Investigations of Electra KrF laser hibachi foil cooling with small obliquely impinging jets

Electra is a large electron beam pumped KrF laser with transmission foils that separate the vacuum diodes from the laser gas. Active cooling of these foils is important when Electra operates at a rep-rate of 5 Hz because the attenuation of the electron beam by the foil produces a volumetric heating source. A method adopting a large number of locally injected high-speed circular gas jets was explored experimentally and numerically for the purpose of cooling and protecting the hibachi foil with an enhanced convection heat transfer rate. The jets were issued from the openings on two stainless-steel jet tubes parallel to the foil in a fashion such that the two straight lines of jets impinge on the foil obliquely and form a staggered coverage of the foil. CFD simulations were performed to identify the best jet impingement configuration. Bench-top experiments were performed at various jet diameters and jet velocities for a single foil span between two neighboring supporting ribs with a surface heat flux over 20.0 kW/m(2). Heat transfer enhancement of 60-700% over the case with jets turned off was observed depending on jet Reynolds numbers. Experimental Nusselt numbers were well-correlated with jet Reynolds number and the normalized jet-to-foil distance. The study shows, that the impinging jets enhance heat transfer from the surface and offer an improved average cooling for a much larger foil area. (C) 2012 Elsevier B.V. All rights. reserved.