Field-ionization neutron generator
First Claim
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1. A neutron generator comprising:
- a closed housing containing an ionizable gas, the closed housing defining a first portion and a second portion along a longitudinal axis thereof;
a field-ionization structure arranged along an inner surface of the closed housing in the first portion, wherein application of an electrical voltage to the field-ionization structure ionizes the ionizable gas, wherein the field-ionization structure comprises an array of nanotips disposed on a cylindrical substrate and a field-ionization grid disposed concentrically interior to the cylindrical substrate, and wherein a set of nanotips of the array of nanotips are located at openings in the field-ionization grid and aligned with the field-ionization grid;
a cylindrical accelerating grid placed about the longitudinal axis in the first portion, wherein holding the cylindrical accelerating grid at a first negative electric potential relative to the field-ionization grid causes accumulation of ions in the grid; and
a target cathode disposed at an end of the second portion that is distal to the first portion, wherein holding the target cathode at a second negative electrical potential relative to the cylindrical accelerating grid extracts ions from the cylindrical accelerating grid and accelerates them towards the target cathode to thereby cause fusion reactions between the ions and target atoms contained in the target cathode.
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Abstract
Described herein are neutron generators that employ direct field ionization of ionizable fusion gases, as well as well-logging tools and methods that utilize such neutron generators. In various embodiments, the neutron generator includes a cylindrical field-ionization structure distributed around the inner surface of a tubular housing, and a cylindrical ion-accelerating grid disposed about the longitudinal axis concentrically to the field-ionization structure. Ions generated by the field-ionization structure may accumulate inside the ion-accelerating grid, from which they can be axially extracted and accelerated towards a fusion target. Additional tools, systems, and methods are disclosed.
15 Citations
24 Claims
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1. A neutron generator comprising:
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a closed housing containing an ionizable gas, the closed housing defining a first portion and a second portion along a longitudinal axis thereof; a field-ionization structure arranged along an inner surface of the closed housing in the first portion, wherein application of an electrical voltage to the field-ionization structure ionizes the ionizable gas, wherein the field-ionization structure comprises an array of nanotips disposed on a cylindrical substrate and a field-ionization grid disposed concentrically interior to the cylindrical substrate, and wherein a set of nanotips of the array of nanotips are located at openings in the field-ionization grid and aligned with the field-ionization grid; a cylindrical accelerating grid placed about the longitudinal axis in the first portion, wherein holding the cylindrical accelerating grid at a first negative electric potential relative to the field-ionization grid causes accumulation of ions in the grid; and a target cathode disposed at an end of the second portion that is distal to the first portion, wherein holding the target cathode at a second negative electrical potential relative to the cylindrical accelerating grid extracts ions from the cylindrical accelerating grid and accelerates them towards the target cathode to thereby cause fusion reactions between the ions and target atoms contained in the target cathode. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10)
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11. A tool comprising:
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a neutron generator comprising, contained within a closed housing defining a first portion and a second portion along a longitudinal axis thereof; a field-ionization structure arranged along an inner surface of the closed housing in the first portion, wherein application of an electrical voltage on the field-ionization structure ionizes an ionizable gas contained within the closed housing, wherein the field-ionization structure comprises an array of nanotips disposed on a cylindrical substrate and a field-ionization grid disposed concentrically interior to the cylindrical substrate, and wherein a set of nanotips of the array of nanotips are located at openings in the field-ionization grid and aligned with the field-ionization grid; a cylindrical accelerating grid placed about the longitudinal axis in the first portion, wherein holding the cylindrical accelerating grid at a first negative electric potential relative to the field-ionization grid causes accumulation of ions in the grid; a target cathode disposed at an end of the second portion that is distal to the first portion, wherein holding the target cathode at a second negative electrical potential relative to the cylindrical accelerating grid extracts ions from the cylindrical accelerating grid and accelerates them towards the target cathode, and wherein fusion reactions between the ions and target atoms contained in the target cathode generates neutrons; and a radiation detector to detect radiation resulting from interaction of the neutrons with materials outside the tool. - View Dependent Claims (12, 13, 14, 15, 16, 17, 18)
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19. A method comprising:
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disposing a tool in a borehole, the tool comprising a neutron generator that comprises; a closed housing containing an ionizable gas, the closed housing defining a first portion and a second portion along a longitudinal axis thereof; a cylindrical field-ionization structure, arranged along an inner surface of the closed housing in the first portion, for ionizing the ionizable gas upon application of an electrical voltage thereto, wherein the field-ionization structure comprises an array of nanotips disposed on a cylindrical substrate and a field-ionization grid disposed concentrically interior to the cylindrical substrate, and wherein a set of nanotips of the array of nanotips are located at openings in the field-ionization grid and aligned with the field-ionization grid; a cylindrical accelerating grid, placed about the longitudinal axis in the first portion, wherein ions accumulate in the cylindrical accelerating grid when the cylindrical accelerating grid is held at a first negative electric potential relative to the field-ionization grid; and a target cathode, disposed at an end of the second portion that is distal to the first portion, wherein holding the target cathode at a negative electrical potential relative to the cylindrical accelerating grid extracts ions from the cylindrical accelerating grid and accelerates them towards the target cathode to thereby cause fusion reactions between the ions and target atoms contained in the target cathode; and operating the neutron generator in a pulsed mode to generate neutron pulses by fusion of the ionized gas with the target atoms. - View Dependent Claims (20, 21, 22, 23, 24)
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Specification