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For experiments on very thin and flat liquid water targets, we propose the use of colliding water-jets (Savart 1833, G.I. Taylor 1959, and S.P. Lin 2003). Here, two circular jets interpenetrate at several millimeters distance from the nozzles and form a flat, lancet-shaped, liquid sheet, up to 1 mm wide and with very low thickness. Analogous to the single liquid-jet decay laws (worked out by G.I. Taylor, by Lord Rayleigh, and many recent authors) these leaf-like flat surface structures decay, already, after a few 100 μm propagation. But, it has the benefits of being located in free space in more than 1 mm distance from the nozzle exit planes. And, in addition the liquid sheet surfaces are very smooth, as is visible in the photographs shown in upper figure.


Figure description: Liquid sheet flat target, produced by the collision of two circular water jets. The circular jets have 10 μm diameter, running at liquid volume flow of 0.36 ml min-1in these feasibility tests in atmospheric air (Microliquids GmbH, March 2011). The collision formed, flat, lancet-shaped or bell-shaped liquid sheet has an extension of 0.25 mm to 0.5 mm, at a sheet thickness in the 1 μm range. Shown are screen shots from a video record of the tests. (for a reference.length scale: The outer diameter of the nozzle tips is 1 mm.)

The long-term stability of the collision generated liquid sheet is under active study and development by Microliquids. It will require, possibly, vibration damping mechanical structures. A drift compensation mechanism comprising nano-actuators and video- control for jet stabilisation is running in a first test-phase. The pumping problems in high vacuum will be more formidable, due to the spraying decay of a liquid sheet, and will have to be solved in a more complicated way than in the single circular jet case. First tests indicate 10-3 mbar may be achieved in a standard test vacuum chamber with additional liq. N2
cryotraps.