New types of crossed field electron guns

A new analytical method of designing M-type crossed field electron guns will be described. These guns are based upon an exact space charge flow solution obtained a number of years ago by Pembank, Brillouin and others. The actual design procedure is essentially the same as for "Pierce Guns," and the precise electrode shapes are obtained by a method of conformal mapping and a subsequent numerical calculation. Two types of guns result from this procedure. The first, somewhat similar to the French "short gun", has been constructed and extensively studied. This gun is characterized by an almost complete absence of sole current. Approximate expressions relating current, voltage and magnetic field have been derived for this gun and experimental values are within a few percent of these calculations. Visual observations indicate the shape of the beam in the gun to be essentially as predicted by theory. A convergence of approximately 7:1 has been obtained with this gun. A second type of gun, based on an approximation to the exact flow solution is possible. This gun is characterized by an extremely high convergence and operates at a somewhat higher magnetic field than the short gun. A gun of this type has been constructed and appears to give a fairly well defined beam with approximately the predicted current.