<div dir="ltr"><div class="gmail_default" style="font-family:georgia,serif;font-size:small">I think what you see in the video, when the Emissions current spikes to ~130mA, is an electrical arc - the HV suddenly arcs to ground or somewhere. Looks for burn marks around insulators etc. to see if you can locate the arcing region.</div><div class="gmail_default" style="font-family:georgia,serif;font-size:small"><div class="gmail_default">I agree to check the ceramic insulators- miniscule fractures or metal coating could cause such arcs.</div><div class="gmail_default"><br></div><div class="gmail_default">On our Ion-beam dep, we've found that hard to see cracks in the many ceramic insulators around wiring will enable similar arcing, causing Currents to spike like in your video – the power supply then faults temporarily (for a split second), shutting it off and then attempts to recover back to the setpoint.</div></div><div><div dir="ltr" class="gmail_signature" data-smartmail="gmail_signature"><div dir="ltr"><div><div dir="ltr"><div style="font-family:"times new roman",serif;font-size:small"><div><font size="4">-- Demis</font></div><div><font size="4"><br></font></div><div><font size="4">----------------------------------------</font></div><div style="font-family:Arial,Helvetica,sans-serif"><i style="font-family:"times new roman",serif"><font size="4"> Process Scientist Manager</font></i><br></div><div><font size="4"> <font color="#1155cc"><a href="https://www.nanotech.ucsb.edu/" target="_blank"><i>UCSB Nanofabrication Facility</i></a></font></font></div><div><font size="4"> <a href="https://wiki.nanotech.ucsb.edu/wiki/Demis_D._John" target="_blank">Demis' Contact Info</a></font></div><div style="font-family:Arial,Helvetica,sans-serif"><div style="font-family:"times new roman",serif"><font size="4">----------------------------------------</font></div><div><font size="4"><font face="times new roman, serif"><i>Reminder</i>: The NanoFab has a <a href="https://wiki.nanotech.ucsb.edu/wiki/Frequently_Asked_Questions#Publications_acknowledging_the_Nanofab" target="_blank">publications policy</a></font></font></div></div></div></div></div></div></div></div><br></div><br><div class="gmail_quote"><div dir="ltr" class="gmail_attr">On Fri, Jul 9, 2021 at 8:41 AM Khanna, Rohit <<a href="mailto:r.khanna@ucl.ac.uk">r.khanna@ucl.ac.uk</a>> wrote:<br></div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left-width:1px;border-left-style:solid;border-left-color:rgb(204,204,204);padding-left:1ex">
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<div style="font-family:Calibri,Arial,Helvetica,sans-serif;font-size:12pt;color:rgb(0,0,0)">
Hi,</div>
<div style="font-family:Calibri,Arial,Helvetica,sans-serif;font-size:12pt;color:rgb(0,0,0)">
Based on the video that was shared, I suspect there is an issue with the filament current. </div>
<div style="font-family:Calibri,Arial,Helvetica,sans-serif;font-size:12pt;color:rgb(0,0,0)">
To begin with I am not sure how thick the filament is and 26 Amp seems on the high side.</div>
<div style="font-family:Calibri,Arial,Helvetica,sans-serif;font-size:12pt;color:rgb(0,0,0)">
Check the manual if the filament is rated to work at such high currents. Secondly check the </div>
<div style="font-family:Calibri,Arial,Helvetica,sans-serif;font-size:12pt;color:rgb(0,0,0)">
the power supply that runs the filament as in the video there was a dip in the filament current</div>
<div style="font-family:Calibri,Arial,Helvetica,sans-serif;font-size:12pt;color:rgb(0,0,0)">
before the emission current dipped. The emission current is highly dependent on the filament temperature</div>
<div style="font-family:Calibri,Arial,Helvetica,sans-serif;font-size:12pt;color:rgb(0,0,0)">
which depends on the filament current. For 26-30 amp filament current the cable should be fairly thick and </div>
<div style="font-family:Calibri,Arial,Helvetica,sans-serif;font-size:12pt;color:rgb(0,0,0)">
any issue with the vacuum feed thru or connector (corroded or oxidized will lead to localized heating or melting).</div>
<div style="font-family:Calibri,Arial,Helvetica,sans-serif;font-size:12pt;color:rgb(0,0,0)">
Check the cable connector and filament power supply before sensing the unit back.</div>
<div style="font-family:Calibri,Arial,Helvetica,sans-serif;font-size:12pt;color:rgb(0,0,0)">
<br>
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<span style="color:rgb(33,33,33);font-family:"Freestyle Script";font-size:18pt">Rohit Khanna</span></div>
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<div id="gmail-m_2189032515894789638divRplyFwdMsg" dir="ltr"><font face="Calibri, sans-serif" style="font-size:11pt" color="#000000"><b>From:</b> labnetwork <<a href="mailto:labnetwork-bounces@mtl.mit.edu" target="_blank">labnetwork-bounces@mtl.mit.edu</a>> on behalf of Stephen Howe <<a href="mailto:info@fabsurplus.com" target="_blank">info@fabsurplus.com</a>><br>
<b>Sent:</b> 09 July 2021 09:13<br>
<b>To:</b> Nathanael Sieb <<a href="mailto:sieb@4dlabs.ca" target="_blank">sieb@4dlabs.ca</a>>; <a href="mailto:labnetwork@mtl.mit.edu" target="_blank">labnetwork@mtl.mit.edu</a> <<a href="mailto:labnetwork@mtl.mit.edu" target="_blank">labnetwork@mtl.mit.edu</a>><br>
<b>Subject:</b> Re: [labnetwork] troubleshooting an e-beam source</font>
<div> </div>
</div>
<div style="text-align:left;direction:ltr">
<div>In my opinion, you need to study the problem more methodically using the data you have to find the cause of the problem.</div>
<div>For starters I would plot graphs of how all the parameters you are measuring change during the incident, which should allow you to see what is causing the problem.</div>
<div>I would guess it looks like a high voltage breakdown.</div>
<div>That can be often due to bad insulation or a vacuum problem .</div>
<div>A part of a high voltage circuit that often fails is the driver part for the signals which end up sitting at high voltage.</div>
<div>As the control signals go from the part of the circuits at low voltage to the part of the circuits at high voltage, they have to pass through some kind of transformer, which can suffer from problems of large back emfs , which can blow the drivers.</div>
<div><br>
</div>
<div>Yours sincerely,</div>
<div><br>
</div>
<div>SDI Fabsurplus Group</div>
<div>Stephen Howe</div>
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<div>On Thu, 2021-07-08 at 10:07 -0700, Nathanael Sieb wrote:</div>
<blockquote type="cite" style="margin:0px 0px 0px 0.8ex;border-left-width:2px;border-left-style:solid;border-left-color:rgb(114,159,207);padding-left:1ex">
<p>Hi all,</p>
<p>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.<br>
</p>
<p>We took a video of the issue and it happens at around the 1min mark <a href="https://eur01.safelinks.protection.outlook.com/?url=https%3A%2F%2Fwww.dropbox.com%2Fs%2F7n42e38qviju7ga%2FBoth_emission_and_filament_spiking_and_turning_off.mov%3Fdl%3D0&data=04%7C01%7C%7Cdd69e26f9c4142a0830808d942cdfb99%7C1faf88fea9984c5b93c9210a11d9a5c2%7C0%7C0%7C637614276381113135%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000&sdata=w6o5i64gVrOTPzuYA%2FOFN3nmy0wb2Ufv1Zn9aULhVLY%3D&reserved=0" target="_blank">
here</a>. 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.</p>
<p>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?</p>
<p>Thanks,<br>
Nathanael<br>
</p>
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<pre>_______________________________________________</pre>
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