Electron beam deflecting magnet assembly for a scanning electron beam computed tomography scanner

A magnet coil assembly is described for controllably deflecting an incident electron beam in an electron beam system such as a computed tomography scanner. It comprises a pair of x- and y-coils and a generally cylindrical support form supporting the x-coil and the y-coil at physically different radii a/sub x/ and a/sub y/, the coils being at angular positions π/2 relative to one another and defining a generally cylindrical configuration about the axis. An angle phi defines the plane of deflection relative to a fixed plane containing the magnetic coil axis and polar coordinates (r,θ) define the location in a plane defined by mutually orthogonal coordinate axes (x,y) normal to the magnetic coil axis; each coil comprising a selected number of continuous turns comprising a pair of generally axially-extending sections joined by end connecting sections; the direction and configuration of the coils being selected such that for currents I/sub x/ proportional to - sin phi and I/sub y/ proportional to cos phi producing magnetic fields B/sub x/ equal to - B/sub x/ sin phi and B/sub y/ equal to B/sub o/ cos phi then, to a selected accuracy, the magnitude of the resultant magnetic field approximates B/sub o/=(B/sub x//sup 2/+B/sub y//sup 2/)/sup 1/2/, which is a constant independent of R, θ and phi, and the field direction B/sub x//B/sub y/ approximates B/sub x//B/sub y/=-tan phi, independent of r and θ