SHUNT FOR MAGNETIC SYSTEMS USING PERMANENT MAGNETS

摘要

1292073 Permanent magnets; transit-time tubes J A MELNIKOV 2 April 1970 15649/70 Headings H1D and H1P In a permanent magnet, e.g. for a magnetron or travelling wave-tube or for a magnetic focusing system, poles 1 co-operating with shielding yoke 3 are surrounded by annular discs 2 of magnetically soft material variably separated by ring 4 of high thermal expansivity, which shunt the magnet field so that variations of gap magnetic flux with temperature are compensated (Figs. 1a, 1b). The discs may have orthogonal projecting lugs sliding one over the other to provide a shunting flux path (Figs. 2a, 2b, not shown). A ring magnet 6 having end polepieces 7 (Figs. 3, 4) may be surrounded by annular magnetically soft discs 2 having studs 8 engaging inclined grooves of a split ring 9 of high thermal expansivity anchored at one end to the polepieces, so that the disc separation is varied with temperature to compensate flux variations. Two radially magnetized rings co-operating with a yoke (Figs. 5, 6, not shown) may have opposed hollow central polepieces containing elements of high thermal expansivity adjusting the spacing of conical spring steel discs from the magnetic rings, to compensate variations of gap flux. A focusing magnet (Figs. 7, 8) comprises an inner tube surrounded by ring magnets 6 and surrounding magnetically soft spaced discs 2, interconnected by a magnetically soft bar 16 terminating in an end member attached to a compensating pair of diametrically opposed bars 17 of high thermal expansivity; which expand and contract with temperature change, shifting the discs towards and away from the centres of the magnet rings, whereby changes of magnetic flux in the inner tube is compensated for temperature change. In a modification (Figs. 9, 10, not shown) magnetically soft rings surround each magnet circumferentially and fully or partly overlie adjacent polepieces whereby a portion of the flux is shunted. Diametrically opposed bars of highly thermal expansive material are arranged to traverse the rings with temperature changes over the magnets and polepieces to compensate the flux in the inner tube. The magnets may be ferrite.