GB1135290A - Improvements in or relating to electron beam apparatus - Google Patents

Abstract

1,135,290. Electron beam furnaces. AIR REDUCTION CO. Inc. 25 May, 1966 [18 June, 1965], No. 23277/66. Heading H1D. In an electron beam furnace the beam from an electron source 13 situated below the crucible 47, Fig. 1, or to one side below a lateral shelf 29, Fig. 7, is passed through a focusing and deflecting magnetic field which first increases in strength and is then constant either over the remaining portion of the path or over an intermediate region which is followed by a region in which the field decreases in strength or is of constant strength but lower magnitude. The flux lines of the field of increasing in strength increase in curvature in the direction of the electron source. As shown in Fig. 1, the magnetic system comprises two pairs of polepieces 23, 23a and 63, 63a, energizing coils 51, 53, 55 and a ferromagnetic base plate 49. The source 13 is situated in the fringe field of polepieces 23, 23a and the field increases to a region of constant intensity between parts 70, 70a of the polepieces 23, 23a. A weaker but constant field is provided between polepieces 63, 63a. In Fig. 7 the polepieces 77 shaped as shown are spaced from the side limbs of a U-shaped ferromagnetic support 89 by a plurality of coils shown in dotted lines. The ampere-turns of these coils may be individually varied. In another embodiment with a rotating crucible 101, Fig. 8, in which due to centrifugal force the molten material is urged into a slot in the inside wall of the crucible, a plurality of electron sources 13 are provided, each source being associated with an electromagnet comprising angularly disposed polepieces 109, 109a and parallel pole faces at the ends of the polepieces. In a further embodiment, Fig. 11 (not shown), the beam passes between parallel polepieces of a U-shaped electromagnet. Guidance is given in the Specification as to the extents of the various magnetic field regions along the beam path.