Modes of Operation of an Electron Beam Floating Zone Melting Furnace: Growth of Single Crystals of Metals and Alloys

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Abstract
An electron beam melting furnace constitutes a dynamic high vacuum diode which has theoretically six modes of power regulation as a consequence of the current‐voltage characteristic of the furnace and the choice between constant‐current or constant‐voltage control. Among the six possible modes, three are unstable and three are useful. Preference is given to constant‐current control as this is more efficient than constant‐voltage control and has the added advantage of an electrothermal feedback loop which increases the stability of regulation. A single tube constant‐current regulator is described which utilizes tungsten filament lamps in the feedback loop. This regulator was incorporated in the power system of an electron beam melting furance. Numerous single crystals of tungsten, other metals, and alloys were grown. The performance of the furnace and the quality of the crystals are discussed.

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