Experimental thermionic energy converter without enclosure: A molecular beam supplied converter

Experimental thermionic energy converters of an open type, i.e. with no closely located surrounding walls, as proposed here, have many advantages compared to conventional enclosed converters. Interactions with and problems of the enclosure do not interfere with the fundamental plasma and surface processes, which can be studied efficiently in an open converter, for example by mass spectrometry, optical spectroscopy, electron energy analysis and surface analytical methods. An open converter has been built and tested, where the necessary alkali vapour is supplied by a molecular beam type source with 400 laser bored effusion holes. The source acts as collector in front of a directly heated emitter. An ignited mode behaviour can be reached easily. The examples of results presented for Mo and Pt emitters at 1600–1700 K, a Cs plasma and nickel collector give a power density of 1–2 W cm^–2 and a minimum barrier index of 1.95–2.1 eV and indicate a behaviour similar to enclosed converters. Thus, results for new surfaces, new additives etc. found in open converters should be of direct relevance for the development of normal enclosed converters.