Axial ci source - off-axis electron beam

Abstract

An ion source includes an electron generator, an ionization chamber, and a magnetic field. The electron generator is configured to produce electrons. The ionization chamber has an electron entrance aperture through a first wall, an ion exit aperture through a second wall, and an axis. The ionization chamber is configured to produce ions. The magnetic field is arranged to confine electrons in a beam directed through the electron entrance aperture, in a direction within 45 degrees of parallel to the axis, and towards a location displaced from the ion exit aperture.

1 . An ion source comprising:
 an electron generator configured to produce electrons;   an ionization chamber having an electron entrance aperture through a first wall, an ion exit aperture through a second wall, and an axis, the ionization chamber configured to produce ions;   a magnetic field arranged to confine electrons in a beam directed through the electron entrance aperture, in a direction within 45 degrees of parallel to the axis, and towards a location displaced from the ion exit aperture; and   an ion optic configured to direct ions exiting the ion exit aperture in an ion beam along the axis.   
     
     
         2 . The ion source of  claim 1  wherein the ionization chamber is configured to produce ions by chemical ionization. 
     
     
         3 . The ion source of  claim 1  wherein the location is on the second wall. 
     
     
         4 . The ion source of  claim 1  wherein the electron beam is parallel to the axis but offset from the ion beam in a direction orthogonal to the axis. 
     
     
         5 . The ion source of  claim 1  wherein the electron beam intersects a line along the direction of the ion beam. 
     
     
         6 . The ion source of  claim 1  wherein the ionization chamber further includes a recess on the second wall and displaced from the ion exit aperture, and the electron beam is directed towards the recess. 
     
     
         7 . A mass spectrometer comprising:
 an ion source of  claim 1 ; and   a mass analyzer.   
     
     
         8 . A method comprising:
 generating electrons;   directing electrons in a beam through an electron entrance aperture through a first wall of an ionization chamber and towards a location displaced from an ion exit aperture through a second wall of the ionization chamber, and in a direction within 45 degrees of parallel to an axis of the ionization chamber;   producing ions within the ionization chamber; and   directing ions as a beam through the ion exit aperture and in a direction parallel to the axis of the ionization chamber.   
     
     
         9 . The method of  claim 8  wherein producing ions within the ionization chamber includes producing ions by chemical ionization. 
     
     
         10 . The method of  claim 8  wherein the location is on the second wall. 
     
     
         11 . The method of  claim 8  wherein directing the electron beam includes directing the electron beam in a direction parallel to the axis but offset from the ion beam in a direction orthogonal to the axis. 
     
     
         12 . The method of  claim 8  wherein directing the electron beam includes directing the electron beam to intersect a line along the direction of the ion beam. 
     
     
         13 . The method of  claim 8  wherein directing the electron beam includes directing the electron beam towards a recess on the second wall of the ionization chamber and displaced from the ion exit aperture. 
     
     
         14 . An ion source comprising:
 an electron generator configured to produce electrons;   an ionization chamber having an electron entrance aperture through a first wall and an ion exit aperture through a second wall, the ionization chamber configured to produce ions;   a magnetic field arranged to confine electrons in a beam directed through the electron entrance aperture;   an electron dispersive mechanism configured to disperse the electrons within the ionization chamber.   
     
     
         15 . The ion source of  claim 14  wherein the ionization chamber is configured to produce ions by chemical ionization. 
     
     
         16 . The ion source of  claim 14  wherein the first wall and the second wall are opposite from one another. 
     
     
         17 . The ion source of  claim 14  wherein the electron dispersive mechanism includes a magnetic shielding configured to reduce the magnetic fields within at least a portion of the ionization chamber. 
     
     
         18 . The ion source of  claim 14  wherein the electron dispersive mechanism includes one or more additional magnets oriented to disrupt the magnetic field. 
     
     
         19 . The ion source of  claim 14  wherein the electron dispersive mechanism includes an electrostatic lens configured to direct electrons away from the ion exit aperture without substantially affecting the ion beam. 
     
     
         20 . A mass spectrometer comprising:
 an ion source of  claim 14 ; and   a mass analyzer.   
     
     
         21 . A method comprising:
 generating electrons;   directing electrons in a beam through an electron entrance aperture of an ionization chamber;   dispersing the electrons within the ionization chamber;   producing ions within the ionization chamber; and   directing the ions as a beam through the ion exit aperture.   
     
     
         22 . The method of  claim 21  wherein producing ions within the ionization chamber includes producing ions by chemical ionization.