Ionization Chamber Having a Potential-Well for Ion Trapping and Ion Compression

Abstract

An ionization chamber. The ionization chamber includes a vessel, an ionization source, an ion gate, and a mid-ring electrode. The vessel defines an ionization region. The vessel includes a first end axially disposed opposite a second end. The ionization source is located at the first end and generates ions. The ion gate is located at the second end of the vessel. The mid-ring electrode is located between the ionization source and the ion gate. During an ion compression stage, the ionization source is charged to a first ionization source potential, the ion gate is charged to a first ion gate potential, and the mid-ring electrode is charged to 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 is configured to generate a potential well proximate the mid-ring electrode. The ions collect at the potential well.

What is claimed is: 
     
         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 be charged to a first ionization source potential during an ion compression stage;   an ion gate located at said second end and configured to be charged to 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 be charged, during the ion compression stage, to a first mid-ring potential that is less than the first source potential and the first ion gate potential, the first mid-ring potential configured to generate a potential well, proximate said mid-ring electrode.   
     
     
         2 . The ionization chamber of  claim 1 , wherein said ion gate is further configured to be charged to the first ion gate potential to prevent the ions from traveling through said ion gate and from said vessel. 
     
     
         3 . The ionization chamber of  claim 1 , wherein said ionization source is further configured to be charged to the first ionization source potential to evacuate the ions 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 be charged to a second ionization source potential that is greater than the first ionization source potential;   said mid-ring electrode is further configured to be charged to a second mid-ring potential that is greater than the first mid-ring potential; and   said ion gate further configured to be charged to 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 are configured to 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 be charged to 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, the potential well configured to collect the ions; and   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.   
     
     
         11 . The method of  claim 10  further comprising 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. 
     
     
         12 . The method of  claim 11  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. 
 
     
     
         13 . The method of  claim 12 , wherein the second ion gate potential is equal to the first ion gate potential. 
     
     
         14 . The method of  claim 12 , 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. 
     
     
         15 . The method of  claim 10 , 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. 
     
     
         16 . 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 be charged to 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 be charged to 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 be charged, during the ion compression stage, to 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.   
     
     
         17 . The IMS device of  claim 16 , wherein, during a release stage:
 said ionization source is further configured to be charged to a second ionization source potential that is greater than the first ionization source potential;   said mid-ring electrode is further configured to be charged to a second mid-ring potential that is greater than the first mid-ring potential; and   said ion gate is further configured to be charged to 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 are configured to cooperate to move a pulse of the ions through said ion gate and into said drift region.   
     
     
         18 . The IMS device of  claim 17 , 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. 
     
     
         19 . The IMS device of  claim 16 , wherein said mid-ring electrode is further configured to be charged to a potential gradient over an axial dimension of said mid-ring electrode. 
     
     
         20 . The IMS device of  claim 16 , wherein said ion gate is further configured to be charged to the first ion gate potential to prevent the ions from traveling through said ion gate and into said drift region.