Electroluminescence and Electron Avalanching in Two-Phase Detectors

Abstract

Electroluminescence and electron avalanching are the physical effects used in two-phase argon and xenon detectors for dark matter searches and neutrino detection, to amplify the primary ionization signal directly in cryogenic noble-gas media. We review the concepts of such light and charge signal amplification, including a combination thereof, both in the gas and in the liquid phase. Puzzling aspects of the physics of electroluminescence and electron avalanching in two-phase detectors are explained, and detection techniques based on these effects are described.

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

“…In argon, ordinary electroluminescence (in the VUV, around 128 nm, see Fig. 1) goes via Ar * (3p 5 4s 1 ) atomic excited states [7] and thus has a threshold for the reduced electric field of about 4 Td [15], which is defined by the energy threshold for Ar atom excitation. The reduced electric field is defined as E/N expressed in Td units (1 Td = 10 −17 V cm 2 ) corresponding to 0.87 kV/cm in gaseous argon at a pressure of 1.00 atm and a temperature of 87.3 K, where E is the electric field and N is the atomic density.…”

“…At higher electric fields (above 8 Td), another "nonstandard" EL mechanism comes into force, namely that of electroluminescence in the NIR due to transitions between excited atomic states [7,14,[17][18][19][20]: Ar * (3p 5 4p 1 ) −→ Ar * (3p 5 4s 1 ). It has a line emission spectrum in the range of 700-850 nm (Fig.…”

“…S2 detection in dual-phase detectors relies on proportional electroluminescence (EL) in the noble gas [6,7]. In argon, the ordinary ("standard") mechanism of proportional electroluminescence is considered to be due to vacuum ultraviolet (VUV) emission (around 128 nm) of noble gas excimers Ar * 2 ( 1,3 + u ) produced in three-body atomic collisions of excited atoms Ar * (3p 5 4s 1 ), which in turn are produced by drifting electrons in electron-atom collisions: see review [7].…”

“…In this case, the detection threshold for the S2 signal can be significantly decreased, compared to direct SiPM-matrix readout. It should be remarked that the concept of THGEM/SiPMmatrix readout overlaps with the earlier idea of Cryogenic Avalanche Detectors (CRADs), developed elsewhere [7,26,27]. In CRADs, the charge multiplication or avalanche scintillation signal from the THGEM (or GEM), placed in the gas phase of the two-phase detector, is recorded.…”

Optical Readout of the ARIADNE LArTPC Using a Timepix3-Based Camera

“…However, the THGEM amplification process also produces secondary scintillation light -typically hundreds of photons per electron [12][13][14]. This light can then be easily detected by modern optical imaging devices, which can be sensitive at the single-photon level.…”