Electrostatic focussing devices

Claim 1

AN ELECTROSTATIC FOCUSSING DEVICE INCLUDING A PAIR OF PERIODIC METAL STRUCTURES DISPOSED WITH THEIR LENGTHS SUBSTANTIALLY PARALLEL TO EACH OTHER SO AS TO DEFINE BETWEEN THEM A SPACE THROUGH WHICH AN ELECTRON BEAM MAY TRAVEL, ELEMENTS OF ONE OF THE PERIODIC STRUCTURES BEING RESPECTIVELY DISPOSED OPPOSITE AT LEAST PARTS OF ELEMENTS OF THE OTHER PERIODIC STRUCTURE, AND EACH STRUCTURE BEING SO CONSTRUCTED THAT THE ELEMENTS OF THE STRUCTURE ARE PERMANENTLY ELECTRICALLY CONNECTED TOGETHER, AND TWO FURTHER METAL STRUCTURES EXTENDING ON EITHER SIDE OF AN ELECTRICALLY INSULATED FROM THE PAIR OF PERIODIC STRUCTURES SO THAT EACH PERIODIC STRUCTURE LIES BETWEEN THE OTHER PERIODIC STRUCTURE AND ONE OF SAID FURTHER METAL STRUCTURES, THE ARRANGEMENT BEING SUCH THAT, UPON APPLYING SUITABLE POTENTIALS TO THE PERIODIC METAL STRUCTURES AND TO THE FURTHER METAL STRUCTURES SO THAT EACH OF THE PERIODIC STRUCTURES IS AT A POSITIVE POTENTIAL WITH RESPECT TO THE FURTHER METAL STRUCTURES AND UPON PROJECTING AN ELECTRON BEAM IN A SUITABLE MANNER INTO SAID SPACE AT ONE END, THE BEAM TRAVELS THROUGH SAID SPACE GENERALLY IN A DIRECTION PARALLEL TO THE LENGTHS OF THE STRUCTURES, THE BEAM HAVING AN UNDULATORY FORM SUCH THAT IT ALTERNATELY APPROACHES AND RECEDES FROM EACH PERIODIC STRUCTURE.