The wisdom of a centenary [oxide cathode]

This year we celebrate the centennial of the invention of the oxide cathode. In 1904 A. Wehnelt described in an epoch-making paper the positive effect of alkaline earth oxide coatings on the electron emission of hot metals. The title of Wehnelt\´s German paper was "Uber den Austritt negativer Ionen aus gluhenden Metallverbindungen und damit zusammenhangende Erscheinungen". In English this means "On the emission of negative ions from glowing metal compounds and corresponding phenomena". This paper was the start of the unequalled success of the oxide cathode, since it enabled the development of electron valves in the first half of the 20th century. So, the oxide cathode was the basic device and the enabler of the electronic industry before the introduction of solid-state transistors. In this tribute to the centenary oxide cathode the author focuses on the evolution of the grand ideas and theories regarding the mechanism and endurance of its electron emission. Usually these two aspects of the oxide cathode are considered as separate categories, however in this conference, uniting these concepts will be tried. Product-oriented topics such as heater-cathode insulation and the influence of residual gases on the electron emission will be excluded in this tribute.