FEG Source Replacement

The FE source has been unstable, emission current is much higher that normal (>~ 300 uA). This particular source has never been stable since its installation in March-April. Beam currents ~ 50% of optimum value. Extractor voltage was 5300 V for normal current, makes it difficult to get high currents without gun vacuum problems.

We had accepted this filament late April 2012 despite marginal performance. This was already the third filament installed, multiple service visits trying to get specs, etc. We accepted system in order to get back to work. In retrospect probably a mistake, filament evolution/changes made high res work a challenge.

Virginia has negotiated a replacement with Zeiss, somewhat delayed by the recent changes to the service organization when electron and optical microscopy groups were combined. At first Zeiss claimed no record of our service contract.

• Initial request to replace source due to poor performance early November 2012
• Nov 8 zeiss reply not covered by service contract
• Virginia appeals to Okan Sener, Zeiss, he approves replacement about Nov 10
• Nov 12 Zeiss comes back that we have no active service contract, their error, it has been active continuously warranty or service contract since 2006
• Nov 15 Zeiss agrees we do in fact have service contract
• Phil shows up Tuesday 11/20 do replace source but without warning us, scope is busy, then thanksgiving
• Phil reschedules for Monday 11/26
• Source replaced 11/27-28. Some stability problems. Phil says give it a try, he will return on Friday 11/30
• Reschedules for Tuesday 12/4
• Frank finds "double image" conditions for 20/30 um apertures on 12/3
• On 12/4 Phil sends recommendation to replace apertures, etc, before return visit
• Virginia requests quote 12/4
• Robert comes Thursday/Friday 12/5-6 for Ultra turbo problem, does not get to supra
• Monday 12/10 vents SEM, uses Ultra to image Supra apertures and source. Finds no visible problems, reassembles and bakes microscope
• Tuesday 12/11 works on alignment. Gun vacuum back, image unstable, extractor current low and dropping
• Glenn comes Wed 12/13 and Thurs 12/14. 
• Works on aligning re-installed source. 
• Thursday afternoon image instability reduced but not eliminated.
• Concludes source will not meet current specs or image quality, will install new source. 

• Order full set of replacements parts (apertures, beam tube etc) for replacement in Jan. Delays getting multi-hole aperture
• parts arrive Wed 15 Jan
• Robert here Thurs Fri. On Thurs check pumping apertures, beam cap on bottom of column. No help. Change source, parts, bake.
• Friday Robert does alignment, reports a couple of image glitches but stable for last hours, also beam currents "a bit low".
• Filament 2.40 A, 5.8 kV extractor, 4.3e-10 gun vac on Monday, 110.8 uA beam off