Ionization chamber having a potential-well for ion trapping and ion compression

1. An ionization chamber, comprising:

a vessel within which an ionization region is defined, said vessel comprising a first end axially disposed opposite a second end;

an ionization source located at said vessel's first end and configured to generate ions, said ionization source configured to have a first ionization source potential during an ion compression stage;

an ion gate located at said second end and configured to have a first ion gate potential during the ion compression stage; and

a mid-ring electrode located between said ionization source and said ion gate, said mid-ring electrode configured to have, during the ion compression stage, a first mid-ring potential that is less than the first ionization source potential and the first ion gate potential, the first mid-ring potential set at a value to generate a potential well proximate said mid-ring electrode.

2. The ionization chamber of claim 1 , wherein said first ion gate potential is set at a value such that ions are prevented from traveling through said ion gate and from said vessel.

3. The ionization chamber of claim 1 , wherein said first ionization source potential is set at a value such that ions are evacuated from the first end of said vessel.

4. The ionization chamber of claim 1 , wherein the first ionization source potential is equal to the first ion gate potential.

5. The ionization chamber of claim 1 , wherein, during a release stage:

said ionization source is further configured to have a second ionization source potential that is greater than the first ionization source potential;

said mid-ring electrode is further configured to have a second mid-ring potential that is greater than the first mid-ring potential; and

said ion gate further configured to have a second ion gate potential that is less than the second mid-ring potential and the second ionization source potential, wherein the second mid-ring potential and the second ion gate potential cooperate to move a pulse of the ions through said ion gate and from said second end of said vessel.

6. The ionization chamber of claim 5 , wherein, during the release stage, a difference between the second ionization source potential and the second mid-ring potential is less than a difference between the second mid-ring potential and the second ion gate potential.

7. The ionization chamber of claim 1 , wherein said mid-ring electrode is further configured to have a potential gradient over an axial dimension of said mid-ring electrode.

8. The ionization chamber of claim 7 , wherein the potential gradient is axially asymmetrical.

9. The ionization chamber of claim 1 , wherein said ion gate comprises a conductive grid disposed between the ionization region and a drift region.

10. A method of compressing ions, said method comprising:

generating ions at an ionization source within an ionization chamber;

charging a mid-ring electrode to a first mid-ring potential to generate a potential well relative to a first ionization source potential and a first ion gate potential, wherein the potential well is configured to collect the ions;

charging an ion gate to the first ion gate potential to prevent the ions from traveling through the ion gate and into a drift region, wherein the mid-ring electrode is located between the ionization source and the ion gate; and

charging the ionization source to the first ionization source potential, wherein the first ionization source potential and the first ion gate potential are greater than the first mid-ring potential.

11. The method of claim 10 further comprising:

charging the mid-ring electrode to a second mid-ring potential that is greater than the first mid-ring potential; and

charging the ion gate to a second ion gate potential that is less than the second ionization source potential and the second mid-ring potential to pulse the ions into the drift region.

12. The method of claim 11 , wherein the second ion gate potential is equal to the first ion gate potential.

13. The method of claim 11 , wherein the second ionization source potential and the second mid-ring potential are greater than the second ion gate potential, such that a pulse of the ions travel through the ion gate.

14. A method of compressing ions, said method comprising:

generating ions at an ionization source within an ionization chamber;

charging a mid-ring electrode to a first mid-ring potential to generate a potential well relative to a first ionization source potential and a first ion gate potential, wherein the potential well is configured to collect the ions and wherein charging the mid-ring electrode to the first mid-ring potential comprises charging the mid-ring electrode with a potential gradient over a length of the mid-ring electrode in an axial dimension of the ionization chamber;

charging an ion gate to the first ion gate potential to prevent the ions from traveling through the ion gate and into a drift region, wherein the mid-ring electrode is located between the ionization source and the ion gate.

15. An ion mobility spectrometer (IMS) device, comprising:

a drift tube defining a drift region therein; and

an ionization chamber defining an ionization region therein, said ionization chamber comprising:

an ionization source located at a first end of said ionization region and configured to generate ions, said ionization source configured to have a first ionization source potential during an ion compression stage;

an ion gate located adjacent to said drift tube and at a second end of said ionization region, said ion gate configured to have a first ion gate potential during the ion compression stage; and

a mid-ring electrode located between said ionization source and said ion gate, said mid-ring electrode configured to have, during the ion compression stage, a first mid-ring potential that is less than the first ionization source potential and the first ion gate potential, the first mid-ring potential configured to generate a potential well, proximate said mid-ring electrode, where the ions collect during the ion compression stage.

16. The IMS device of claim 15 , wherein, during a release stage:

said ionization source is further configured to have a second ionization source potential that is greater than the first ionization source potential;

said mid-ring electrode is further configured to have a second mid-ring potential that is greater than the first mid-ring potential; and

said ion gate is further configured to have a second ion gate potential that is less than the second ionization source potential and the second mid-ring potential, wherein the second ionization source potential, the second mid-ring potential, and the second ion gate potential cooperate to move a pulse of the ions through said ion gate and into said drift region.

17. The IMS device of claim 16 , wherein, during the release stage, a difference between the second ionization source potential and the second mid-ring potential is less than a difference between the second mid-ring potential and the second ion gate potential.

18. The IMS device of claim 15 , wherein said mid-ring electrode is further configured to have a potential gradient over an axial dimension of said mid-ring electrode.

19. The IMS device of claim 15 , wherein said first ion gate potential is set at a value such that ions are prevented from traveling through said ion gate and into said drift region.

20. The IMS device of claim 15 , wherein said first ionization source potential is set at a value such that ions are evacuated from the first end of said ionization region.

21. The IMS device of claim 15 , wherein said ion gate comprises a Bradbury-Nielson gate.