Electron discharge device

Claim 1

AN ELECTRON DISCHARGE DEVICE COMPRISING AN ELECTRON GUN AND TARGET, SAID ELECTRON GUN COMPRISING AN ELECTRON EMISSIVE SOURCE, A FIRST GRID, A SECOND GRID AND A THIRD GRID ARRANGED IN THE DIRECTION OF ELECTRON TRAVEL TOWARDS SAID TARGET, SAID FIRST GRID COMPRISING A TUBULAR MEMBER HAVING AN END WALL FORMED TO PROVIDE AN APERTURE ALIGNED WITH SAID ELECTRON SOURCE, THE WALL SURROUNDING SAID APERTURE BEING OF REDUCED THICKNESS AS COMPARED WITH THE REMAINING PORTION OF SAID END WALL, A SECOND GRID COMPRISING A TUBULAR MEMBER AND HAVING AN END WALL ON THE END OF SAID TUBULAR MEMBER FACING SAID FIRST GRID, THE CENTRAL PORTION OF SAID END WALL OF SAID SECOND GRID FORMED TO PROVIDE AN APERTURE ALIGNED WITH THE APERTURE IN SAID FIRST GRID AND CLOSER TO THE FIRST GRID THAN THE REMAINING PORTION OF THE END WALL OF SAID SECOND GRID, THE DIAMETER OF THE APERTURE IN SAID SECOND GRID BEING LESS THAN THE DIAMETER OF THE APERTURE IN SAID FIRST GRID, A SHIELD MEMBER PROVIDED WITHIN THE TUBULAR PORTION OF SAID SECOND GRID ELECTRODE HAVING A DIAPHRAGM WITH AN APERTURE THEREIN AND ALIGNED WITH SAID APERTURE IN SAID SECOND GRID, SAID SHIELD MEMBER ELECTRICALLY CONNECTED TO SAID END WALL OF SAID SECOND GRID WITH THE APERTURE IN SAID SECOND GRID AND SAID SHIELD SPACED APART BY A DISTANCE LESS THAN .6 OF THE DIAMETER OF THE APERTURE IN SAID SHIELD, THE DIAMETER OF THE APERTURE IN SAID SHIELD MEMBER BEING GREATER THAN THE DIAMETER OF THE APERTURE IN SAID SECOND GRID, SAID THIRD ELECTRODE COMPRISING AN OUTER TUBULAR MEMBER AND AN INNER TUBULAR MEMBER, SAID INNER TUBULAR MEMBER TAPERED TO PROVIDE A SMALLER ENTRANCE APERTURE ADJACENT SAID SECOND GRID AND ALIGNED WITH THE APERTURE OF SAID SECOND GRID, THE DIAMETER OF THE ENTRANCE APERTURE OF SAID THIRD GRID BEING LESS THAN THE DIAMETER OF THE TUBULAR PORTION OF SAID SECOND GRID AND THE SPACING BETWEEN THE APERTURE IN THE SHIELD MEMBER AND THE APERTURE IN SAID THIRD GRID ELECTRODE GREATER THAN THREE TIMES THE DIAMETER OF THE APERTURE IN SAID SHIELD MEMBER.