ION SOURCE USING HEATED CATHODE AND ELECTROMAGNETIC CONFINEMENT

• US 20140183376A1
• Filed: 12/27/2012
• Published: 07/03/2014
• Est. Priority Date: 12/27/2012
• Status: Active Grant

• Current Assignee: Schlumberger Technology Corporation (Schlumberger NV)
• Original Assignee: Schlumberger Technology Corporation (Schlumberger NV)
• Inventors: Perkins, Luke
• Granted Patent: US 9,633,813 B2
• Time in Patent Office: Days
• US Class Current: 250/424
• CPC Class Codes: H01J 27/205 with electrons, e.g. electron impact ionisation, electron attachment

Abstract

An ion source for use in a radiation generator tube includes a back passive cathode electrode, a passive anode electrode downstream of the back passive cathode electrode, a magnet adjacent the passive anode electrode, and a front passive cathode electrode downstream of the passive anode electrode. The front passive cathode electrode and the back passive cathode electrode define an ionization region therebetween. At least one ohmically heated cathode is configured to emit electrons into the ionization region. The back passive cathode electrode and the passive anode electrode, and the front passive cathode electrode and the passive anode electrode, have respective voltage differences therebetween, and the magnet generating a magnetic field, such that a Penning-type trap is produced to confine the electrons to the ionization region. At least some of the electrons in the ionization region interact with an ionizable gas to create ions.

Claims

1. An ion source for use in a radiation generator tube comprising:

a back passive cathode electrode;

a passive anode electrode downstream of the back passive cathode electrode;

a magnet adjacent the passive anode electrode;

a front passive cathode electrode downstream of the passive anode electrode, the front passive cathode electrode and the back passive cathode electrode and defining an ionization region therebetween; and

at least one ohmically heated cathode configured to emit electrons into the ionization region;

the back passive cathode electrode and the passive anode electrode, and the front passive cathode electrode and the passive anode electrode, having respective voltage differences therebetween, and the magnet generating a magnetic field, such that a Penning-type trap is produced to confine the electrons to the ionization region;

at least some of the electrons in the ionization region interacting with an ionizable gas to create ions.

2. The ion source of claim 1, wherein the at least one ohmically heated cathode comprises a plurality thereof.

3. The ion source of claim 1, wherein the at least one ohmically heated cathode comprises a ring.

4. The ion source of claim 1, further comprising an extractor electrode downstream of the front passive cathode electrode.

5. The ion source of claim 4, wherein the extractor electrode has an opening defined therein;

and

further comprising a dome screen extending across the opening of the extractor electrode.

6. The ion source of claim 1, wherein the magnet comprises a permanent magnet.

7. The ion source of claim 1, wherein the magnet comprises an electromagnet.

8. The ion source of claim 1, further comprising a sealed envelope surrounding the back passive cathode electrode, passive anode electrode, magnet, front passive cathode electrode, and at least one ohmically heated cathode.

9. The ion source of claim 1, wherein the electric fields results in the electrons having an energy sufficient to ionize hydrogen, deuterium or tritium gas.

10. The ion source of claim 1, wherein the at least one ohmically heated cathode is a dispenser cathode.

11. A well logging instrument comprising:

a sonde housing;

a radiation generator tube carried by the sonde housing and comprising

an ion source comprising

a back passive cathode electrode;

a passive anode electrode downstream of the back passive cathode electrode;

a magnet adjacent the passive anode electrode;

a front passive cathode electrode downstream of the passive anode electrode, the front passive cathode electrode and the back passive cathode electrode defining an ionization region therebetween;

at least one ohmically heated cathode configured to emit electrons into the ionization region;

the back passive cathode electrode and the passive anode electrode, and the front passive cathode electrode and the passive anode electrode, having respective voltage differences therebetween, and the magnet generating a magnetic field, such that a Penning-type trap is produced to confine the electrons to the ionization region;

at least some of the electrons in the ionization region interacting with an ionizable gas to create ions;

a suppressor electrode downstream of the ion source; and

a target downstream of the suppressor electrode;

the suppressor electrode having a potential such that a resultant electric field between the front passive cathode electrode and suppressor electrode accelerates the ions generated by the ion source toward the target.

12. The well logging instrument of claim 11, wherein the at least one ohmically heated cathode comprises a plurality thereof.

13. The well logging instrument of claim 11, further comprising an extractor electrode downstream of the front passive cathode electrode.

14. The well logging instrument of claim 11, wherein the magnet comprises a permanent magnet or an electromagnet.

15. An ion source for use in a radiation generator comprising:

a gas reservoir to emit an ionizable gas;

at least one ohmically heated cathode to emit electrons; and

a penning device to confine the electrons in a penning-style trap;

at least some of the electrons in the penning-style trap interacting with the ionizable gas to thereby generate ions.

16. The ion source of claim 15, wherein the penning device comprises a back passive cathode electrode, a passive anode electrode downstream of the back passive cathode electrode, a magnet adjacent the passive anode electrode, and a front passive cathode electrode downstream of the passive anode electrode;

and wherein the at least one ohmically heated cathode is carried by the back passive cathode electrode.

17. The ion source of claim 15, wherein the penning device comprises a back passive cathode electrode, a passive anode electrode downstream of the back passive cathode electrode, a magnet adjacent the passive anode electrode, and a front passive cathode electrode downstream of the passive anode electrode;

and wherein the at least one ohmically heated cathode is carried by the front passive cathode electrode.

18. The ion source of claim 15, wherein the penning device comprises a back passive cathode electrode, a passive anode electrode downstream of the back passive cathode electrode, a magnet adjacent the passive anode electrode, a front passive cathode electrode downstream of the passive anode electrode, and a sealed envelope surrounding the back passive cathode electrode, passive anode electrode, magnet, front passive cathode electrode, and at least one ohmically heated cathode;

and wherein the at least one ohmically heated cathode is carried by the sealed envelope.

19. A method of operating an ion source having a back passive cathode electrode, a passive anode electrode downstream of the back passive cathode electrode, a magnet adjacent the passive anode electrode, and a front passive cathode electrode downstream of the passive anode electrode, the method comprising:

emitting electrons into an ionization region defined between the back and front passive cathode electrodes, using at least one ohmically heated cathode;

producing a Penning-type trap to confine the electrons to the ionization region by generating respective voltage differences between the back passive cathode electrode and the passive anode electrode, and the front passive cathode electrode and the anode, and by generating a magnetic field with the magnet;

generating ions via interactions between at least some of the electrons and an ionizable gas as the electrons travel in the ionization region.

20. The method of claim 19, wherein the at least one ohmically heated cathode comprises a plurality thereof.

21. The method of claim 19, further comprising accelerating the ions out of the ion source using an extractor electrode downstream of the front passive cathode electrode.

22. The method of claim 19, wherein the magnet comprises a permanent magnet.

23. The method of claim 19, wherein the magnet comprises an electromagnet.