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a b s t r a c tWe have built a RICH detector prototype consisting of a liquid C 6 F 14 radiator and six triple Thick Gaseous Electron Multipliers (TGEMs), each of them having an active area of 10 Â 10 cm 2 . One triple TGEM has been placed behind the liquid radiator in order to detect the beam particles, whereas the other five have been positioned around the central one at a distance to collect the Cherenkov photons.The upstream electrode of each of the TGEM stacks has been coated with a 0.4 mm thick CsI layer.In this paper, we will present the results from a series of laboratory tests performed with this prototype carried out using UV light, 6 keV photons from 55 Fe and electrons from 90 Sr as well as recent results of tests with a beam of charged pions where for the first time Cherenkov Ring images have been successfully recorded with TGEM photodetectors. The achieved results prove the feasibility of building Cherenkov detector based on CsI coated TGEMs.

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We study here experimentally, numerically and using a lubrication approach; the shape, velocity and lubrication film thickness distribution of a droplet rising in a vertical Hele-Shaw cell. The droplet is surrounded by a stationary immiscible fluid and moves purely due to buoyancy. A low density difference between the two mediums helps to operate in a regime with capillary number Ca lying between 0.03 − 0.35, where Ca = µ o U d /γ is built with the surrounding oil viscosity µ o , the droplet velocity U d and surface tension γ. The experimental data shows that in this regime the droplet velocity is not influenced by the thickness of the thin lubricating film and the dynamic meniscus. For iso-viscous cases, experimental and three-dimensional numerical results of the film thickness distribution agree well with each other. The mean film thickness is well captured by the Aussillous & Quéré (2000) model with fitting parameters. The droplet also exhibits the "catamaran" shape that has been identified experimentally for a pressure-driven counterpart (Huerre et al. 2015). This pattern has been rationalized using a two-dimensional lubrication equation. In particular, we show that this peculiar film thickness distribution is intrinsically related to the anisotropy of the fluxes induced by the droplet's motion.

It was recently demonstrated that feeding a silicon-in-silica coaxial fibre into a flame-imparting a steep silica viscosity gradient-results in the formation of silicon spheres whose size is controlled by the feed speed [Gumennik et al., Nat. Commun. 4, 2216(2013]. A reduced model to predict the droplet size from the feed speed was then derived by Mowlavi et al. [Phys. Rev. Fluids. 4, 064003 (2019)], but large experimental uncertainties in the parameter values and temperature profile made quantitative validation of the model impossible. Here, we validate the reduced model against fully-resolved three-dimensional axisymmetric Stokes simulations using the exact same physical parameters and temperature profile. We obtain excellent quantitative agreement for a wide range of experimentally relevant feed speeds. Surprisingly, we also observe that the local capillary number at the breakup location remains almost constant across all feed speeds. Owing to its low computational cost, the reduced model is therefore a useful tool for designing future experiments.