Please use caution working above 25 keV -- Collumn PM schedule for mid-February.

James Conway jwc at snf.stanford.edu
Fri Jan 23 16:53:31 PST 2004


Greetings:

All Users are requested to use caution when working above 25 keV.  We 
have been observing EHT power supply trips which may be brief arcing or 
corona discharge events at the FE-Gun tip.  There have been more than 
five of these EHT trips since we brought the system up at the beginning 
of the year -- all while working at 30 keV!

 > This seems to indicate that the tip is wearing out or there again is 
a problem in the EHT power supply. <

Today at 1500 hours we lost the RAITH image acquisition display card 
after a EHT trip event.  I had a spare board and have swapped it out.  
It may take up to a week to get a new card if they don't have a spare 
board handy in NY State.

SO PLEASE -- RAMP UP TO HIGHER KV IN SMALL STEPS. DO ALL YOUR 
ACCELERATION VOLTAGE REQUEST THROUGH THE RAITH COLUMN.NAV CONTROLS AND 
NOT FROM THE LEO SIDE.
I would recommend steps of 5, 10, 15, 20, 25 keV. 
 (This is very common practice in the 'old days' when FE-GUN tips were 
much more fragile and somewhat unreliable.)

Column PM:

Exact dates to be determined -- but we wish to minimize users impact if 
possible.

I have requested that LEO be available for a complete annual PM 
including aperture plate, final pole piece clean, and FE-GUN tip 
replacement and a full 40 hour bake out of the column to be scheduled 
for the Valentines Day weekend.
 The system would come down on February 13 at 9:00 AM. We hope to be 
back up and running on Tuesday February 17.  There will be some 
alignments and calibrations that need to be performed Tuesday morning.
 My goal is to have user access late the afternoon or evening of 2-17-2004.

Thank you for your support!

James Conway

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