THE DEVELOPMENT OF HIGH ELECTRICAL GRADIENT, DC ACCELERATOR TUBES WITH ELECTRICAL BREAK- DOWN PROTECTION

THIS PROJECT IS TO PRODUCE A SHORT SECTION OF A DC PAR- TICLE ACCELERATOR TUBE INCORPORATING SEVERAL IMPROVEMENTS. THE ELECTRODES WILL HAVE A CONTINUOUS CURVATURE OF LARGE RADIUS, SO AS TO PROVIDE ELECTROSTATIC SHIELDING FOR THE SEPARATING INSULATOR WITHOUT PRODUCING THE LARGE, LOCAL ELECTRIC FIELD ENHANCEMENTS TYPICAL OF DISHED ELECTRODES. THE ACCELERATING APERTURE OF THESE ELECTRODES WILL BE CHOSEN SO THAT A FIELD-EMITTED ELECTRON ALWAYS STRIKES THE NEXT ELECTRODE, WHEREAS A FIELD-EMITTED OR ELECTRON- SPUTTERED POSITIVE IRON TRAVELS WITHOUT FURTHER COLLISION INTO AN ION/ELECTRON TRAP PLACED IN A FIELD-FREE REGION AT INTERVALS ALONG THE ACCELERATOR TUBE. HERE, PRIMARY POSITIVE IONS AND SECONDARY PARTICLES, BOTH IONS AND ELECTRONS, WILL BE ELIMINATED. THE INTERGAP INSULATORS ARE DESIGNED USING TWO NOVEL PRINCIPLES: THE ELECTRODE DIRECTION AT THE INSULATOR IS AT AN ANGLE TO THE TUBE AXIS (INSTEAD OF NORMAL AS IN PREVIOUS DESIGNS); AND THE VACUUM SIDE INSULATOR CONTOUR IS CHOSEN SO THAT IONS OR ELECTRONS LEAVING THE INSULATOR SURFACE DO NOT STRIKE THE INSULATOR AGAIN, THUS ELIMINATING THE "ELECTRON MULTIPLIER" EFFECT THAT CAUSES PATCHES OF CHARGE, AN ATTENDANT NONUNIFORM POTENTIAL GRADIENT, TO APPEAR ON CONVENTIONAL INSULATOR SURFACES. EXTERNAL TO THE TUBE, A SERIES OF TRIGGERED SPARK GAPS IS PROVIDED, ARRANGED SO THAT AN ELECTRODE DRAWING EXCESSIVE CURRENT BECAUSE OF INCIPIENT FIELD EMISSION/ION MULTIPLICATION BREAK-DOWN WILL TRIGGER BREAKDOWN OF THE TWO ADJACENT ELECTRICAL GAPS. THUS CURRENT DIVERSION WILL TAKE PLACE, AND MORE IMPORTANTLY, IF THE INCIPIENT TUBE BREAKDOWN TRIGGERS A COMPLETE ACCELERATOR FLASH-OVER, THE EXTERNAL GAP TO THESE ELECTRODES WILL ALREADY BE CONDUCTING AND WILL DIVERT THE STORED ENERGY OF THE ACCELERATOR AWAY FROM THE VACUUM GAP.