END CAP VOLTAGE CONTROL OF ION TRAPS

• US 20090146054A1
• Filed: 12/08/2008
• Published: 06/11/2009
• Est. Priority Date: 12/10/2007
• Status: Active Grant

• Current Assignee: Astrotech Technologies, Inc. (Astrotech Corporation)
• Original Assignee: Spacehab, Inc.
• Inventors: Rafferty, David
• Granted Patent: US 8,334,506 B2
• Time in Patent Office: Days
• US Class Current: 250/281
• CPC Class Codes: H01J 49/26 Mass spectrometers or separator tubes
• CPC Class Codes: H01J 49/424 Three-dimensional ion traps, i.e. comprising end-cap and ring electrodes

Abstract

An ion trap for a mass spectrometer has a conductive central electrode with an aperture extending from a first open end to a second open end. A conductive first electrode end cap is disposed proximate to the first open end thereby forming a first intrinsic capacitance between the first end cap and the central electrode. A conductive second electrode end cap is disposed proximate to the second open end thereby forming a second intrinsic capacitance between the second end cap and the central electrode. A first circuit couples the second end cap to a reference potential. A signal source generating an AC trap signal is coupled to the central electrode. An excitation signal is impressed on the second end cap in response to a voltage division of the trap signal by the first intrinsic capacitance and the first circuit.

Claims

1. An ion trap comprising:

a conductive ring-shaped central electrode having a first aperture extending from a first open end to a second open end;

a signal source generating a trap signal having at least an alternating current (AC) component between a first and second terminal, wherein the first terminal is coupled to the central electrode and the second terminal is coupled to a reference voltage potential;

a conductive first electrode end cap disposed adjacent to the first open end of the central electrode and coupled to the reference voltage potential, wherein a first intrinsic capacitance is formed between a surface of the first electrode end cap and a surface of the first open end of the central electrode; and

a conductive second electrode end cap disposed adjacent to the second open end of the central electrode and coupled to the reference voltage potential with a first electrical circuit, wherein a second intrinsic capacitance is formed between a surface of the second electrode end cap and a surface of the second open end of the central electrode, wherein a fractional part of the trap signal is impressed on the second electrode end cap in response to a voltage division of the trap signal by the second intrinsic capacitance and an impedance of the first electrical circuit.

2. The ion trap of claim 1, wherein the first electrical circuit comprises a capacitor in parallel with a resistor.

3. The ion trap of claim 2, wherein an impedance of the resistor is greater than one fourth of an impedance of the capacitor at a frequency of the trap signal.

4. The ion trap of claim 1, wherein the reference voltage potential is ground or zero volts.

5. The ion trap of claim 1, wherein the reference voltage potential is an adjustable DC voltage.

6. The ion trap of claim 1, wherein the capacitor is a variable capacitor adjustable to optimize an operating characteristic of the ion trap.

7. An ion trap, comprising:

a central electrode having an aperture;

a first end cap electrode having an aperture;

a second end cap electrode having an aperture;

a first electronic signal source applied to the central electrode;

a circuit of passive elements;

an electrical connection between said first end cap electrode and said circuit of passive elements; and

an electrical connection between said circuit of passive elements and a voltage potential, wherein said first end cap electrode connected to said voltage potential via said circuit of passive elements bears a voltage due to capacitive coupling between said first electronic signal source and said circuit of passive elements.

8. An ion trap claim 7, further comprising a switching circuit that electrically connects and disconnects said first end cap electrode to said circuit of passive elements.