Differential pumping stage with line of sight pumping mechanism

• US 5,646,488 A
• Filed: 10/11/1995
• Issued: 07/08/1997
• Est. Priority Date: 10/11/1995
• Status: Expired due to Term

• Current Assignee: William K. Warburton
• Original Assignee: William K. Warburton
• Inventors: Warburton, William K.
• Primary Examiner(s): Pascal, Robert
• Assistant Examiner(s): Philogene, Haissa
• Application Number:
  US08/540,806
• Time in Patent Office: 636 Days
• Field of Search: 315/111.81, 315/111.91, 315/111.21, 315/111.41, 315/111.01, 315/108, 315/5.42, 315/5.35, 315/5.24, 315/5.26, 315/5
• US Class Current: 315/111.81
• CPC Class Codes: G21K 1/10 Scattering devices; Absorbing devices; Ionising radiation filters
• CPC Class Codes: H01J 7/14 Means for obtaining or maintaining the desired pressure within the vessel
• CPC Class Codes: H05H 7/00 Details of devices of the types covered by groups H05H9/00, H05H11/00, H05H13/00

Abstract

An apparatus allows photons in the infrared, visible, ultraviolet, soft x-ray and hard x-ray energy ranges to pass freely along a line of sight path between two vacuum regions at different pressures, yet maintains the pressure difference between the two regions and, in particular, removes vapor species attempting to pass between the two regions along the line of sight path. The apparatus works by causing the line of sight path to pass through a volume provided with a pumping mechanism which is transparent to the photons. Within this volume the vapor species are ionized and deviated from the line of sight by both magnetic and electric fields. The ionization mechanism is provided by an electron plasma created by the Penning discharge mechanism in an equipotential volume between two sets of electrodes. Vapor species attempting to pass through the electron plasma are ionized by collisions with the electrons in the plasma and removed from the line of sight path by the magnetic and electric fields used to maintain the Penning discharge.

Claims

1. A method which provides a line of sight path for photons to pass freely between two vacuum regions while pumping vapor species which attempt to travel between the two regions along the line of sight path, the method comprising the steps of:

ionizing the vapor species attempting to move along the line of sight path; and

removing the vapor species, so ionized, from the line of sight path by the use of electric and/or magnetic fields.

2. The method of claim 1 wherein:

the vacuum regions are at different pressures; and

said ionizing step is performed in an intermediate region between the vacuum regions and is performed on vapor species traveling through the intermediate region, including vapor species traveling along the line of sight path.

3. The method of claim 1 wherein said ionizing step includes:

providing an anode structure having an open portion surrounding the line of sight path in an intermediate region between the two vacuum regions;

providing a cathode structure having opposed portions separated by said anode structure; and

applying an electrical voltage between the anode and cathode structures so as to generate an electron plasma in the intermediate region.

4. The method of claim 1 wherein said ionizing step further includes:

generating a magnetic field generally perpendicular to the line of sight path.

5. A method for maintaining an unimpeded line of sight path between a first vacuum region at a first pressure and a second vacuum region at a second pressure that is significantly lower than the first pressure, the method comprising the steps of:

generating an electron plasma in an intermediate region disposed in the line of sight path so as to ionize vapor particles travelling through the intermediate region, including particles travelling along the line of sight path;

deflecting the ionized particles out of the line of sight path; and

pumping the second vacuum region.

6. The method of claim 5 wherein said deflecting step includes providing a magnetic field having a component perpendicular to the line of sight path.

7. The method of claim 5 wherein said generating step includes the step of maintaining a Penning discharge in the intermediate region.

8. The method of claim 5 where the electron plasma is extended from a region wherein it is created into the line of sight path by causing the intermediate region surrounding the line of sight path to be at the same electrostatic potential as the region wherein the plasma is created.

9. Apparatus for maintaining an unimpeded line of sight path between a first vacuum region at a first pressure and a second vacuum region at a second pressure that is significantly lower than the first pressure, the apparatus comprising:

an anode structure having an open portion surrounding the line of sight path in an intermediate region between the first and second vacuum regions;

a cathode structure having opposed portions separated by said anode structure;

an electrical voltage generator coupled between the anode and cathode structures, the voltage generator having a sufficiently high voltage output to generate an electron plasma in the intermediate region; and

a magnet having opposed pole elements disposed outside said cathode structure so as to generate a magnetic field generally perpendicular to the line of sight path.

10. The apparatus of claim 9 wherein:

the anode structure comprises a plurality of parallel metal tubes extending perpendicular to the line of sight path with at least some tubes being shorter than other tubes; and

the open portion of the anode structure is defined by spaces between spaced pairs of the shorter tubes.

11. The apparatus of claim 9 wherein:

the cathode structure comprises first and second pluralities of metal strips extending in respective first and second planes on opposite sides of the anode structure.

12. A method which provides a line of sight path for photons to pass freely between two vacuum regions while pumping vapor species which attempt to travel between the two regions along the line of sight path, the method comprising the steps of:

using a Penning discharge to create an electron plasma within a volume through which the line of sight path passes so as to ionize vapor species passing through the volume, including the vapor species attempting to move along the line of sight path; and

removing the vapor species, so ionized, from the line of sight path by the use of electric and/or magnetic fields.

13. The method of claim 12 wherein:

the Penning discharge is maintained with electric and magnetic fields; and

the electric and/or magnetic fields used to remove the vapor species, so ionized, are the same electric and magnetic fields used to maintain the Penning discharge.