Electron emission properties of two-phase argon and argon-nitrogen avalanche detectors

Abstract

Electron emission properties of two-phase Ar avalanche detectors are studied. The detectors investigated comprised a liquid Ar or Ar+N 2 layer followed by a multi-GEM multiplier operated in the saturated vapour at 84 K. Two components of the electron emission through the liquid-gas interface were observed: fast and slow. In Ar, the slow emission component dominated even at higher fields, reaching 2 kV/cm. In Ar+N 2 on the contrary, the fast emission component dominated at higher fields, the slow component being disappeared. This is explained by the electron backscattering effect in the gas phase. The slow component decay time constant was inversely proportional to the electric field, which is compatible with thermionic emission model. The electron emission efficiencies in two-phase Ar and Ar+N 2 were estimated to be close to each other.

Revealing neutral bremsstrahlung in two-phase argon electroluminescence

“…At lower electric fields, q e was determined by extrapolation using the field dependence of the X-ray ionization yield in liquid Ar [36]. At that, the electron transmission through the THGEM0 electrode, determined by us using 3D simulation, and the emission efficiency through the liquid-gas interface, studied elsewhere [56], were taken constant in a given field range.…”

First demonstration of a bubble-assisted Liquid Hole Multiplier operation in liquid argon

“…First, Ar has two decay constants for the scintillation or EL signal, 5 ns and 860 ns, as opposed to Xe where the longest timescale is 27 ns [17]. Then, the transition of electrons from liquid to gas has, according to [18], both long and short timescales. None of them, however, can explain the 3-4 µs decay constant, observed with the two different sensors.…”

Two-phase Cryogenic Avalanche Detectors with THGEM and hybrid THGEM/GEM multipliers operated in Ar and Ar+N2

“…The idea of doping liquid Ar with N 2 to improve the performance of either liquid Ar TPCs [31], [32], [33] or two-phase Ar CRADs [12] has appeared repeatedly. In the latter case, an interesting effect appeared: the slow component of the electron emission through the liquid-gas interface almost fully converted to the fast emission one [12]. This would make two-phase Ar+N 2 CRADs substantially faster compared to that with pure Ar.…”

“…This would make two-phase Ar+N 2 CRADs substantially faster compared to that with pure Ar. Indeed, in two-phase Ar CRADs, at typical operating fields of ~2 kV/cm in the liquid, the slow component has a time constant of ~5 µs and amounts to ~60% of the total signal [12], which makes them relatively slow. Note that the observations of the slow component were made possible through the use of fast GEM multipliers [12] or that of THGEM with GAPD-based optical readout [16].…”

“…Another way to increase the CRAD gain limit was proposed in [12]: it was suggested to add a N 2 additive to two-phase Ar. This was based on the observation that the GEM or THGEM maximum gain in mixtures of Ar and N 2 , even with minute N 2 contaminations, can be considerably higher compared to that of pure Ar [13], [14].…”