FIELD EMISSION ION SOURCE NEUTRON GENERATOR

• US 20160216400A1
• Filed: 12/31/2013
• Published: 07/28/2016
• Est. Priority Date: 12/31/2013
• Status: Active Grant

• Current Assignee: Halliburton Energy Services Incorporated (Halliburton Company)
• Original Assignee: Halliburton Energy Services Incorporated (Halliburton Company)
• Inventors: Navarro-Sorroche, Juan, Guo, Weijun
• Granted Patent: US 10,408,968 B2
• Time in Patent Office: Days
• US Class Current: 1/1
• CPC Class Codes: G01V 5/10 using neutron sources neutron generating tubes H05H5/00; neutron sources using isotopes G21G4/00
• CPC Class Codes: G21G 4/02 Neutron sources
• CPC Class Codes: H05H 3/06 Generating neutron beams targets for producing nuclear reactions H05H6/00; neutron sources G21G4/02

Abstract

A well logging tool includes a neutron generator having an ion source cathode comprising a nano-structure field emission (FE) array for producing a charged particle current routed through an ionizable gas, thus generating ions by electron impact ionization of the gas. The nanostructures can be provided by bundles of silicon nanotips grown on a substrate. The FE array can be provided on an axially facing substrate located co-axially in an elongate housing, with the charged particle current directed from the centrally located FE array to a co-axial annular anode and having axial and radial directional components.

Claims

1. A neutron generator comprising:

a housing configured for incorporation in a subsurface logging tool, the housing defining an ion source chamber;

a gas source configured to deliver ionizable gas to the ion source chamber; and

a field emitter array configured to deliver charged particles to the ion source chamber for interacting with the ionizable gas to produce ions usable for a fusion reaction that results in neutron emission from the neutron generator, the field emitter array comprising multiple nano-emitters.

2. The neutron generator of claim 1, wherein the multiple nano-emitters comprise multiple nanotips, each nanotip comprising an elongate filament which is substantially aligned with a longitudinal axis of the housing.

3. The neutron generator of claim 1, wherein the field emitter array comprises multiple silicon nanotips on a substrate located in the ion source chamber.

4. The neutron generator of claim 1, wherein the housing is elongate and is configured to be insertable lengthwise in a borehole, the field emitter array being substantially co-axial with a longitudinal axis of the housing, the neutron generator further comprising an ion source configured to accelerate charged particles delivered by the field emitter array at least partially radially outwards through the ion source chamber and towards a radial periphery of the ion source chamber.

5. The neutron generator of claim 1, wherein the housing is elongate and is configured to be insertable lengthwise in a borehole, the field emitter array being substantially co-axial with a longitudinal axis of the housing, the neutron generator further comprising an anode that is radially offset from the longitudinal axis and is configured to attract charged particles delivered to the ion source chamber by the field emitter array.

6. The neutron generator of claim 5, wherein the anode comprises an annular element co-axial with the longitudinal axis of the housing.

7. The neutron generator of claim 6, wherein an inner radius of the annular anode element is greater than a radially outer extremity of the field emitter array.

8. The neutron generator of claim 5, wherein the field emitter array comprises a substrate providing a substantially circular substrate surface on which the multiple nano-emitters are supported, the substrate being co-axial with the longitudinal axis of the housing and extending transversely thereto.

9. The neutron generator of claim 5, wherein the field emitter array and the anode form part of a magnet-free ion source configured to produce the ions without a permanent magnet located adjacent the ion source chamber.

10. The neutron generator of claim 5, further comprising:

an ion target carrying target particles for forming part of the fusion reaction in response to energetic impact of ions with the ion target; and

an ion accelerator configured to extract the ions from the ion source chamber, and to accelerate the extracted ions onto the ion target.

11. The neutron generator of claim 5, wherein the field emitter array forms part of a field emitter device, the neutron generator further comprising a control arrangement configured to apply an ion source voltage pulse between the field emitter device and the anode to cause ignition of the ionization of the ionizable gas in the ion source chamber, the field emitter device serving as ion source cathode.

12. The neutron generator of claim 11, wherein the field emitter device comprises an embedded extraction grid coupled to the control arrangement.

13. The neutron generator of claim 11, wherein the ion source voltage pulse has an amplitude of 500 V or less.

14. The neutron generator of claim 13, wherein a turn-on/turn-of delay for an ion source comprising the field emitter device and the anode is smaller than 1 μ

s.

15. The neutron generator of claim 1, wherein the fusion reaction comprises a deuterium-tritium fusion reaction.

16. A method comprising:

incorporating a neutron generator in a subsurface logging tool, the neutron generator having a housing that defines an ion source chamber;

delivering an ionizable gas to the ion source chamber;

causing a field emitter array comprising multiple nano-emitters to deliver energetic charged particles to the ion source chamber, thereby causing ion production in the ion source chamber; and

using the ions in a fusion reaction that results in neutron emission from the neutron generator.

17. The method of claim 16, wherein the field emitter array comprises multiple silicon nanotips on a substrate located in the ion source chamber.

18. The method of claim 16, further comprising inserting the subsurface logging tool into a borehole such that the housing extends lengthwise along the borehole, the multiple nano-emitters being supported on a substantially circular substrate surface co-axial with and transverse to a longitudinal axis of the housing, the logging tool further comprising an annular anode co-axial with the substrate surface and located in the ion source chamber, wherein the causing of the field emitter array to deliver the energetic charged particles to the ion source chamber comprises applying an ion source voltage pulse between the field emitter array and the annular anode.

19. The method of claim 18, wherein the ion source voltage pulse has an amplitude of 500 V or less.

20. The method of claim 18, wherein a turn-on/turn-of delay for electron impact ionization in the ion source chamber is smaller than 1 μ

s.

21. A subsurface logging tool comprising:

a body configured for location in a borehole; and

a neutron generator housed by the body for generating and emitting energetic neutrons, the neutron generator comprising

a housing that defines an ion source chamber;

a gas source configured to deliver ionizable gas to the ion source chamber; and

a field emitter array configured to deliver energetic ions to the ion source chamber for interacting with the ionizable gas to produce ions usable for a fusion reaction that results in neutron emission from the neutron generator, the field emitter array comprising multiple nano-emitters.