Langmuir Probe Test

29 07 2011

All photos.

Today I did a successful test of the Langmuir probe:

 

Here is a voltage reading of the floating potential:





New Materials for Electron Beam Melting

26 07 2011

Previously I looked into Arcam’s 3D Metal process. At the time, Arcam’s Ti6Al4V Titanium Alloy seemed the best option.

Today I checked back to Arcam’s materials page and it’s been expanded to include:

I’m happy to see stainless steel and amorphous metals (although the stainless 17-4 is magnetic).

Soon I will be ordering calibration parts using a variety of 3D printing technologies and materials.

UPDATE: Also check out this amazing polishing technology: Electron Beam Machining. This might be perfect for polishing 3D printed  metal pieces.




Galling!

21 07 2011

The nuts and bolts for the large flange are galling:

This set is shot.

These sets are pretty expensive, so I asked MDC for a free replacement… which they gave me!

Galling is pretty common with stainless on stainless. One solution is to use anti-sieze:

But this introduces goopy hydrocarbons to my clean chamber.

MDC’s recommended solution is silver plated stainless steel bolts. At $77 for a large conflat it’s very expensive… but the way to go.

 

 





If At First You Fail: Cheat

21 07 2011

All photos.

The delicate assembly I made yesterday fell apart when I tried to assemble it today.

So I’m taking the easy way out… I will use one strand from this stranded silver-plated teflon-insulated wire:

Much sturdier!

Now I have a fully assembled Langmuir probe:





Building the Langmuir Probe

20 07 2011

All photos.

Today I began fabricating the Langmuir probe.

I am using a tungsten light bulb filament as the probe tip:

The rest is just ceramic tubing to hold it in place.  The filament is so thin and so fragile.

I use insulating varnish to hold it all together. I have to let this cure over night:

This will attach to the feedthrough:

The Langmuir probe will show the floating potential of the plasma… The dependent variable in the Sydney Experiment.





Electron Gun: Spark the Plasma

19 07 2011

All Photos.

Just completed a test of the new electron gun with air plasma. Looks good:

 

To get here I had to reconnect all the ground leads:

And wire up the high voltage:





Mass Flow Controller Upgrade

18 07 2011

All photos.

Today I upgraded the Mass Flow Controller (MFC):

Previously I used a 9V battery + a potentiometer as a quick hack to control the MFC.

For the sake of fewer parts I wanted to remove the battery from the circuit. The power supply for the MFC provides +15V, which is way over the 0 to +5V I need to control the MFC.

To prevent over voltage I used a TVS diode which shorts to ground above +6V.

It seems to all work! Don’t have to worry about a dead battery now.

Schematic:

 

The hard part is the craftsmanship needed so it won’t short out. Work in progress:

 








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