[labnetwork] troubleshooting an e-beam source

[Paolini, Steven]

Nathanael,
  Does it stabilize at low power? Does it get worse at high power?
  I would be highly suspicious of your HV feedthroughs. You state that you removed the "assembly" in which I presume is the E-beam gun and hearth. By doing this, you would have to had removed the HV leads off the feedthroughs. It is very easy and not noticeable to crack the ceramic insulators when reinstalling the leads. There is also a good chance after disturbing them that you unintentionally made a path to ground with any leftover metal debris.
Shut down the HV power supply and lock it out. Ground the atmosphere side leads with a "chicken stick" to ensure there is no power present and remove the atmosphere side leads. Next, remove the vacuum side HV leads and check the center post of each feedthrough to ground with an Ohmmeter. The reading must be infinity. A better way to do this is with a Megger since you can test insulation properties with the power the Megger has.
I hope this helps,
    Equipment Dood


________________________________
From: labnetwork <labnetwork-bounces at mtl.mit.edu> on behalf of Nathanael Sieb <sieb at 4dlabs.ca>
Sent: Thursday, July 8, 2021 2:07 PM
To: labnetwork at mtl.mit.edu <labnetwork at mtl.mit.edu>
Subject: [labnetwork] troubleshooting an e-beam source


Hi all,

We are trying to trouble-shoot a PVD e-beam source and can't seem to figure out the problem.  Early in the year we sent the assembly out for repair and refurbishment. (we burned a hole in the internal bellows tubing, long story)  When we got it back we connected it back to the system and started it up.  However, we haven't been able to get a stable emission current.  The HV stays on but the filament current, and hence emission current, occasionally cuts out.  It comes back a second later, over-shoots the target current, and then restabilizes.  It happens at low emission currents and some higher ones.  The timing is random.  Sometimes it happens frequently, sometimes you can run 15 min without a problem.  There are no errors from the power supply.

We took a video of the issue and it happens at around the 1min mark here<https://urldefense.proofpoint.com/v2/url?u=https-3A__www.dropbox.com_s_7n42e38qviju7ga_Both-5Femission-5Fand-5Ffilament-5Fspiking-5Fand-5Fturning-5Foff.mov-3Fdl-3D0&d=DwMDaQ&c=WO-RGvefibhHBZq3fL85hQ&r=-H4Z_jeDfTYjnKPXor15vLwzBllmg8gFrb9m_k9OGks&m=3B8QHctyJzDB-8PBQ1cp4rp0rhyiDZONrHx8mjetE8k&s=y_RvJEM7tqoERdj0tmtOfeMjpeliA3XJFcH3yhAZ2P4&e=>.  The advice from vendors was to look for a loose connection.  We have checked all the external connections and tried to look at the internal ones too.  Last week we removed the filament and reinstalled it.  We didn't see any problems and we still have the same issue.

We're running out of ideas other than sending it back to the vendor to examine the entire assembly again.  Has anyone else encountered this type of problem?  Any suggestions?

Thanks,
Nathanael

Nathanael Sieb
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