DEFLECTORS FOR ION BEAMS AND MASS SPECTROMETRY SYSTEMS COMPRISING THE SAME
Provided are ion detectors and systems that may employ such ion detectors such as mass spectrometers and other instruments. The ion detectors include a deflector that serves to generate an electric field with designed shape and strength that causes the ions passing into the detector to move along a deflection path. By selectively deflecting the charged ions from an initial propagation axis, the deflector effectively removes unwanted neutral particles from the ion path and reduces background in the resulting spectra.
1 . An ion detector assembly comprising:
a first particle shield comprising an ion entry opening for receiving an ion beam propagating along a first propagation axis;
a deflector configured to generate an electric field in a deflection region that deflects the ion beam out of alignment with the first propagation axis along a deflection path;
a second particle shield comprising an ion exit opening; and
a detection element configured to convert and multiply the ion beam to electrons after deflection via the deflector, wherein:
the first particle shield extends at an angle relative to the second particle shield,
the first particle shield and the second particle shield define a corner region, and
the deflector comprises:
a first rear surface extending proximate to the first particle shield;
a second rear surface extending proximate to the second particle shield,
a vertex where the first rear surface meets the second rear surface, the vertex being disposed proximate to the corner region; and
a curved deflection surface opposite the vertex and extending between the first rear surface and the second rear surface.
2 . The ion detector assembly of claim 1 , wherein the first rear surface extends parallel to the first particle shield and the second rear surface extends parallel to the second particle shield.
3 . The ion detector assembly of claim 1 , wherein a portion of the deflection path extends at a deflection angle of at least 90° relative to the first propagation axis.
4 . The ion detector assembly of claim 1 , wherein within the deflection region the electric field is configured to cause the deflection path to comprise a deflection radius with an end disposed at a vertex.
5 . The ion detector assembly of claim 4 , wherein:
at least a portion of the curved deflection surface comprises a deflector radius of curvature, as measured from the vertex; and
the deflector radius of curvature is less than a minimal deflection radius of curvature r dmin .
6 . The ion detector assembly of claim 5 , wherein the deflector radius of curvature is greater than or equal to half of a minimal deflection radius of curvature r dmin .
7 . The ion detector assembly of claim 1 , wherein the deflector is a quarter of a sphere centered on the vertex, or wherein the deflector is a quarter of an ellipsoid centered on the vertex, or wherein the deflector comprises a quarter of a cylinder centered on the vertex.
8 . The ion detector assembly of claim 1 , wherein the deflector comprises a cross-sectional area that varies as a function of position along the vertex.
9 . The ion detector assembly of claim 8 , wherein a center of the ion entry opening and a center of the ion exit opening are disposed in a deflection plane containing the cross-sectional area.
10 . A mass spectrometry system comprising:
an ion source generating an ion beam;
a mass analyzer configured to guide the ion beam along a first propagation axis; and
an ion detector assembly comprising:
a pair of particle shields extending at an angle to one another and forming a corner region, the pair of particle shields comprising an ion entry opening for receiving the ion beam and an ion exit opening;
a deflector configured to generate an electric field in a deflection region that deflects the ion beam out of alignment with the first propagation axis along a deflection path extending through the ion exit opening, the deflector comprising a pair of rear surfaces and a vertex where the pair of rear surfaces meet; and
a detection element configured to generate electronic signals from the ion beam after deflection via the deflector, wherein the electric field generated by the deflector comprises iso-potential lines that extend within 10° of perpendicular to one of the particle shields of the pair of particle shields in an area proximate to the ion exit opening.
11 . The mass spectrometry system of claim 10 , further comprising a grounded enclosure configured to shape the iso-potential lines within the deflection region, the grounded enclosure surrounding the deflection region and the detection element.
12 . The mass spectrometry system of claim 10 , wherein one of the particle shields of the pair of particle shields is configured to block the detection element from neutral species propagating through the mass analyzer.
13 . The mass spectrometry system of claim 10 , wherein successive portions of the iso-potential lines extending proximate to the ion entry opening encountered by the ion beam extend at decreasing angles relative to the first propagation axis such that, within the deflection region, the deflection path comprises a deflection radius with an end disposed at the vertex.
14 . The mass spectrometry system of claim 13 , wherein the deflector comprises a curved deflection surface, wherein at least a portion of the curved deflection surface comprises a deflector radius of curvature, as measured from the vertex, that is greater than or equal to half of the deflection radius.
15 . The mass spectrometry system of claim 10 , wherein the iso-potential lines extend parallel to the rear surfaces proximate to the pair of particle shields.
16 . The mass spectrometry system of claim 10 , wherein the deflector comprises a quarter of a sphere centered on the vertex, a quarter of an ellipsoid centered on the vertex, a quarter of a cylinder centered on the vertex, or wherein the deflector comprises a cross-sectional area that varies as a function of position along the vertex.
17 . A method detecting an ion comprising:
generating an ion beam propagating along a first propagation axis;
blocking neutral particles propagating with the ion beam by transmitting the ion beam through an ion entry opening of a first particle shield;
deflecting the ion beam off of the first propagation axis onto a deflection path by generating an electric field using a deflector disposed proximate a corner region disposed at an intersection between the first particle shield and a second particle shield, wherein the deflector comprises a pair of rear surfaces and a vertex where the pair of rear surfaces meet, the vertex being disposed proximate the corner region;
blocking additional neutral particles by transmitting the ion beam through an ion exit opening in the second particle shield; and
generating a detection signal from the ion beam using a detection element, wherein the electric field generated using the deflector comprises iso-potential lines that extend within 10° of perpendicular to the second particle shield in an area proximate to the ion exit opening.
18 . The method of claim 17 , further comprising focusing the ion beam at one or more of the ion entry opening and the ion exit opening using one or more ion focusing lenses.
19 . The method of claim 17 , wherein:
ions in the ion beam comprise a plurality of mass to charge ratios, and
applying a plurality of combinations of voltages to the deflector to direct the ions in the ion beam through the ion exit opening.
20 . The method of claim 17 , further comprising adjusting voltages applied to the deflector and to compensate for a kinetic energy distribution of the ions in the ion beam.