NANO-EMITTER ION SOURCE NEUTRON GENERATOR

• US 20160295678A1
• Filed: 12/31/2013
• Published: 10/06/2016
• 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 9,756,714 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 for ion production by electron impact ionization wherein ionization current trajectory is determined by an electric field and an at least partially misaligned magnetic field. The electric field can be provided by an electrode arrangement having a cathode associated with a field emitter array including a multitude of nanoemitters. The magnetic field can be provided by a permanent magnet incorporated in the neutron generator to act transversely to the electric field in at least part of an ion source chamber in which an ionization current emitted by the field emitter array travels through an ionizable gas. Charged particles traveling through the ionizable gas thus follow respective trajectories that are longer than would be the case in the absence of the magnetic field, thereby increasing ionization probability.

Claims

1. A neutron generator comprising:

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

a nano-emitter arrangement comprising multiple nano-emitters located in the ion source chamber and configured for emitting electrons into the ion source chamber;

an electrode arrangement configured to provide an electric field in the ion source chamber for propelling the emitted electrons through the ionizable gas, to cause ion production by electron impact ionization of the ionizable gas; and

a permanent magnet that provides a magnetic field configured to act on the emitted electrons, in at least part of the ion source chamber, in misalignment with the electric field.

2. The neutron generator of claim 1, wherein the permanent magnet is configured to act substantially transversely to the electric field in at least one part of the ion source chamber.

3. The neutron generator of claim 1, wherein the permanent magnet is configured to cause the emitted electrons to travel through the ion source chamber along respective modified trajectories which are longer than respective default trajectories corresponding to electron travel absent the magnetic field.

4. The neutron generator of claim 1, wherein housing has a longitudinal axis configured for disposal lengthwise in the subsurface logging tool, the nano-emitter arrangement being oriented for axial electron emission, and wherein the electrode arrangement is configured such that the electric field has a non-negligible radial component, to propel the emitted electrons at least partially radially outwards relative to the longitudinal axis.

5. The neutron generator of claim 4, wherein the field emitter array comprises a substrate providing a substantially circular substrate on which the multiple nano-emitters are supported, the substrate being co-axial with the longitudinal axis of the housing and extending transversely thereto.

6. The neutron generator of claim 4, wherein the permanent magnet is configured to urge the emitted electrons in a direction which is substantially parallel to the longitudinal axis.

7. The neutron generator of claim 6, wherein the permanent magnet is located co-axially with the longitudinal axis of the ion source chamber.

8. The neutron generator of claim 6, wherein the permanent magnet and the multiple nano-emitters are located at a common longitudinal end of the housing.

9. The neutron generator of claim 6, wherein the electrode arrangement comprises a substantially annular anode co-axial with the longitudinal axis of the ion chamber, the annular anode being axially spaced from the multiple nano-emitters.

10. The neutron generator of claim 9, wherein an inner radius of the annular anode is greater than a radially outer extremity of the circular substrate of the multiple nano-emitters.

11. The neutron generator of claim 9, wherein the multiple nano-emitters provide a field emitter array, the neutron generator further comprising a control arrangement configured to apply an ion source voltage pulse between the field emitter device and the annular anode to generate the electric field and cause ignition of the electron impact ionization, the field emitter array serving at least in part as an ion source cathode.

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

13. The neutron generator of claim 11, 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.

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

15. The neutron generator of claim 1, further comprising:

an target structure holding target molecules for forming part of a fusion reaction in response to energetic impact of ions produced in the ion source chamber with the target structure; and

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

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

17. A subsurface logging tool comprising:

a tool body configured for location in a borehole; and

a neutron generator coupled to the body for generating and emitting energetic neutrons, the neutron generator comprising

a housing defining an ion source chamber for holding an ionizable gas;

a nano-emitter arrangement comprising multiple nano-emitters located in the ion source chamber and configured for emitting electrons into the ion source chamber;

an electrode arrangement configured to provide an electric field in the ion source chamber for propelling the emitted electrons through the ionizable gas, to cause ion production by electron impact ionization of the ionizable gas; and

a permanent magnet that provides a magnetic field configured to act on the emitted electrons, in at least part of the ion source chamber, in misalignment with the electric field.

18. 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 electron emission in the ion source chamber by a nano-emitter arrangement comprising multiple nano-emitters;

propelling emitted electrons through the ionizable gas by providing an electric field in the ion source chamber, thereby causing ion production by electron impact ionization; and

providing in the ion source chamber a magnetic field of a permanent magnet such that the electric field acts on the emitted electrons, in at least part of the ion source chamber, in misalignment with the electric field.

19. The method of claim 18, wherein the providing of the magnetic field causes the emitted electrons to travel through the ion source chamber along respective modified trajectories which are longer than respective default trajectories corresponding to electron travel absent influence of the magnetic field.

20. The method of claim 19, wherein the electron emission is in a direction substantially parallel to a longitudinal axis of the subsurface logging tool, the propelling of the emitted electrons through the ionizable gas by operation of the electric field comprising acceleration of the emitted electrons at least partially in a radially outward direction, wherein providing the magnetic field comprises arranging the magnetic field to urge the emitted electrons axially along the ion source chamber.