Raith: please don't use 15-20.9KV or 23-30KV

[James Conway]

Ji-Won is correct that the dangerous range is the ~18 - 20 keV.  The 
threshold for the arcing events we observed before was in the 26.5 keV 
total acceleration voltage range. Keep in mind that the beam booster 
section of the column accelerated electrons from the 8 keV primary 
energy to the specified kEV through the 20 kEV range.  At 20001 - 20100 
Volts this section shuts off and ramps back to 0 and then without the 
beam booster section applied accelerates electrons to the specified 
higher acceleration voltage.  So 20 kEV results in 28 kEV potential 
between the gun tip and the anode plate.

I have requested LEO to return to assist in evaluating this problem, but 
with no response thus far.  I escalate this with LEO in Germany in the 
morning Friday their time.

 Mike Santomango with LEO has been MIA since I returned from Germany two 
weeks ago, and I am continuing attempts to reach him,  or someone with 
suitable knowledge here in the USA.

Thank you for your support!

James Conway

Ji-Won Son wrote:

>Hi Mark,
>
>Thank you for the message. But one thing which is not clear to me is that
>why the range between 20.1-20.9 is included in the dangerous range. As far
>as I know, the most dangerous range is 15 to 20 kV, and 23 kV and higher
>(where the actual acc. voltage is higher than 23 kV). Does anyone experience
>problem in the range of 20.1 to 20.9kV? 
>
>I would appreciate your help. Thank you.
> 
>=======================
>Sincerely,
>Ji-Won Son
> 
>Office: (650) 723-4940
>Fax: (650) 725-3459
>=======================
> 
>
>-----Original Message-----
>From: Mark Topinka [mailto:mtopinka at stanford.edu] 
>Sent: Wednesday, April 21, 2004 8:01 PM
>To: raith at snf.stanford.edu
>Subject: Raith: please don't use 15-20.9KV or 23-30KV
>
>(in other words, 0-15KV is ok and 21-23KV are probably ok, but DO NOT set 
>it to 15-20.9KV or 23-30KV : these ranges cause intermittent EHT trips, 
>which can occasionally turn into the more serious and dreading "arc", which 
>can ultimately seriously damage the instrument)   Sylvia had problems with 
>repeated EHT trips (even after a LONG pumpdown) today and we do not want a 
>repeat of what happened earlier this year (right!?) until we sort out what 
>exactly is going on.  -Mark
>  
>