Internal magnetic lens for electron beams

Claim 1

AN ELECTRON TUBE OF THE CATHODE RAY TYPE IN WHICH A BEAM IS FOCUSED ONTO A SURFACE COMPRISING: (A) A SOURCE OF ELECTRONS, (B) A TARGET DISPLACED THEREFROM FOR RECEIVING THE ELECTRONS EMITTED FROM SAID SOURCE, (C) MEANS FOR PROVIDING AN ELECTRON ACCELERATING ELECTRIC FIELD FOR ACCELERATING THE EMITTED ELECTRONS AWAY FROM SAID SOURCE IN A DIRECTION TOWARDS SAID TARGET, SAID ELECTRIC FIELD HAVING AN INITIAL ACCELERATING PORTION IN THE VICINITY OF THE SAID SOURCE OF A CONFIGURATION SUCH AS TO CAUSE THE ACCELERATED ELECTRONS TO CONVERGE IN A CROSSOVER REGION, (D) A THINK DISK PERMANENT MAGNET HAVING A SMALL APERTURE THEREIN POSITIONED WITHIN SAID TUBE IN THE VICINITY OF SAID SOURCE AT SAID CROSSOVER REGION, SAID DISK MAGNET BEING CONSTRUCTED TO HAVE A RADIUS THAT IS NO GREATER THAN ON THE ORDER OF THREE TIMES THE AXIAL SPACING BETWSEEN SAID MAGNET AND SAID SOURCE FOR GENERATING A TORODIAL MAGNETIC FIELD OF RESTRICTED AXIAL DIMENSION EFFECTIVE IN THE INITIAL ACCELERATING PORTION OF SAID ELECTRIC FIELD, SAID MAGNETIC FIELD HAVING A SUBSTANTIAL RADIAL COMPONENT AT THE EMISSIVE SURFACE OF SAID SOURCE FOR DIRECTING SAID ACCELERATED ELECTRONS THROUGH SAID APERTURE TO PROVIDE A CONSTRICTED CROSSOVER REGION, AND (E) ELECTRON FOCUSING MEANS POSITIONED BETWEEN SAUD DISK AND SAID TARGET FOR IMAGING SAID CONSTRICTED CROSSOVER REGION ON TO SAID TARGET.