. Electron transmission, effective gain, energy resolution, optimized working range and charging up studies have been presented for both the sets of THGEMs.

Design of a Thick Gas Electron Multiplier based photon pre-amplifier

In this paper we present the design of a photon pre-amplifier based on a photo-cathode coated Thick Gas Electron Multiplier (THGEM). Such device is crucial in application where a weak light signal produced in a radiation detector must be amplified so that it can be carried to a photo-detector by means of optical fibres. An example of a device where a light signal must be amplified is a gamma-ray Cherenkov detector for fusion power measurements in magnetic confinement devices. In such application the active part of the detector must be located very close the plasma, typically in a harsh radiation environment where standard photodetectors cannot operate. The photon pre-amplifier allows to increase the signal generated in the active part of the detector so that it can be easily detected by the photodetector located outside the harsh environment. We present the conceptual design of a THGEM based photon pre-amplifier supported by Garfield++ simulations. The device working principle is the following: primary photons impinge on the photo-cathode and extract electrons that are accelerated by the THGEM electric field. Upon collisions with the accelerated electrons, the gas molecules in the pre-amplifier are brought to excited states and de-excite emitting scintillation photons. Since each electron excites multiple gas molecules, the scintillation photons outnumber the primary photons, leading to the amplification. In addition, we present the first observation of measurements of Nitrogen gas scintillation in a THGEM device. We devised an experimental setup consisting of a vacuum chamber containing a THGEM and an alpha particle source. The vacuum chamber is filled with pure nitrogen and is coupled to a photomultiplier tube via a view-port to detect the scintillation photons generated in the THGEM. For sake of simplicity the electrons that induce the scintillation are generated by the ionization track of an alpha particle rather than by the THGEM photo-cathode coating. A good qualitative agreement between simulations and experiment has been found, however no quantitative conclusions can be made due to the lack of N2 excitation cross sections in the Garfield++ code.

First results on FHM — a Floating Hole Multiplier

A proof of principle of a novel concept for event recording in dual-phase liquid xenon detectors — the Floating Hole Multiplier (FHM) — is presented. It is shown that a standard Thick Gaseous Electron Multiplier (THGEM), freely floating on the liquid xenon surface permits extraction of electrons from the liquid to the gas. Secondary scintillation induced by the extracted electrons in the THGEM holes as well as in the uniform field above it was observed. The first results with the FHM indicate that the concept of floating electrodes may offer new prospects for large-scale dual-phase detectors, for dark matter searches in particular.

Construction and test of a transition-radiation detector prototype based on thick gas electron multiplier technology

A transition-radiation detector (TRD) is a powerful device for highly relativistic electron (γ ≳ 1,000) identification. Electron identification is crucial for tagging the outgoing scattered electrons in an electron-ion collider (EIC) detector. Employing a TRD at the electron forward region of an EIC detector can provide the necessary electron identification with high hadron rejection over a wide momentum range. Thick gas electron multiplier (THGEM) technology is suitable for radiation detection in modern high-energy experiments owing to its high-granularity structure, radiation hardness, high-rate capability and ease of large-area production. This study investigates a TRD prototype based on THGEM technology through soft X-ray and electron beam experiments. Geant4 simulation were extensively exploited to understand the operation of TRD prototype with different gas mixtures. Particularly, the performance of TRD prototype with an electron beam at the DESY, with argon-based gas rather than xenon-based gas, agreed well with the simulation analyses in all important aspects. Based on the consistency of the experimental and simulation results, a likelihood analysis on the simulated total energy deposit in the xenon-based working gas would suggest a pion rejection improvement with the optimization of detector design, readout electronics and identification algorithm.

Study on the wide range gamma dose rate response for a new type thick gas electron multiplier

Study on the wide range gamma dose rate response for a new type thick gas electron multiplier

Systematic investigation of critical charge limits in Thick GEMs

We present discharge probability studies performed with a single Thick Gas Electron Multiplier (THGEM) irradiated with alpha particles in Ar-CO2 and Ne-CO2 mixtures. We observe a clear dependency of the discharge stability on the noble gas and quencher content pointing to lighter gases being more stable against the development of streamer discharges. A detailed comparison of the measurements with Geant4 simulations allowed us to extract the critical charge value leading to the formation of a spark in a THGEM hole, which is found to be within the range of (3 to 7)×106 electrons, depending on the gas mixture.Our experimental findings are compared to previous GEM results. We show that the discharge probability of THGEMs exceeds the one measured with GEMs by orders of magnitude. This can be explained with simple geometrical considerations, where primary ionization is collected by a lower number of holes available in a THGEM structure, reaching higher primary charge densities and thus increasing the probability of a spark occurrence. However, we show that the critical charge limits are similar for both amplification structures.

Development of THGEM-based Detectors for Nuclear Fission Studies

To optimize the exploration of Super Heavy Elements (SHE), the key challenge is to understand the dynamics of the fusion-fission through the measurements of mass and angular distribution of the fission fragments. For the detection of fission fragments, position sensitive Multi-Wire Proportional Counters are generally used due to their high gain, good temporal and position resolution. However, these detectors use fragile anode wires having a diameter of only 10 μm and therefore they are vulnerable. In the present work, a detector based on robust Thick Gaseous Electron Multiplier (THGEM) has been proposed. A numerical demonstration of THGEM-Multi Wire hybrid detector technology as a possible candidate for the new generation low-energy fission studies and their evaluation as a function of different possible geometric and electric configuration in low-pressure gas is discussed here.

Charging up studies in thick Gas Electron Multipliers

Gaseous ionization detectors that have insulating media exposed to the active gas volume have issues related to charging up of the insulators during the course of its use[1]. The time-dependent variation of detector response in hole-based Micro-Pattern Gaseous Detectors (MPGDs), especially THick Gas Electron Multipliers (THGEMs), is one of the challenging problems that has been attributed to “charging up” and “charging down”. Experimental studies of stabilization of THGEM gas gain with time in argon-based mixtures under various experimental conditions will be presented here. Effects of different sources with varying irradiation rates on the gain saturation process have been studied. It has been observed that low-rate source shows two-step gain stabilization phenomena, one short-term saturated gain, another long-term saturated gain, whereas high-rate source shows just one-step gain saturation. While this two-step stabilization has been attributed to the charging up of the rim by earlier studies, its effect seems to be subdued for high-rate irradiation according to the present studies. The results provide an insight into the dynamics of gain saturation in THGEMs.