Category Archives: General Optics and Vacuum

General information on repair, maintenance, and operation of both PHI (Physical Electronics) and other manufacturers’ systems and components

Ion Pump Rejuvenation Procedure

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After prolonged periods of sputtering with Argon gas, the ion pumps can become saturated, resulting in occasional “belches” of Argon during which the ion pumps overheat and release large amounts of gas. These belches usually result in a snowball effect that can dump the system. Rejuvenating the ion pumps once every few months (more often if you do a lot of sputtering) will help to prevent the belch problem from recurring.

To rejuvenate the ion pumps with O2:

1. Turn off all filaments, including the ionization tube (DIG).

2. Set the ion pump control panel meter to the 200mA current settings and set the

ion pump to the run (protected) mode.

3. Slowly bleed in O2 until there are 40mA of current shown on the ion pump panel meter. You will need to change ranges on the panel meter as the current is increased.

4. Adjust the leak valve as needed to maintain 40mA of current for 20 to 30 minutes.

5. Close the leak valve. It takes about one day for the vacuum to return to its previous level.

 

For more information on rebuilding ion pumps, search for Ion Pump in the RBD TechSpot blog search box.

For more information on ion pump theory, here is a link to an informative paper – https://cds.cern.ch/record/454179/files/p37.pdf

And, from Wikipedia:

An ion pump (also referred to as a sputter ion pump) is a type of vacuum pump capable of reaching pressures as low as 10−11 mbar under ideal conditions.An ion pump ionizes gas within the vessel it is attached to and employs a strong electrical potential, typically 3kV to 7kV, which allows the ions to accelerate into and be captured by a solid electrode and its residue.

The basic element of the common ion pump is a Penning trap. A swirling cloud of electrons produced by an electric discharge are temporarily stored in the anode region of a Penning trap. These electrons ionize incoming gas atoms and molecules. The resultant swirling ions are accelerated to strike a chemically active cathode (usually titanium). On impact the accelerated ions will either become buried within the cathode or sputter cathode material onto the walls of the pump. The freshly sputtered chemically active cathode material acts as a getter that then evacuates the gas by both chemisorption and physisorption resulting in a net pumping action. Inert and lighter gases, such as He and H2 tend not sputter and are absorbed by physisorption. Some fraction of the energetic gas ions (including gas that is not chemically active with the cathode material) can strike the cathode and acquire an electron from the surface neutralizing it as it rebounds. These rebounding energetic neutrals are buried in exposed pump surfaces.

Both the pumping rate and capacity of such capture methods are dependent on the specific gas species being collected and the cathode material absorbing it. Some species, such as carbon monoxide, will chemically bind to the surface of a cathode material. Others, such as hydrogen, will diffuse into the metallic structure. In the former example, the pump rate can drop as the cathode material becomes coated. And, in the latter, the rate remains fixed by the rate at which the hydrogen diffuses.

There are three main types of ion pumps, the conventional or standard diode pump, the noble diode pump and the triode pump.

Ion pumps are commonly used in ultra-high vacuum (UHV) systems, as they can attain ultimate pressures less than 10−11 mbar. In contrast to other common UHV pumps, such as turbomolecular pumps and diffusion pumps, ion pumps have no moving parts and use no oil. They are therefore clean, need little maintenance, and produce no vibrations. These advantages make ion pumps well-suited for use in scanning probe microscopy and other high-precision apparatus.

High Optical Quality Torr Scientific Vacuum Window used on ALBA

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Located in Barcelona, ALBA is a Synchrotron Light Source producing radiation for experiments in many fields of science, www.cells.es. The quality of the radiation delivered to users depends on the quality of the electron beam and it is therefore necessary to continuously monitor the beam status in a non-invasive way. At ALBA, the visible part of the synchrotron radiation itself is used to measure distribution of electrons in the machine. The used synchrotron radiation is guided far from the machine tunnel up to an “extraction mirror”. In order to maintain the vacuum in the tunnel, the radiation routed up to the mirror is in-vacuum too. A Torr Scientific viewport is used for extracting the light. The goal this year is to measure the transverse beam size by using the interference pattern produced by the synchrotron radiation passing through a double slits aperture. The performance of this kind of experiment requires the preservation of the quality of the light. Torr Scientific therefore provided a special viewport with a flatness better than lambda/10 and a curvature better than 1 arc sec. Accelerator Division Researcher Laura Torino
said ‘the special viewport we ordered fulfills all the requirements outstandingly; even better than what we were asking. Thank you for the great job you did’. This ALBA project is sponsored by oPAC.albaVPZ

How to test an ion gauge filament

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This post will explain how to test and replace the nude ion gauge filament assembly on a Physical Electronic (PHI) X-ray photoelectron, Auger electron or SIMS system. Look at the pictures at the bottom of the post before you read the procedures.

Background – On most PHI surface analysis systems the ion gauge filament is located either above the table tops in back of the vacuum chamber, or just under the tabletops.  The newer (as in less than 30 years old) systems have a cover that protects the user from the exposed electrical connections to the ion gauge pins. On the oldest PHI systems the ion gauge pins are exposed, but located under the table tops and difficult to access (and so relatively safe).

Here are links to some videos that explain how an  ion gauge works –

https://www.youtube.com/watch?v=IKKuWeEShM4

https://www.youtube.com/watch?v=6zv_Y0_vwsg

How to measure the resistance on the ion gauge:

  1. Turn off the DGCIII (or other brand of) ion gauge control.  This is not only the first step; it is the most important step! Ion gauge controls such as the DGCIII used on older PHI systems have about 200 volts of DC on the grid. If you do not turn off the DGCIII (or other) ion gauge control before removing the wires to the ion gauge you will likely receive a potentially lethal electrical shock. If you are not familiar with working safely with electricity then refer this procedure to qualified personnel.  Or, turn off the DGCIII and also and also unplug the 120 VAC power cord on the back of the DGCIII and then there is no danger of electrical shock.
  2. Loosen the set screws on the shield retaining collar. Do not loosen or remove the bolts that connect the ion gauge to the system! See the pictures at the bottom of this post for clarification.
  3. Loosen the strain relief screws and slide the shield out and away from the ion gauge, being careful to support the wires.
  4. Using an 048-4 spline wrench, loosen the ion gauge coupler set screws by turning the set screws closest to the flange CCW 1 to 2 turns and then gently pulling the coupler and wires off of the ion gauge pins. TIP: As you remove the couplers turn the set screws CW 1 turn so that they do not fall out of the couplers. RBD provides the 048-4 spline wrench and the setscrews.
  5. Use an ohmmeter and measure the resistance between the center filament pin (common) to the outside two filament pins. See the picture below. The pins resemble a smiley face and the filaments are the smile. The grid is the eyes (some ion gauges have 2 grid pins, some only one), and the collector is the center pin (nose). The filament resistances should be 1 ohm or less when measured from the center filament post to the outside two filament post. If a filament is burnt out (open) then the resistance will be infinite or some high value if there is a tungsten coating on the filament base.
  6. If one filament is burnt out but the other one is good, then you can switch filaments.  If you have 3 wires connected to the filaments then swap the outside two filament connectors. If you have just two filament wires, then move the outside filament wire to the other side.
  7. If both filaments are open, then the filaments need to be replaced. See the replacement procedure in the following section.

ion-gauge-wire-connection-types

ion-gauge-wire-connectionsHow to replace the ion gauge filaments:

  1. Vent the chamber.
  2. If not already done, remove the connectors from the ion gauge as per the previous procedure.
  3. Remove the bolts from the ion gauge flange.
  4. Remove the shield retaining collar.
  5. Carefully remove the ion gauge.
  6. Loosen the top set screws on the 3 filament base connectors. These are typically .050 hex screws.
  7. Remove the old filament assembly.
  8. Install the new filament assembly and tighten the set screws. Make sure that the filaments are parallel with the grid.
  9. Use a new copper gasket and place the ion gauge up to the flange. Make sure that the filaments are facing down. They will not line up perfectly parallel, so just choose the best position where the bolt holes line up. By facing the filaments down you will prevent any debris from falling onto the grid which may short out and damage the ion gauge control.
  10. Place the shield retaining ring up next to the ion gauge flange and rotate it so that the set screws in the shield retaining ring are accessible.
  11. Insert the bolts and tighten the flange.
  12. Reattach the ion gauge couplers. Make sure that the pins are bent slightly in towards the center collector wire so that none of the pins will short to the shield when it is installed.
  13. Carefully slide the shield over the wires and press the shield firmly into the shield retaining collar.
  14. Tighten the shield retaining set screws.
  15. Slightly tighten the strain relief screws.

That’s it!  Pump the system down and the ion gauge is ready to turn on once you get into the 10-4 Torr or better vacuum.

RBD Instruments provides replacement filament assemblies, complete ion gauge assemblies and the required spline and Allen wrenches. Contact us for more information.

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