10-610 monochromator x-ray source anode replacement procedure

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This post will show how to replace the 10-610 monochromator X-ray source anode and filaments.  The 10-610 monochromator X-ray source is used in conjunction with the 10-410 or 10-420 monochromator.   When replacing the anode you should also replace both filaments and the deionizer cartridge (located in the 16-0XX heat exchanger).

Once the anode and filaments have been replaced the vacuum chamber needs to be baked out and the new filament and anode need to be out gassed and conditioned.  The monochromator may also need to be adjusted slightly to optimize the counts with the new anode and filaments.

Please read the entire procedure first, then watch the picture slideshow at the bottom of the post.

Anode replacement procedure

Vent the chamber.

Remove the water lines from the source.

Remove the safety cover from the source (3 screws).

Remove the high voltage cable

Remove the sixteen 5/16” bolts on the 6” flange and remove 10-610 mono source from the monochromator.

Next, remove the screw that connects the ground wire to the manifold.

Remove the Teflon block from the source base (2 spline cap head screws).

Remove the Teflon block from the source base.  Twist it as you slide it off the anode.

Loosen the nut on the high voltage connector (3/4” open end wrench) and remove the high voltage connector.

Remove the silicone rubber insulator and spring.  The spring makes electrical contact between the high voltage connector and the anode flange.

Remove the three spline cap head screws that hold the base to the flange and remove base from the flange. Note, this is optional as the base can stay on for bake out.

Remove the two screws that hold the filament cover on and remove the filament cover.

Remove the two screws that hold the filament cover support on and remove the filament cover support.  Note the position of the covers as you take them out as they need to go back the same way.

Remove the 6 cap head screws that hold the anode to the base and lift the old anode out of the source housing.

Separate the old anode from the anode flange.

Install a new O-ring on the new anode bottom and slide the anode flange into the new anode. There are 4 O-rings in the anode kit.  The anode flange forces the cooling water to the tip of the anode.

Use a new copper gasket and mount the new anode onto the anode flange.  Use care as you slide the anode in not to touch the sides of the anode housing (like the old game Operation).  The anode surface is coated with a thin layer of aluminum on a copper substrate.  Any contact with the top of the anode surface can cause little dents in the anode surface that can cause arc points.  Tighten the 6 cap head screws very lightly as the anode will need to be adjusted.

Using plastic tweezers or needle nose pliers, carefully rotate the anode until it is parallel to the filament housing. The idea is that the anode should be parallel to the anode housing and also centered so that there is a maximum and equal distance between the anode and the housing in order to prevent arcing.

Once the anode is parallel, tighten the six cap head screws on the base all the way down.

center the anode

center the anode

Next, if necessary loosen the 4 screws on the copper pedestal and move it to center the anode for maximum distance between the anode and the filament housing. If available,   you can use the anode alignment tool to help center the anode and then tighten the 4 screws on the base of the copper pedestal.

anode alignment tool

anode alignment tool

The anode surface should be the same level as the fence that is between the filaments and the anode.   If not loosen the spline head cap screw that secures the filament housing to the copper pedestal. You can use the anode alignment tool, a straight edge or just eye ball it.

Filament replacement procedure

The filaments are coated with Yttrium so that they can provide sufficient electrons for emission at a lower filament operating current. Be careful when handling the filaments so that you do not knock off any of the coating on the filaments.

Loosen the filament clamp screws on the large 7mm (diffused) area filament and remove the old filament. Note that the large 7mm filament is closest to the filament connector and wires.

Carefully insert the new filament into the filament clamps and lightly tighten them.  The filament should be centered with respect to the anode and the top of the filament should be even with the top of the filament cavity (level with the anode guard). It should also be parallel to the anode guard and centered in the filament cavity. If not, remove the filament and carefully bend the legs as needed. Once the filament height and centering is correct, firmly tighten the filament clamp screws.

Repeat this procedure for the small 2mm (focused) filament.

Install the filament cover base and cover.  Note that the little cut out goes over the 2mm filament.

Condition the anode and filaments procedure

Once the new anode and filaments have been installed onto the 10-610 monochromator X-ray source, the source needs to be baked out and then outgassed and conditioned.

First, bake out the system.

Next, outgas the filaments

Finally, condition the anode

Bake out the system

Follow the bake out procedure in the PHI manual or search for the RBD Techspot blog- Bake-out procedure to improve base vacuum.

The O-rings on the mono source, HV connector and silicone rubber insulator and Teflon block are all removed from the 10-610 mono source before bake out.  After bake out, use a little bit of vacuum grease on the O-rings to help provide a tight water seal when the Teflon block is replaced.

Replace the deionizer cartridge in the 16-0XX heat exchanger.  PHI recommends that the deionizer cartridge be replaced each time the anode is replaced to help make sure that the water does not react with the anode.

Outgas the filaments

Prior to outgassing the filaments the system should have been baked out and the mono source housing and water lines reassembled.  The deionizer cartridge should also have been replaced. The system should be cool and the base pressure in the low 10-9 to low 10-10 Torr range.

The filaments need to be initially outgassed slowly in order to prevent warping and also to set them.

Select the Outgas/ACT mode on the X-ray source controller.

Select the 2mm focused filament and ramp the current up to 5 amps in increments of .5 amps over a period of 2 to 5 minutes.   Wait for the outgassing to subside somewhat as indicated by the ion gauge.

Set the 2mm focused filament current to zero amps and then repeat the procedure with the 7mm diffused filament. Once up to 5 amps, let the 7mm diffused filament sit there for 4 to 8 hours or until the base vacuum returns to the low 10-9 Torr range.  Then set the filament current to zero and turn off the Outgas/ACT mode on the X-ray source controller.

Degas the Anode

Set the beam voltage to 500V and turn it on.

On the X-ray source controller, select the Outgas/ACT mode

Select the 2mm focused filament (Mg filament on a 32-095/6)

Slowly increase the amps to 3.5 and then monitor the anode current (emission current) meter.

VERY SLOWY increase the filament current until you get 1mA of emission current. Do not exceed 5 amps of filament current. Do not exceed 2mA of emission current.

Monitor the ion gauge vacuum reading and wait until the outgassing comes back down then slowly increase the beam voltage to 1 kV. If necessary reduce the filament current to keep the emission below 2mA.

In steps of 500V bring the high voltage up to 10kV while adjusting the filament current as needed to keep the emission current below 2mA. Do this over a period of 30 minutes to several hours, depending on how much the anode outgasses. For best results keep the vacuum in the chamber in the low 10-9 Torr range. The higher the pressure from outgassing, the more likely an arc will occur.

Once the anode has been outgassed to 10kV, turn the filament current to zero and set the high voltage to zero. Then switch to the other filament and repeat the procedure.

Condition the high voltage

Make sure that the Out/Act button is OFF and that the filament current is set to zero on both filaments.

SLOWLY bring the high voltage up to 10kV while monitoring the vacuum chamber ion gauge.

Step the high voltage up increments of 500V until you get to 16.5kV. When you see some signs of outgassing (the pressure in the vacuum chamber will come up) then back down the high voltage a little bit and wait until the vacuum recovers.

Once you are able to get to 16.5 kV with no arcing, let the anode sit there for at least 20 minutes.

The X-ray source is now ready for normal operation.   For best results, start at a low power and kV such as 100 watts and 10kV.   You can step up both the power and the kV over a period of a few hours based on how much outgassing you see when operating in this mode. Once you are up to full power of 300 watts and 15kv the X-ray source can be brought up to full power quickly.

Note that the maximum power that should be applied to the 2mm focused filament is 350 watts and the maximum power that should be applied to the 7mm diffused filament is 600 watts.  Personally I do not recommend more than 300 watts on either anode.  If you can get by with a lower wattage (such as 250) then both the filaments and anode will last longer.

It is also recommended that you inspect the 10-610 mono anode any time you vent your chamber for maintenance, or at least once a year. If you see indications of melting in the center of the anode you should replace the anode.  Otherwise it will eventually develop a water leak and cause potentially catastrophic damage to system components and substantial downtime.

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Reusing a Helicoflex gasket

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Can you re-use a Helicoflex gasket?  The answer is yes, sometimes.

A Helicoflex gasket uses the concept of plastically deforming to seal between two flat and polished surfaces instead of the much more common knife edge seal used with copper gaskets and CF flanges.

On Physical Electronics X-ray Photoelectron spectrometers Helicoflex gaskets are used on the monochromator, the SCA (spherical capacitive analyzer) and the LS specimen stage.

Here is a link to information on how a Helicoflex gasket works –  http://technetics.com/products/sealing-solutions/metal-seals/helicoflex-delta/

First of all, Helicoflex gaskets are designed to be used only once.   However,  since these gaskets are expensive it may be worth trying to reuse it as long as you have a new gasket on hand in case the trick I will show  you in this blog post does not work.  My success rate with this trick is about 50%.  RBD Instruments provides most of the Helicoflex gaskets used on PHI XPS systems.

For this example, I will attempt to make it possible to reuse a monochromator gasket as shown in the picture below.

monochromator_gasket

mono-chromator gasket

Note that once compressed, the center surface of the gasket is flattened out.

better_view_of_flat_area

Step one is to uncompress the gasket.   To do that, find a spot on the outside edge of the gasket where you can insert a small screw driver and gently spread open the two lips of the gasket enough to get a large flat head screwdriver inside.

insert_small_screwdriver

Then, carefully work the large flat head screw driver around the perimeter of the gasket until the entire gasket is un-compressed.  Try not to deform the edges of the slit.

insert_large_screwdriver

During this process the gasket will become deformed.  Use a round surface such as a Philips screwdriver to smooth out the bumps without re-compressing the gasket.

smooth_out

Next, using a very fine emery cloth (I used some 30uM 3M sand paper) smooth out the edges of the flat surface on the gasket.  You just want to break the edges, not make it round.

break_edge_on_flat

Clean the gasket with isopropanol or methanol to remove the small particles.

clean_with_IPA

Finally, use a small amount of Apiezon L or other HV or UHV vacuum grease to the surface of the gasket (on the flat area).   You want to use a very small amount and spread it out evenly.  The vacuum grease will help to fill in any small scratches.   Wipe off the inside and outside of the gasket.   You only want a small amount on the flat area.

small_amount_of_vacuum_grease

You are now ready to install the gasket.   Good luck!

The gasket that I used in this blog post did seal fine, so I got lucky.  🙂

 

 

Homemade Titanium Sublimation Pump

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In this post I show how we made a small homemade titanium sublimation pump for an 8” Kimball Physics spherical octagon UHV vacuum chamber.

Our little chamber has a 60 l/s ion pump, but even with baking (both IR and UVC), we were able to get only into the low 10-8 to high 10-9 Torr range.  However, using the little titanium sublimation pump, which we “Frankensteined” together using parts we had readily available, allowed us to get in the low 10-9 to high 10-10 Torr range, a factor of ten improvement.

A titanium sublimation pump works by heating a titanium filament wire to about 1300 degrees C. That is hot enough to create titanium gas molecules (sublimate) but not so hot that the filament wire melts.  The sublimated titanium deposits on the wall of the chamber (or preferably on a shield wall) and forms a thin film. This layer of titanium is very reactive and will bond with other molecules in the vacuum chamber such as CO and O2. Disassociated hydrogen and water vapor also diffuse into the titanium layer.

The reactivity of the titanium film is increased with lower temperatures, but most titanium sublimation pumps are operated at room temperature. Over time, the titanium film will become coated and need to be replenished. All commercial titanium sublimation pumps have 3 to 4 filaments so that when one filament burns out you can switch to another. Those filaments are also relatively thick in diameter at 12 gauge (.080”) and need about 50 amps of current to operate.

For our homemade titanium sublimation pump, we used 24 gauge (.020”) so that we could operate at a much lower current of 4 amps.  We also only have one filament.

Before I show how we made our homemade titanium sublimation pump, here are links to some videos on how TSPs work:

https://www.youtube.com/watch?v=j5Y7m2ZJfgg

https://www.youtube.com/watch?v=9vJedaxRsxI

The first thing that we needed was a 2-pin electrical feedthrough on a 2.75” CF flange.  For that we used a Getter pump flange from a PHI 04-303 ion gun as shown below.

filament_wire_connections

filament_wire_connections

We then needed to somehow support and electrically isolate the TSP filament wire. To do that we used a coupler and some little shoulder washers.

Ceramic_support

Ceramic_support

The top part of the getter pump assembly is conveniently designed to allow gas molecules to pass through but also block direct deposition of titanium into the vacuum chamber.

blocks_direct_deposition

Next we added a few turns into the titanium wire so that it would have a little bit of a spring to it. Then we connected the wire to the flange and support assembly. We have only one filament and so by effectively doubling the length of the wire we could also double the amount of titanium that we would be sublimating.

filament_wire

filament_wire

For a chamber wall we used a 2.75” nipple that has a tube ID of 1.6” and a length of 4”.  The larger the surface area the better, but for the size chamber that we have, we are limited to a small 2.75” nipple. We mounted this nipple on our chamber horizontally so that any flakes that form will not get into the chamber or ion pump.

2.75_inch_CF_nipple

2.75_inch_CF_nipple

For a power supply, we used a 30 volt 5 amp Lavolta.

30V_5amp_power_supply

30V_5amp_power_supply

After installing our homemade titanium sublimation pump into the chamber we pumped down and were ready to operate the TSP.

To operate our titanium sublimation pump, we slowly increased the power supply current while observing the color of the light coming off the TSP filament and also monitoring the chamber pressure.  The filament needs to be orange for the titanium to sublimate. Too hot and the lifetime of the filament will be reduced. Too low and the pumping effect is reduced. By experimenting we determined that about 3.8 amps DC was the correct amount of current.  Once that was determined, we could just periodically turn the TSP on for about 2 minutes at a time.  We did that 3 times over a 6-hour period and then let the chamber pump overnight. The next morning we were in the high 10-10 Torr range.  Success!

tsp_filament_in_operation

tsp_filament_in_operation

Conclusions:

  1. It is possible to make a small titanium sublimation pump using off-the-shelf components that will operate with less than 5 amps of DC current.
  2. Adding a titanium sublimation pump to a small chamber can help to get from HV to UHV.