Shutdown raith SNF 2012-07-19 17:55:41: elevated pressures and a number of transient events

jwc at snf.stanford.edu jwc at snf.stanford.edu
Thu Jul 19 17:55:42 PDT 2012


Today and through the past week we have been observing elevated gun and system vacuum levels on the RAITH 150 system.  We observed a significant difference in system chamber pressure when the Column Chamber is opened and closed. This possibly may be a leak in the CCV assembly.
This morning and afternoon we oberved a number of transient events:
- The EHT power supply saw a voltage spike and shut the gun down.  11:48 AM 7-19-2012 
-The penning gage vacuum sensor has been noisy and irregular in its reading.
- The Z stage coder signals exhibited very unusual results in the mm range.  Drive to 5 mm set resulted in one arrival at 3.2 mm and later at 7.1 mm.
- Write field alignment results varied from any reality for no known reason. changing from 0.945 U and 0.956 V to 0.74 0.74 ( Possibly Indicating a bad W reading rfom reality.
- Users and myself experienced missing patterns that where verified written in the logs. last week I observed a pattern set that varied in its U coordinates albeit they were to be written in the same U , but different V coordinates. On one write last week some of my patterns were rotated from the U plane.
Users are requested to report missing or irregular pattern writes or other strange anomalies.
The only consistency is that when  the construction stops across the street some of these problems reduce in severity after 3:30 PM.
Strange but true we are evaluating logs on the system to seek out trends and root causes.
To protect the FE_GUN and the general state of the systems health I am shutting down the system to USERS overnight.  I have been in close contact with RAITH Field service in New York and locally and they will arrive in the early AM to continue and effect repairs.
Thank you,
James Conway




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