Field emission ionization gauge with restricted line of sight between field emissionanode and ion collector

Claim 1

AN IONIZATION DEVICE ADAPTED TO PRODUCE OR MEASURE ULTRA HIGH VACUA IN A CLOSED SYSTEM OF THE ORDER OF 10-13 MM. HG OR LESS AND COMPRISING AN EVACUABLE ENVELOPE ADAPTED TO BE CONNECTED TO A VACUUM SYSTEM AND INCLUDING: (A) A CYLINDRICAL ANODE MEMBER; (B) A CATHODE AND SHIELD MEMBER AT ONE END OF SAID ANODE MEMBER AND ELECTRICALLY INSULATED THEREFROM, (B1) SAID CATHODE AND SHIELD MEMBER HAVING A SMALL APERTURE AT SUBSTANTIALLY THE CENTER THEREOF WHICH IS SUBSTANTIALLY ALONG THE LONGITUDINAL AXIS OF SAID CYLINDRICAL ANODE MEMBER; (C) AN ION COLLECTOR MEANS AT THE END OF SAID ANODE OPPOSITE FROM SAID CATHODE AND SHIELD MEMBER AND ELECTRICALLY INSULATED THEREFROM; (D) SAID ANODE MEMBER, SAID CATHODE AND SHIELD MEMBER AND SAID ION COLLECTOR MEANS DEFINING AN INTERACTION SPACE WHEREIN ELECTRONS, MAY DESCRIBE ELONGATED CURVILINEAR PATHS WITH A HIGH PROBABILITY OF COLLISION WITH GAS MOLECULES TO PRODUCE POSITIVE IONS, (E) MEANS EXTERNAL OF SAID INTERACTION SPACE FOR INJECTING ELECTRONS THROUGH SAID APERTURED CATHODE AND SHIELD MEMBER AND INCLUDING (E1) A POINTED FIELD EMISSION CATHODE, AND (E2) A CYLINDRICAL FIELD EMISSION ANODE SURROUNDING SAID FIELD EMISSION CATHODE AND LOCATED SUBSTANTIALLY ON SAID LONGITUDINAL AXIS, SAID FIELD EMISSION ANODE HAVING A CENTRAL APERTURE ON SAID AXIS LARGER THAN SAID SMALL APERTURE, WHEREBY THE AREA OF SAID ION COLLECTOR WITHIN LINE OF SIGHT OF SAID FIELD EMISSION ANODE IS MINIMIZED.