Abstract
In bubble-assisted Liquid Hole Multipliers (LHM), developed for noble-liquid radiation detectors, the stability of the bubble and the electro-mechanical properties of the liquid-to-gas interface play a dominant role in the detector performance. A model is proposed to evaluate the static equilibrium configurations of a bubble sustained underneath a perforated electrode immersed in a liquid.For the first time bubbles were optically observed in LAr; their properties were studied in contact with different material surfaces. This permitted investigating the bubble-electrodynamics via numerical simulations; it was shown that the electric field acts as an additional pressure term on the bubble meniscus.The predictions for the liquid-to-gas interface were successfully validated using X-ray micro-CT in water and in silicone oil at STP. The proposed model and the results of this study are an important milestone towards understanding and optimizing the parameters of LHM-based noble-liquid detectors.
Highlights
While their existence is granted, their location is entirely dependent on the details of the edge smoothing
The electric force (2.1) on the interface between gas and liquid was implemented, in COMSOL parlancy, as a weak contribution on the fluid-fluid boundary, using test functions. The focus of this investigation is the effect of the electric field on the meniscus position, and the schematic boundary conditions imposed on the reduced domain may be somewhat inadequate for a real detector with a 3D structure
Repeating the procedure for different values of the control parameters it was possible to discriminate intervals of existence of the equilibrium, like shown in Fig. 15 for varying H and V0
Summary
We examine the properties of a gas bubble formed and sustained under a THGEM-electrode. The force Fs acting on the surface element of the gas-to-liquid interface is described as the Young-Laplace pressure pL pLn. where γ is the surface tension between the two phases and r the local radius of curvature of the meniscus. The meniscus settles on a position which, to the prescribed θ, presents a downward concavity with the radius of curvature balancing the bubble pressure, and realizes a stable equilibrium with respect to movements normal to the interface center. The electric field E applied across the hole (see Fig.2) adds the term (2.1) to Eq(2.3) and (2.4), transforming them into p1 It requires a different value of the radius of curvature r in order to satisfy Eq.2.6.
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