The possibility of applying the phenomena of superconductivity to electron optical lenses was probably first proposed by Boersch in 1934 at the Berlin Laue colloquium, after the presentation of Meissner’s paper on field repulsion in superconductors. Because the superconductors known at that time exhibited relatively low critical temperatures and small critical current densities at high fields, the problem was not further pursued. After the discovery of the high-temperature superconductors NbN and NbC [a transition temperature above 20 K was published for these compounds as the result of a measurement error (Aschermann et al., 1941)], Diepold and Dosse (1941) invented a superconducting lens. The patent specification describes a device in which the imaging effect is produced by a superconducting ring enclosed in a helium container. The excitation of the ring is produced by a normal-conducting iron circuit magnet inside the microscope. Also described is a magnetization device outside the microscope for exciting the ring. The cooled part of the apparatus, the magnetized superconducting ring in its helium container, has to be introduced into the microscope. A shim coil is added for focusing. Judging this invention with the knowledge acquired in the last 35 years, we see immediately that it could never work. However, it is interesting to note that many of the remarkable features of superconducting lenses had already been described at that time.
KeywordsHistorical Survey Imaging Effect Magnetization Device Patent Specification Exceptional Stability
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