Numerisch-theoretisch und experimentelle Untersuchung einer Hochstrom-Fernfokus-Elektronenkanone vom Tetroden-Typus

Starting from a earlier investigation of a telefocus-electron gun of the triode-type (Z. angew. Phys.11, 370 (1950) which however was unable to deliver high beam currents, a telefocus-gun of the tetrode-type for high beam currents was theoretically and experimentally investigated and the main results are presented in this paper. In the first part of this work a model-system has been investigated by numerical-theoretical methods to get an idea of the electron paths inside the gun as well as to estimate the highest obtainable perveance of the gun. In these investigations an analogy-resistance-network for the plotting of potential fields and an electronic computer for the electron path calculations have been used. These calculations showed that an electron-gun of small geometrical dimensions can be built which is able to focus high beam currents at long distances from the cathode. The relevant gung parameters are a short distance from cathode to first-anode and a high negative Wehnelt-potential. In the second part of the paper the results of some experimental investigations are reported. The experiments showed that by suitable dimensioning a 50 mA, 20 kV electron beam can be focussed in a crossover of some few tenths of mm diameter at a distance of 150–250 mm from the cathode. Some examples for the gun data are given. The aberrations of the electron gun are considerable at the higher currents: At 20 kV one can easily obtain a beam current of 150 mA with a cathode of 2 mm diameter. The aberrations influence infavourably the current density distribution in the crossover. The disturbance is especially noticeable for long cathode to focus distances as was the case in some reported experiments with a cathode to focus distance of 410 mm.The described telefocus-gun has been used for electron beam welding and some practical conclusions of these experiments are discussed in the paper.

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Leicht gekürzte Fassung eines Vortrages an der Second International Conference on Electron and Ion Beam Science and Technology, New York, April 17–20, 1966.