Emission current measurement for superior instrument-to-instrument repeatability

Patent metadata

Field	Value
Publication number	US-11145502-B2
Application number	US-201916721517-A
Country	US
Kind code	B2
Filing date	Dec 19, 2019
Priority date	Dec 19, 2019
Publication date	Oct 12, 2021
Grant date	Oct 12, 2021

Abstract

An ion source assembly is described that includes an electron source configured to inject electrons into an ion volume to ionize an atom or molecule in the ion volume, wherein the electron source includes a filament. A lens electrode is positioned adjacent the electron source and includes an opening configured to pass electrons therethrough from the electron source into the ion volume. A supply voltage source is coupled to the filament and configured to supply a first voltage to the filament, wherein the first voltage is operable to ionize the molecules in the ion volume. Further, a bias voltage source is coupled to the supply voltage source and configured to supply a bias voltage to the lens electrode. Electrons striking the lens electrode are thereafter returned to the filament.

First claim

What is claimed is:

1. An ion source assembly, comprising:
an electron source configured to inject electrons into an ion volume to ionize an atom or molecule in the ion volume, wherein the electron source includes a filament;
a lens electrode positioned adjacent the electron source and including an opening, wherein the opening is configured to pass electrons therethrough from the electron source into the ion volume;
a supply voltage source coupled to the filament, wherein the supply voltage source is configured to supply a first voltage to the filament, wherein the first voltage is operable to ionize the molecules in the ion volume; and
a bias voltage source coupled to the supply voltage source and configured to supply a bias voltage to the lens electrode, wherein electrons striking the lens electrode are returned to the filament.

2. The ion source assembly of claim 1 , wherein the supply voltage source is configured to supply a second voltage to the filament, wherein the second voltage is inoperable to ionize the molecules in the ion volume.

3. The ion source assembly of claim 2 , wherein the supply voltage source is configured to alternate between supplying the first voltage and the second voltage.

4. The ion source assembly of claim 2 , wherein the first voltage is −70 volts and the second voltage is −20 volts.

5. The ion source assembly of claim 2 , wherein the lens electrode voltage is equal to 15 volts when the supply voltage source supplies the first voltage, wherein the lens electrode voltage is equal to 65 volts when the supply voltage source supplies the second voltage.

6. The ion source assembly of claim 1 , wherein the filament is electrically floated.

7. The ion source assembly of claim 1 , wherein the lens electrode is electrically floated.

8. The ion source assembly of claim 1 , wherein the ion volume is electrically grounded.

9. The ion source assembly of claim 1 , wherein the bias voltage source includes a direct-current (DC) bias power supply.

10. The ion source assembly of claim 1 , wherein the fixed voltage potential of the bias voltage source relative to the supply voltage source is 85 volts.

11. The ion source assembly of claim 1 , wherein the electron source is configured to inject electrons into the ion volume at a fixed or variable duty cycle.

12. An ion source assembly, comprising:
an electron source configured to emit electrons, wherein the electron source includes an electrically floated filament, wherein a first portion of the electrons enters an ion volume to ionize an atom or molecule in the ion volume;
a lens electrode positioned adjacent the electron source, wherein the lens electrode is electrically floated;
a supply voltage source coupled to the filament, wherein the supply voltage source is configured to supply a first voltage to the filament, wherein the first voltage is operable to ionize the molecules in the ion volume; and
a bias voltage source coupled to the supply voltage source and configured to supply a bias voltage to the lens electrode;
wherein the lens electrode is configured to collect a second portion of the electrons, wherein the second portion of the electrons flows back to the filament.

13. The ion source assembly of claim 12 , wherein the supply voltage source is configured to supply a second voltage to the filament, wherein the second voltage is inoperable to ionize the molecules in the ion volume.

14. The ion source assembly of claim 13 , wherein the first voltage is −70 volts and the second voltage is −20 volts.

15. The ion source assembly of claim 12 , wherein the bias voltage remains at a fixed voltage potential relative to the supply voltage source.

16. The ion source assembly of claim 15 , wherein the fixed voltage potential of the bias voltage source relative to the supply voltage source is 85 volts.

17. An ion source assembly, comprising:
a filament configured to emit electrons via thermionic emission;
a lens electrode surrounding the filament;
a first power supply coupled to the filament, wherein the first power supply is configured to supply a first voltage output at a first voltage slew rate to the filament, wherein the first voltage output is operable to ionize molecules;
a second power supply coupled to the lens electrode, wherein the second power supply is configured to supply a second voltage output at a second voltage slew rate to the lens electrode; and
a first capacitor coupling the first voltage output to the second voltage output.

18. The ion source assembly of claim 17 , further comprising a resistor coupled between the second voltage output and the lens electrode, wherein the first capacitor and the resistor are operable to align the first voltage slew rate with the second voltage slew rate.

19. The ion source assembly of claim 17 , further comprising a second capacitor configured to couple the second voltage output to an electrical ground, wherein the second capacitor is operable to reduce relative instrument-to-instrument variability in electron lens capacitance.

20. The ion source assembly of claim 17 , wherein the first power supply is configured to alternate between a high first voltage output and a low first voltage output, wherein the second power supply is configured to alternate between a high second voltage output and a low second voltage output, wherein the second voltage output remains at a fixed voltage potential relative to the first voltage output.

Assignees

• Thermo Finnigan Llc

Inventors

• Baldwin Lawrence G
• Smith Johnathan Wayne
• Mccauley Edward B

Classifications

• H01J49/022

  Circuit arrangements, e.g. for generating deviation currents or voltages (regulating electric or magnetic variables in general, e.g. current, magnetic field G05F); Components associated with high voltage supply (high voltage supply per se H02M) · CPC title

• H01J49/147 Primary

  with electrons, e.g. electron impact ionisation, electron attachment (H01J49/145 takes precedence) · CPC title

• H01J49/16

  using surface ionisation, e.g. field-, thermionic- or photo-emission · CPC title

• H01J49/067 Primary

  Ion lenses, apertures, skimmers · CPC title

• H01J49/26

  Mass spectrometers or separator tubes · CPC title